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Oct. 8, 1946.
2,409,033
L. GARCEAU
ELECTROENCEPHALOGRAPH DEVICE
Filled Nov. 4, 1941
7 Sheets-Sheet 1
\NVENTOR
Luvs-:1"; .E'RRGEHL!
BY
l/WM +
ATTORNEYS .
Oct. 8, ‘1946. '
L. GARCEAU
‘2,409,033
ELECTROENCEPHALOGRAPH DEVICE
Filed NOV. ‘4, 1941
8
7 Sheets-Sheet 2
42
60
PR 70
b;
INVENTOR.
LDVETT EHRCEFILJ
A‘ILORNEYS .
Oct’ 8, 194,6.
‘
L. GARCEAU
ELECTROENCEPHALOGRAPH DEVICE
File'd Nov. 4, 1941
2,409,033
_
'7 Sheets-Sheet 4
FIE--5
64
76
70
.75
INVENTOR,
LUVETT E'FIR'EEHLJ
ATTORN EYS'.
Oct. 8, 1946.
2,409,033
L. GARCEAU
ELECTROENCEPHALOGRAPH DEVICE
Filed Nov. 4, 1941
7 Sheets-Sheet 5
ENVENTOR '
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Oct. 8, 1946.
|_. GARC'EAU
2,409,033 '
ELECTROENCEPHALOGRAPH DEVICE
Fil'ed Nov. 4, 1941'
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ATTORNEYS‘.
Oct“ 8, 19466
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1.. GARCEAU
2,409,033
ELECTROENCEPHALOGRAPH DEVICE
Filed Nov. 4,‘ 1941
7 Sheets-Sheet '7
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Lever?’ E’HRC'EHLJ
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ATTORNEYS.
2,409,033
Patented Oct. 8, 1946
UNITED STATES PATENT OFFICE
2,409,033
ELEC'I‘BOENCEPHALOGRAPH DEVICE
Lovett Garceau, .Holliston, Mass.
Application November 4, 1941, Serial No. 417,865
12 Claims. (Cl. 128—'2.1)
1
2
Referringnow to the drawings:
This invention relates to improvements in elec
troencephalcgraph devices and has for an object
Figure 1 is a perspective view of my new and
the provision of a simple and reliable means for
recording electroencephalograms and other elec
improved electroencephalograph device with the
trical electrophysiological potentials.
Figure 2 is a front elevation of the device
shown in Figure .1, said device having been .re
moved from the cabinet;
cover opened and partly broken away;
Another object of the invention ‘is the provi
sion of an electroencephalograph device provided
with effective shielding, the provision of attach
Figure 3 is a rear view of the device shown in
ments for connection to said device and to a
Figure 2;
shielding devices making it unnecessary for the
patient to be placed in a “Faraday cage.”
Another object of the invention is the provi
sion in apparatus of the character described of
a record feed device for advancing the record at
a uniform and de?nite rate, and the provision
the bottom thereof;
Figure 7 isan elevation of the recording tape
mechanism removed from the device and show
patient, said connections being provided with 10
Figure 6 is a view of the device as seen from
ing the portion of the device engaged thereby in
elevation;
of a stylus traversing a station over which the
record passes for recording wave forms or other
graphs on the record.
A further object of the invention is the pro
vision in a thermionic device of an ampli?er in
cluding at least two tubes in its input stage, the
provision of a multiplicity of electrodes and
switching means associated with said electrodes
and the input grids of said tubes, said switching
devices being arranged so that, for example, two
of the electrodes may be selectively associated
with said input grids and the remaining elec
trodes being all connected together and ground
ed,'0r separately grounded through individual re
sistive‘paths.
Yet another object of the invention is the pro
vision in a thermionic device of a plurality of
Figures 4 and 5 are, respectively, right and left
end views .of the device shownin Figures 2 and 3;
Figure 8 is an end elevation of the recording
tape mechanism as seen along the line 8—8 of
v20
Figure .3;
Figure .9 is a plan view of the portion of the
device for containing the recording tape mech
anism and showing details of the tape drive and
therecording mechanism;
Figure 10 is a diagram of the internal circuits
of the device;
Figure 11 is a plan view of one form of elec
trode support, the same being adapted to be
applied to .the headof the patient for supporting
the electrodes in a very large number of combi
nations of positions;
Figure 12 is a, transverse sectional elevation of
the electrode holder shown in Figure 11;
Figure 13 is a view showing a shielded cable
shielded conductors connected thereto, a plu
rality of electrodes for contacting human ?esh 35 carrying a plurality ofccnductors for attach
ment to the electrodes shown in the holder in
or tissue, a support generally conforming to the
Figures 11 and 12;
~
shape of a portion of the human head and adapt
Figure .14 is an enlarged view showing details
ed to support electrodes in contact with human
of one .of the electrodes; and
flesh or-tissue in a desired selective arrangement,
with respect to each other, and connections be- 40 Figure 15 is a diagram showing theswitching
arrangementfor a plurality of electroencephalo
tween said electrodes and said shielded conduc
graph channels.
'
tors.
By employing an ampli?er which includes at
A further object of the invention is the provi
least two input tubes (or two control grids in a
sion of a conductorand electrode for-contact with
multiple tube), and by providing a plurality of
the human flesh, the face of said electrode being
electrodes and switching means associated with
concave in form for containing a chemical sub
the electrodes and said input grids, I am able to
stancefor reducing the surface contact resistance
selectively associate any two of the electrodes
between said electrode and said ?esh or tissue.
with said input grids, the remaining electrodes
Other objects and advantages of the inven
all being connected together and grounded.
tion will be apparent to those skilled in the art.
3
2,409,033
In such an arrangement, the special selector
switch may have one arm connected to one of
the input grids and the other arm to the other
input grid. The switches may have ten posi
tions for ten electrodes. The switches connect
said grids to any two selected electrodes and si
multaneously connect the remaining eight elec
trodes together and to the ground.
_
The switch arms when rotated from one posi
trodes will presently be described~the magnitude
of the contact resistance through the skin is of
the order of 3,000 to 15,000 ohms. This low con
tact resistance has the further advantage of per
mitting the operation of the ampli?er without
appreciable disturbance by the thermal agitation
of electrons in the ohmic resistance comprising
the input circuit.
The grids, in the input stage
tion to another short-circuit adjacent contact 10 of the ampli?er, are connected to ground through
resistors of the order of 100,000 ohms, thereby
points while bridging the spaces therebetween.
in effect further limiting the maximum imped
The grids are never "free” and cannot receive
ance across which an interfering ?eld may build
large signal voltages which might temporarily
up a voltage.
paralyze the ampli?er.
A shield is provided between the primary and
In order that a clear understanding of the elec
the secondary windings of the power transfor
trical properties of the human body may be had,
mer, and the power cord leading from said pri
the following should be borne in mind: If the
body were a perfect conductor according to Fara
day’s laws, all parts of the surface would be of the
same potential, and it would, therefore, be im
possible for my new and improved electroenceph
alograph device to detect upon it any differences
in potential resulting from action currents.
Were the body a perfect insulator, any poten
tials developing within it could not be led off and
recorded by a device having ?nite input imped
ance.
As a matter of fact, the body is a poor
conductor, therefore potentials developing there
in at various points can be led off by surface elec
trodes to a system having input impedance of 3 O
comparable or larger magnitude.
Adjacent and more distant portions of the body
act as an antenna capacitively coupled to near
by conductors, such as power lines, electrical ap
paratus, etc, and pick up interfering voltages
which are conducted through the body to the
lead-off electrodes of the recording system.
In order to drain off to ground a substntial
portion of the charges induced by such coupling,
the electrodes not connected to the system are
grounded either separately through a multiplicity
of resistive paths or all directly.
Interference from electro-static ?elds is further
reduced by placing the patient upon a com
paratively thin mattress or cushion which rests
in turn upon a grounded conducting metal table
or a conducting bed-spring. This increases the
capacity between the body and earth or ground
and therefore reduces the potential induced in
the body by any given strength of electro-static
mary to a lighting circuit outlet is also shielded.
The grounding system is designed so as to avoid
loops in which an interfering electro—magnetic
?eld might build up a large circulating current and
across parts of which an interfering voltage might
therefore develop. I have found that a ground
line made as follows is very effective: A ?exible
wire ending in a clip and forming a part of the
subject’s electrode harness is effective, particu
larly when the clip is connected to the metal of
the bed spring or to the metal of the examining
table. This ?exible wire is also connected to the
ampli?er case. From its point of arrival inside
the case, the wire runs as directly as possible
to the cathode of the ampli?er tubes in the ?rst
stage. All other grounds within the ampli?er
circuit are made either to this wire or to the case
or chassis. The shield of the power-cord may
be connected to this wire or to a grounded point
within the ampli?er case and at the end where
the power-cord plug enters the lighting circuit
socket the shield is connected to another ?exible
wire carrying a clip which is connected to a wa
ter-pipe ground.
Further means are also employed in my new
and improved apparatus to reduce interference;
for example, it will be noted that the cathodes
of the two triodes in the first stage are connected
directly to ground without any bias resistor.
These tubes operate with no grid-bias. By di
rectly grounding these cathodes, any potential
which might be induced upon them by capacity
coupling through the heater insulators from the
?eld.
heaters, which are operated on raw alternating
As a further step in the reduction of interfer
ence, the ampli?er operates on a push-pull prin
current, is eliminated. This arrangement also
eliminates potentials due to ohmic leakage
through imperfections in the heater insulators.
In the subsequent stages of the ampli?er, how
ciple and therefore the potential differences be
tween the grids will be ampli?ed, while the po- ..
tentials induced by the above-mentioned capaci
tive coupling affects both grids equally and with
the same polarity and will not be ampli?ed.
In this speci?cation, the differences in poten—
tial between the grids will be termed “potentials .;
which are out of phase with each other,” “po
tentials which are out phase with one another,”
or "bio-electric potentials.” Potential changes
upon both grids in the same direction or polarity
will not be ampli?ed, and these potentials will
be termed "potentials in phase with each other,”
“potentials in phase with one another,” or “in
terfering potentials.” The means by which this is
accomplished will be presently described.
To reduce the interference pick-up as much as *
possible, contacts established with the surface of
the tissue are of a minimum feasible resistance,
thereby substantially reducing the impedance
across which an interfering ?eld may build up a
voltage. With the electrodes used—which elec
ever, the cathodes are biased by means of bias
resistors and capacitative and ohmic leakage is
therefore balanced as far as possible, for exam
ple by the expedient of grounding a mid~point
of a resistor of 100 ohms bridging the heaters.
In the plate supply of the ?rst and second
stages of the ampli?er, I have introduced a volt
age regulator tube which is effective in the re
moval of 60 cycle or 120 cycle ripple from the
?lters following the recti?ers, and it is also ef
fective in an even more essential capacity in
maintaining constant plate voltage for these
stages.
This is very necessary and important be
cause relatively small plate supply voltage
changes would be ampli?ed by the system, and,
therefore, would appear as interfering signals in
the third and fourth stages, and these interfering
signals may be of sufficient amplitude to block
the ampli?er.
The residual 60 cycle interference from power
2,409,033
lines is ?ltered out by a ?lter. choke introduced
between the third and fourth stages.» lv have
found that it is preferable to place the ?lter in
this position in the circuit because here the sig
nal strength is large enough not to be over-ridden
by the hum picked up by the inductance ele
ments from the power supply chokes and the
power transformer, and also the hum component
of the signal at this point is not large enough
to run the ampli?ers oif their linear character
istics and thus modulate the action~current sig
nal.
would be conducive to enormous degeneration
effects, but I prefer to use the circuit arrange
ments herein described.
In the last stage of the ampli?er, the push
pull arrangement herein shown is responsive to
only those. signals which are out of phase with
each other, and signals which are in phase with
each other have no e?ect whatever.
It is believed that a better understanding of the
10 action will be had from the following explana
The reason that a low-pass ?lter may be used
at. all is due to the fact that the characteristic
frequencies. of the electroencephalogram signals
lie sufficiently below 60 cycles for a ?lter to dis
criminate between said signals and the hum
without seriously distorting the wave shape of
the signals, (60 cycles being the frequency of the
power supply).
Now it is evident that the two active electrodes
of the subject or patient will pick up potentials,
and that these potentials, if of bioelectric origin,
will be different from each other in phase be
cause the electrodes are situated over di?erent
groups of cells. Interfering voltages, however,
such as those proceeding from commercial fre-.
quency electrostatic ?elds, will tend to affect the
entire semi-conducting substance of the body
simultaneously, and therefore the interfering I
voltages as picked up by the electrodes will be in
tion of the action of the unbalanced in-put sig
nals. These signals pass through the ?rst stage
of the ampli?er with substantially no change in -
form other than their amplitude. For example,
if a positive signal is delivered to one grid only
of the ?rst tube in the ?rst stage, and no signal
is‘ impressed upon the grid of the second tube in
the. ?rst stage, an ampli?ed negative signal will
result on the ?rst grid of the second stage, and
no signal with reference to ground on the second
grid of the. second stage. Now the negative sig
nal on the second grid in stage two, reduces the
cathode current for this tube. The cathodes, be
ing tied together, will simultaneously go nega
tive in voltage.
Since however, grid. two of stage two remains
at ground potential, this means that cathode two
will go negative with respect to its former
quiescent potential relative to grid two. There
fore, as far‘ as tube two is concerned, grid two
has received the equivalent of a positive signal;
therefore, plate-current two will increase and in
phase with each other.
the output circuit the signal delivered to the‘ next
In the ?rst. stage of the ampli?er, which is a
stage will not only show a positive ampli?ed volt
simple resistance-capacity coupled circuit, no
age appearing on grid one of stage three, but
discrimination or differentiation. between either I"
also a negative and somewhat smaller voltage on
type of potentials or signals referred to hereinbe
grid two of stage three. The process repeats
fore is attempted. In the second stage, however,
until
at the end of the cascade the plate-currents
it will be noted that neither the cathode-resistor
in
the
two tubes making up the fourth stage show
nor the-screen supply resistor are by-passed. As
long as the incoming signals from the first stage 40 very nearly equal and opposite changes in spite
of the fact that the input signal has been applied
are equal and opposite (symmetric and out-of
to one side of the ampli?er. The screen circuits
phase with each other) the cathode and screen
of the pentode stages act to enhance this e?ect.
currents in each tube will change by equal and
It will be borne in mind that the selector
opposite amounts and there will be no net change
in the total cathode and screen currents of the
pair.
Assuming, however, that there are ‘also po
switches when set for any two given electrodes, '
at the same time ground the other eight elec
trodes and‘ the ‘latter are therefore inactive.
These eight electrodes are obviously more or less
tentials in phase with each other reaching both
short-circuited together by the action of the
grids, it will be obvious that this voltage will af-,
fect both the screen and the cathode currents 50 switch, but the algebraic sum of their potentials
is a. de?nite quantity with respect to the
in the same direction, and thereby produce a
algebraic sum of the potentials of the two active
change in the cathode and screen voltage which
electrodes. The action currents originating
will tend to degenerate. or reduce the last men
beneath these eight inactive electrodes are im
tioned potentials. This continues on in the third
and fourth stages with the result that while the 55 pressed all in- the same phase upon both input
grids simultaneously. However, the ampli?er
signals which are out of phase with each other
degenerates these signals and they do not appear
are ampli?ed more and more, the signals which
at all in the oscillogram record.
are in phase with each other are relatively am
My new and improved electroencephalograph
pli?ed less and less. The e?ect is further en
device,
referring now to Figure 1, is housed in a
hanced by using resistors in the cathode circuits 60
metal case 23’ which has hinged thereto a cover
as large as possible, consistent with keeping the
2!. A suitable lock 2?. is provided for securing
operation of the tubes on a linear characteristic.
the
cover in its closed. position. The top panel
Since no tubes except those in the last stage re
23. is secured in position in the metal case 28 by
ceive signals large enough to operate them over
of screws 24. Removably mounted in the
an appreciable percentage of the total linear 65 means
panel is a record carrying a feeding device gen
plate characteristic, the cathode-resistor and
consequently the grid~bias may be made much
v erally designated by the numeral 25, which will
presently’ be described in detail particularly in
larger than would be possible were it necessary
connection
with Figures 3. '7, 8, and. 9.
to obtain full plate swing in all of the stages.
The controls and the recording head carried‘
It will be noted that in the circuits of my de 70
on the panel 23 will be described in connection
vice I do not employ the obvious subterfuge of
with the circuit diagram in Figure 10.
using greater cathode-resistors and compensat
The circuit is more or less conventionally shown
ing for the excessive grid-bias produced by the
in Figure 10, and the grids of the input tubes
use of a negative voltage supply on its grounded
end. Of course the use of such an expedient 75 29, 2-1, are extended and connected to switching
2,409,033
devices; the ‘grid of the tube 26, for example, is
connected to the switch-arm 28 of the switch 29,
and the grid of the tube 21 is connected to the
switch-arm 30.
Leads from the switch 29 are connected to a
socket 32 mounted on the panel 23. This socket
has contacts corresponding to all ten of the
switch positions, and in addition has a ground
connection so that when a plug, such as the
plug 33, is ‘plugged into said socket, connections
8
bias cell 4| and a push-button key 42. With the
switches in this position, the key 42 may be de
pressed to record a standard, as will hereinafter
be described.
When the switches are turned to the “12” posi
tion, which is marked “Cortex" on the panel 23,
the grids of the tubes 26 and 2'! are connected to
a jack 43, so that when a plug 44 is inserted in
this jack, said plug being connected to a cortical
are made to all ten of the leads in the cable 34—
electrode 45, which will presently be described,
the shielding 35 on the cable is at the same time
the contacts of the cortical electrode are directly
connected to said grids.
connected to ground. This cable, as well as the
one shown in Figure 13. will presently be de
When the plug. is inserted in the jack 43, the
scribed.
15 contact arms '16, 41, are moved away from each
The switch 29 is in effect a two-gang switch,
other and away from the contact arms 48, 49,
respectively, which are connected together and
and in one gang the contact arm 28 establishes
contact with contact points to which the leads to
to ground. In other words, the jack contacts 46
the socket 32 are connected. These leads are
and 47 are normally connected together and to
extended to the outside rim 29a of the second 20 ground until the plug is inserted.
gang of the switch, and leads from the contact
The cathodes of the the two triodes in the input
points of the ?rst gang of the switch 3| are con
stage, it will be noted, are connected directly to
nected to the inside rim 29b of the second gang
ground without any bias resistor. The ?lter
of the first switch.
chokes between the third and fourth stages re—
The rotor 29 is ganged to the switch arm 28, so 25 ferred to are designated by the numerals 50
and 5!.
that as the rotor 29c moves in unison with the
arm 28, points on the switch 3| are connected to
In the plate circuit of the ?rst and second
corresponding points of the switch 29. Ganged
stages of the ampli?er I have introduced a voltage
to the switch 3| is a second gang wherein the
regulator tube 52 for removingr the 69 or 120 cycle
outer rim 3|a is connected to the contact points
ripple from the ?lters following the recti?er and
on the inner rim 29b of the ?rst switch, and
for maintaining constant plate voltage on these
two stages.
wherein the contact points on the inner rim 1Hb
are connected to ground.
It will be noted that on the rotor 29° no bridg~
For controlling the sensitivity of the instru
ment, I have introduced a double potentiometer
ing contact appears in the position 36 (which in
designated as R8. The movable arms thereof are
the position shown represents a “7” position of
connected to the grids of the tubes 53, 54, in the
third stage. The shaft 61 of this double poten
the switch 29). It will also be noted that the
rotor 31 of the switch 3| has no bridging contact
tiometer carries a knob 68 which operates over
at the position 38 (which in the position shown
a graduated scale 69 on the panel 23 by means of
represents a “4” position of the switch 3|).
40 which the sensitivity of the device may be con
With the switches in the positions shown, the
trolled.
grid of the tube 2'1 is connected to the conductor
The resistance elements of these potentiome
4 in the cable, (to be presently described), and
ters are each grounded at one end, and the other
ends are capacitatively coupled to the plates of
the grid of the tube 26 is connected to the con
ductor '| in the said cable.
It will also be noted that the inner rim 3|b has
no ground connection at the vpoint 40; therefore,
the “7" switch point on 3| is not grounded, and
due to the absence of bridging connection at 38,
the "4” position on the switch stage 3|a is also
not grounded. However, all of the other switch
positions on the switch 3| are grounded.
Now. looking at switch 29, it will be seen that
the wire connecting the “7” position on the
switch 3| to the inner rim 2917 is not connected
to the position “7” on switch 29 due to the ab
sence of the bridging connection in the posi
tion 36. The result is that electrodes connected
to leads 1 and 4 (of the cable 34, Figure 1) are
directly connected to the input grids of the tubes
26 and 21, and all of the other electrodes are
grounded, and I may turn the switches 29 and 3|
to other positions to place the grids under the
in?uence of other electrodes at will, all other
electrodes than the pair selected being automati
cally grounded.
Although only ten points have been described
on the switches, they actually have twelve posi
the tubes 55, 56, in the second stage by means of
condensers C3, C4, respectively.
The tubes 51, 58, in the fourth or last stage
have their outputs connected to the moving coil
59 which drives the stylus 59, The ?eld struc
ture 6| of the stylus drive is excited by the wind
ing 62 which receives its current from the recti
her 63,
The stylus traverses the recording tape later
ally on a rotating drum 64 which is driven by a
synchronous motor 65 with suitable gear reduc
tion therebetween. A switch 66 has three posi
tions: (1) an “off” position; (2) a “ready” posi
tion; and (3) a “recording” position.
When the switch 66 is in the “ready” position,
the heaters in all the tubes are supplied with
current, but the exciting coil 52 is not energized,
nor is the synchronous motor 65 energized.
When the switch is in this position, the pilot light
which is green, lights up.
When the switch 66 is moved to the “record"
position, the circuits are energized, including the
exciting coil 62 and the synchronous motor 65;
the pilot light PR, which is red, also lights up,
and the pilot light PG is extinguished,
tions, as will be seen in Figure 10. When both
switch arms are positioned in the “11” position
(which is marked “Standard” on the panel 23),
the grids of the tubes 26 and 21 are connected to
carrying a spring clip 1 2 is secured to the shield
for connecting to a Water pipe or radiator. The
the standardizing circuit 39. This circuit includes
electrostatic shields 13, T4, are provided between
The power cord 70 is shielded and a wire 1|
5 series of resistors R19 to R22 inclusive, a grid 75 the primaries and secondaries of the power trans
formers.
aaoaosa
V
The following is a list of ‘the values of the com
ponents indicated on the circuit diagram:
R1 ____ohms__ 100,000 R24 _____ohms__ 2,000
Re
R3
R4
R5
____do____ 100,000
_____megohm'__ 1/2
_______ __do____ 1A;
_______ __do____ 1/2
.
R25
R26
R27
R28
____ “do-..” 6,000
____ __do____ 200
____megohm__ 1/2
____ohms__ 25,000
Re _______ __do____ 1/2
C1 __microfarad__
1
R7 _______ __do.____ 1/_>
C2
______ __d0____
1
Rs, dual
C3
______ __do____
1
potenti_
10
9 ..
-
C4
upon which is mounted a roller 90 which may
have a frictionless bearing between itself and said
shaft.
Spring means 9| urges the arm 89 in a
counter-clockwise direction, as viewed in Figure 7.
As may be seen in Figure 3, the free end of
the tape extends from the roll 83 underneath and
around the rotating drum 64 and across the ?at
mid-portion of the panel. This may also be seen
in Figure l. The roller 90 acts as a pressure roller
10 for holding the record in engagement with the
knurled surface of the rotating drum 64.
Referring now to Figure 9, the panel 23 has a
hole 92 formed therein. This hole may also be
seen in. Figure 7. A bracket 93 is secured to the
______ __do___a .02
15 panel 23 by means of screws 94 having nuts 95
______ __d0____ .02
on the bottoms thereof. Mounted on the bracket
______ _._d0______ .02
93 is a vertical plate 96. Mounted on the vertical
______ __do____ .02
plate 96 is an L-shaped member 91 and a second
______ _..d0____ .1
L-shaped member 98; the legs of the Us of these
_____ l_-_do__-_ 40
20 members face each other, thereby forming a slot
'_ _____ __do_l__
l
ometer ___do_ l/g-Vg
R9 _______ __do____ 1/2
C5 ______ __~do____
C6 ________d0____
1
1
R10 ______ __d0____ 1/z
R11 _____ __ohms__ 50
R12 ______ __d0_____ 50
C7
C8»
C9
R13 __-__megohm__ 1/2
C10
R14 ______ -_do____ 1/2
C11
R15
R16
R17
R18
C12
C13 ______ _fdo____ 60
C14 ______ __do____ 60
C15 ______ __d0____ 10
therebetween, the slot being designated by the
C16
C11
ter and form a working ?t in the slot 99.
___ohms__ 15,000
____do____ 750,000
_a__do____ 20,000
____d0_..__ 50,000
R19 _____megohms__ 3
R20 ____ __ohms__ 150
______ __do____ 15
______ __do____ 10
numeral 99. The panel 23 is notched to conform
to the slot '99 so that the vertical arm 18 may en
V
In threading up the tape, the free end 832
R21 _______do____ 150
C18 ______ .._d0____ 15
should project to the right from off the top of
R22 _____megohms__ 3
C19 ______ __d0____ 5
the reel, as seen in Figure 7 ; ?rst holding the free
R22 ____ohms__ 50,000
end of the tape on the reel to prevent it from
unwinding, place the arm 18 (which may be
L1—2220 henries; 2B and 21 Type 6F5; 52-VR
150-30
30 termed a slide) in the slot 99 between the guides
L2-2220 henries; 55 and 56 Type 6SJ7; V1o~—5Z4
L3-—i5 henries; “53 and 54 Type 6SF5; V11--6X5
L1~l5 henries; 51 and 58 Type 6P6; 63-5T4.
I do not wish to be bound by these values as
they are merely given by way of example, and it
must be distinctly understood that many changes
made in the values of these components in the
circuits may be made without departing from the
91, 98, and lower the panel partially. Then draw
the free end of the tape underneath the rotating
drum 64 and bring it around the drum and un
derneath the stylus 60, which may be lifted to
facilitate the operation. Then carry the free end
of the tape to the left, as viewed in Figures 3 and
9, underneath the roller 90 and over the ?at sur
face of the panel 16. Now lower the panel 16
until it comes in contact with the panel 23, taking
spirit of the invention.
‘
40 up the slack of the tape while doing so by drawing
A fuse 15 is connected in series with one side
it toward the left. When the tape is properly
of the line feeding the primaries of the power
threaded, it will have the appearance shown in
transformers.
This fuse is mounted in a cup
shaped holder which projects downwardly from
Figure 1.
With the cable 34 connected to the machine by
inserting the plug 33 in the socket 32, the ten
cap which may be unscrewed for replacing blown
conductors having metallic disc electrodes I00
fuses.
connected thereto, are by this operation con
In connection with the recording device 25, the
nected to the switches 28 and 30, and the cable
carrying the ground clip [01 is connected to
panel 16, preferably formed of insulation, has
secured thereto a bracket 17 (see Figures 7 and 50 ground by means of the side lug I02 on the plug
8) and a vertical arm 18 is secured to the bracket
33. The disc electrodes are numbered 1 to 10, in
11 in any suitable manner, for example by means
clusive, corresponding to the switch positions 1
of the rivets T9. The vertical arm 18 has a por
to 10, inclusive.
tion 80 thereof extending above the surface of
In attaching these disc electrodes to the scalp,
the panel 70, and a hole 8! is formed therein to 55 the operation is facilitated if the subject is seated
facilitate the removal of the panel and its con
in a chair. For routine exploration, the follow-~
tents from the machine, as will hereinafter be
ing scheme may be adopted:
described.
Electrode:
A spindle 82 projects laterally from the arm
# 1. Left frontal
18 and serves as a support for a roll 83 of record 60
I 2. Right frontal ~
tape. Suitable downwardly depending rods 84
3. Left parietal
and 65 are mounted on the panel 16 and serve to
4. Right parietal
align and guide the tape 83a toward the rotating
5. Left occipital
drum 24. The panel 16 has a notch 85 formed
6. Right‘ occipital
therein to accommodate the rotating drum 64 65
‘ 9. Lobe of left ear
which is provided for feeding the tape at a uni
'1 0. Lobe of right ear
form rate past the recording stylus 80.
Electrodes
#7 and #8 are placed in the vicinity
The rotating drum 64, as hereinbefore pointed
of any area from which other neurological signs
out, is driven by a synchronous motor through
.
suitable gearing, and is of such diameter that 70 are suspect. I
The electrodes are placed in contact with the
the speed of the record tape past the stylus is
scalp and collodion of a fairly heavy consistency
exactly three centimeters per second.
is applied to the skin and to the edges of the
A boss 8‘! mounted on the panel 16 carries a
electrodes with a medicine dropper. The drying
stud 88 upon which an arm 89 is pivotally mount
ed. On the end of the pivoted arm 89 is a shaft 75 of the collodion is greatly accelerated by means
the panel 23 like a well, and is covered with a
11
2,409,033;
of a current of warm air from an ordinary elec
tric hair dryer.
The electrodes may be held ?rmly in contact
with the skin by means of a pencil point or an
orange stick held in contact with the concave de
pressions in the surfaces of the electrodes until
the collodion sets. When the electrodes are se
cured in place, the patient is transferred to an
a
12
have been placed in the neighborhood of sus
pected lesions or other areas of particular inter
est. Then records are taken between various
pairs of electrodes on the scalp, additional ones
being applied if necessary, in order sharply to
delineate any focus of unusual electrical gravity.
For these readings both selector switches are of
course used to connect the amplifier to any pair.
examining table or cot-bed, and a low pillow may
Never place arm 28 and arm 30 both on the same
be placed under the patient’s head. The cot or
electrode number.
examining table may have a thin pad mattress
Set the sensitivity control 68, to begin with, at,
and the ground clip Hll should be connected to
say, “70” on its scale 69. Wait an additional few
the examining table or cot. If painted, the paint
seconds for the ampli?er again to become sta
should be scraped off so that the clean metal
bilized.
to metal contact is established between the 15
Now turn the starting switch 66 to “Record."
ground clip and the metal of the examining table
The red panel lamp PR will now light and the
or the springs of the cot.
It is thoroughly advisable, particularly for the
tape draw-off motor will start feeding the tape
"33a and the stylus 60 will begin to draw a black
beginner, to make an electrical test of the resist
line on the paper. If the tape begins to feed
ance of the electrode contacts, because the ap 20 crookedly, return the switch 66 to “Ready,” pull
paratus cannot function if there is a broken or
the free end of the tape to straighten, then switch
poor contact in the path of a current from the
to “Record” again. The stylus 60 will move side
brain to the ampli?er. The resistance of the elec
wise, recording the electroencephalogram. The
trode contacts is measured between any two elec
stylus is electri?ed when the starting switch is
trodes and should average between 3,000 ohms to
on “Record” and will give a slight unpleasant
a maximum of not more than 15,000 ohms. A
shock if touched.
higher resistance than this limit would have the
twofold effect of reducing the sensitivity of the
apparatus and of permitting extraneous inter
ference to get into the ampli?er and obscure the
record.
If a higher resistance is noted between any
If the tracing is not wide enough-that is, has
not enough amplitude to give a clear recognizable
and easily analyzed graph-very slowly increase
the sensitivity by turning the knob 68 toward 100
on scale 69. If on the other hand, the stylus
vibrates with such a great amplitude that it hits
pair of electrodes, the defective member of the
the internal stops at the ends of its limits of
pair may be determined by checking each one
travel, reduce slowly the sensitivity to obtain a
separately with another electrode known to have 35 suitable tracing. Notations on the leads used,
good contact. The electrode with the defective
experimental conditions, or events of interest can
contact is then taken off and carefully re-applied.
be made directly in pencil on the tape.
Before applying any electrodes to the scalp, a
To record from other leads, ?rst stop the record
material for reducing the surface contact resist
ance may be rubbed into the scalp. All stray 40 by turning the starting switch back to “Ready."
Then change the‘lead switches to the next pair
wires and other apparatus should be removed
of electrodes selected. Wait a few seconds for
from the vicinity of the patient and no person
stabilization of the ampli?er before turning back
should touch. the patient or approach within
to “Record.”
three feet of the patient during a recording.
At the conclusion of the test, remove the elec
Make sure that the tape 83a can run freely over 45
trode tips from the jack and take the electrodes
the motor drum 64 and that it comes off to the
from the head of the subject by softening the
left straight and smoothly across the Bakelite
collodion with acetone. Clean the electrodes by
panel 16; pull it lightly to be certain that all slack
underneath the panel is taken up.
washing with alcohol or ether to dissolve the
Make sure that the stylus 60 is at rest in the 50 collodion and with water to remove any traces of
center of the paper. If it stays at one side, push
dried electrode paste. Store the electrodes care
fully by fastening them again to the card on
it over hard enough so that when it is released
it will remain in the middle.
which they are shipped or by hanging them from
Turn the starting switch 66 to “Ready.” The
a notched board attached to the wall so that the
green panel light PG will show that the ampli- 55 wires will not become tangled.
fler is turned on, and that the tubes are warming
In different areas and in different subjects,
up. Allow them three minutes to become stabi
there is awide variation in the amplitude of the
lized before attempting to record.
waves found. It is, therefore, necessary, as (ii
For a routine examination by a method now
rected above, to adjust the sensitivity of the re
coming to be accepted as standard the procedure 60 cording mechanism to obtain graphs which, on
is to make records of the left frontal, parietal,
the one hand, must be large enough to analyze
and occipital areas with respect to an indifferent
and which, on the other hand, must be small
electrode, and the same for the right side. To
enough to be recorded within the limits of Width
obtain these records with the selector switch, set
of the tape. It is desirable, however, to know at
arm 30 on 9 while arm 28 is placed successively 65 all times the absolute magnitude of the waves
on electrodes 1, 3, and 5, then set arm 30 on 10,
7 being recorded.
while arm 28 is placed on electrodes 2, 4, and 6.
By this means the indifferent electrode, which is
in contact with the lobe of the ear, is on the same
To ?nd this, for any setting of the sensitivity
control 68, turn the starting switch 66 to “Ready,”
then set arm 28 and arm 30 both on “Standard."
side of the head as the active electrodes, with 70 Wait a few seconds, then turn the starting switch
the result that some cross potentials from deeper
66 back to “Record.” Now depress and release
structures are eliminated in the recording.
the black button 42 marked “Standardize.” The
The procedure outlined gives records of what
stylus 60 will make a vertical mark upwards when
are known as resting potentials. Further records
should be taken with electrodes 7 and 8, which 75 the button is depressed and back again when
the button is released. The length of this verti
2,409,0ser
l3?
calf line upwards is the response of the stylus‘
to a 50 microvolt signal.
It is also essential to note the speed of the tape
in order that the frequency of the waves may be
computed. In this’ instrument, the speed is ?xed
at exactly 3 centimeters per second. Time rela
tions may instantly be found by measuring the
I4?
plug has a hole I3I formed ‘therein which forms
a socket to receive the head of the electrode, and
spring members I32 are provided for reducing
the contact resistance between the plug and the
head.
The headset may be applied to the subject, and
the curved members III, II2, adjusted to desir
able positions and secured by means of the thumb
tape with a common. metric ruler.
nuts H3, and the electrodes may be applied to
Special electrodes are available for taking elec
trocorticograms from the exposed cortex at op 10' any desired combinations of tap holes Hi]: after
which the plugs it") may be connected to the
eration under'sterile conditions, for taking elec
electrodes and the socket I23. plugged in. The
tromyograms from single muscular units, for tak
procedure may follow‘ the procedure. described
ing gross electromyograms from the surface of
above in connection with the. cable 34‘.
the skin over the skeletal. muscles, etc. To use
The recording mechanism includes four’ pole
15
these-electrodes, set both arm 28 and arm 30 at
pieces
and the powerful direct current electro
positions marked “Cortex” and plug the special
magnet 62 energizes these pole pieces. The mov
electrode plug ?lllvinto the jack marked 43, “Corti
ing armature coil is wound in two sections, and
cal electrodes.”
both are placed over the armature so that ity is
The cortical electrode 65 includes a- holder Hi3,
magnetized virtually by the algebraic sum of the
the outer end I-M of which has a socket formed
two currents of the two coils; one coil is placed
therein so that the electrode I65 per so may be
in the: plate circuit of the output tube 51, and the
removed or inserted at will, thereby permitting
other is placed in the circuit of the output tube
the electrode to be properly removed and
58. The direct current plate components ?ow
sterilized before being placed in contact with the
through these coils in such a direction that the
tissue. The end of the electrode includes a
magnetic fields cancel. The coils are wound to
grounded or “shield” area I86 surrounding the
the correct load impedance for the output tubes.
active or central core IN. The entire electrode
The armature is returned to its central posi
cord may also be sterilized.
tlon
by a pair of very strong phosphor-bronze
In Figures 11 to 14, inclusive, another electrode
helical
tensionv springs, with the result that the“
and cable arrangement is shown. A‘ head-set,
recording mechanism has exceedingly high e?i
generally designated by the numeralv H38, in
ciency and develops relatively enormous power.
cludes a head band £59 which may be somewhat
oval in form and larger than the average head.
A plurality of tapped holes Ilil is vtermed in the
band we enabling the operator to position the
scalp electrodes, which will presently be described,
in a verylarge number of combinations of po
sitions. Pivotally secured to the band» its are
curved members III, I.I2, which also contain a
plurality of tapped holes HQ; The means for
pivotally securing the members Ill, H2, to the
band I88 are thumb screws [It whichenable the
operator to. set the pair of members lII, H2, in
any desired position with respect to each other
and. with respect to the band I99.
The electrodes, one of which is shown enlarged
in Figure 14, consist of of a bushing IIrl having
a hole therethrough which forms a working ?t
with a shank H5. The bushing also includes an
"The condenser Cls'an'd resistor R28 supply crit
ical damping to they moving element. of the re
cording mechanism.
*
The armature shaft‘ is. vertical, and at the top
of. this shaft is a steel cross-head (not shown)
which carries the stylus 60 by a right-angle ex
tension of the latter which passes through the
, head horizontally. The stylus is therefore moved
through a horizontal are by the vibrations of the
armature, but is held in contact with the record
83a by a helical torsion spring which urges it ver
tically downwardly.
The stylus is maintained at a positive poten-~
tial byuthe transformer ‘M and its associated
recti?er and ?lter system, the current passing
through the limiting resistor R23 to the stylus.
The passage of the current produces an imme-~
outer threaded surface I I6 which ?ts the threaded 50 diately visible and permanent record on the pre
pared electro-chemically sensitive tape 83*‘. This
holes Ilii. The shank H5 carries a head which
current‘ is turned on simultaneously with the cur
has a groove H8 formed therein and the end H9
rent to the motor 65' and. the current to the field
is rounded to permit the easy application of a
plug thereto, which plug will. presently be de
scribed.
82 by moving switch 66 to position “Record.”
Condenser C11 s'erves‘to eliminate radio interfer
ence caused by arcing to the stylus point. This’
On. the other end of the shank H5 is an elec
recording system, without electri?cation of the
trode I20, the end IZI of which is concave to
stylus, is suitable for use with ‘a. prepared. waxm
contain a material for reducing the contact re
covered tape'
sistance between’ the electrode and the scalp. A
A shield I33 having an angular portion I35 is0->
spring.’ I22 extends from the left end of the bush 60
lates the ?rst three ampli?er stages from the
ing, as viewed in Figure 14, to the electrode I20
fourth stage, the recti?ers and the. recording
and urges the electrode to the left (which would
devices. The shield I34 joins the shield I33 and
be toward the scalp when the headset is in po
is positioned between the recti?ers and the re
sition on the patient) .,
Referring now to Figure 13, the plug I231 is like 65 cording device.
I‘. have also made electroencephalographs for
the plug 33 previously described, and includes ten
multi-channel work which employed a, plurality
contact pins I124 which fit the socket 32, and a
of ampli?ers (as many ampli?ers as channels de
ground lug I25 establishes a ground contact with
sired). Figure 15 shows an arrangement for a.
thev chassis. The cable I26 is covered with a
shielding I21, and‘ the shielding and the ground
elip I23 are connected to the ground lug I25. The
ends of the‘ wires of the cable carry tabs 129
which’ bear numbers corresponding to the posi
tionsofv the’ switches 28, and 30. Each conductor.
has-secured to the end thereof a plug. I3.EI.- This 75.
multi-channel electroencephalograph, portions of
the ampli?er being omitted to avoid duplication.
In this arrangement the multi-point switches
employed have seventeen points and siXteen- ac
tive positions, the seventeenth point being con
nected to ground. <
~
2,409,033
15
16
The switches in channel I are designated by
mean potentials which are out-oI-phase with
the numerals I36 and I31, and the switches in
each other or which are of opposite phase, as the
channel II are designated by the numerals I38
device deals with potentials which are primarily
and I39. The midpoint of the switch I36 is con
picked up by not less than two active electrodes on
nected to the grid of the input tube 261’, and the
a biological preparation. One end of the group
midpoint of the switch I31 is connected to the
of cells in the biological preparation may be
grid of the input tube 21‘). The input tubes 26b
negative with respect to the other end of the
and 21'’ are exactly like the input tubes 26 and
same group when a bio-electric potential is being
21 shown in Figure 10, and the balance of the
circuit associated with the tubes 26” and 21b is 10 picked up by the electrodes.
The term “potentials in phase with each other,"
exactly like the circuits associated with the tubes
“potentials in phase with one another," or “in
26 and 21 in Figure 10, and therefore they need
terfering potentials” used herein is taken to
not be repeated in Figure 15 or further described.
mean any extraneous or interfering potentials,
In channel II the midpoint of the switch I38
such as static, both man made and natural. It
is connected to the grid of input tube 26c and the
will be appreciated that the bio-electric potentials
midpoint of the switch I39 is connected to the
are very small and that all interfering potentials
grid of the input tube 27°, the rest of the ampli
are very great in comparison thereto.
?er also being like that shown in Figure 10.
It will be evident from a study of the above
The stylus controlled by the channel I and the
speci?cation that I construct my ampli?er so
stylus controlled by the channel II are placed
that each stage therein tends to cancel out inter
side by side in reasonably close spaced relation
fering potenials and at the same time to amplify
to each other. The tape used with the two sty
bio-electric potentials (potentials which are out
luses is substantially wider than the tape 83“;
of phase with one another or with each other)
also the rotating drum is likewise Wider than the
and that as a means of catching and shoving out
rotating drum 64; but the driving arrangement is
any interfering potentials which have not been
identical to that shown at 65 in Figures 3 and 4.
previously balanced out or which are instituted
In Figure 15 a further modi?cation is shown,
in the ampli?er itself, I provide ?lter chokes be
which modi?cation may likewise be applied to
tween the output of the next to the last stage
the single channel electroencephalograph herein
and the ?nal stage.
before described. Instead of short-circuiting and
Although I have herein shown and described
grounding the switch contacts not in use, and
by way of illustration 9, device for producing elec
thereby grounding the electrodes to which they
troencephalograms which obviate the necessity
are connected, this shorting feature may be
for shielding the instrument and/or the patient by
omitted and the switch contacts may all be con
means of a “Faraday cage” or the like, said device
nected to ground through resistors.
In multi-channel devices, I have successfully
employed resistors for this purpose each having
also being capable of making electrocardiograms,
I do not wish to be bound by the exact arrange
ments and the speci?c values of elements herein
a resistance of 100,000 ohms. This results in a
shown and described, as it is obvious that many
large number of parallel grounded resistors, and
the ?nal effect in interference suppression is 40 changes may be made in the apparatus shown
without departing from the spirit of the invention
found to be substantially the equivalent of the
as set forth in the annexed claims.
shorting arrangement shown in Figure 10.
What is claimed is:
Another advantage is that with this arrange
1. In a device for making recordings of po
ment the switches are simpler and therefore less
expensive and less liable to get out of order.
tentials generated in the human brain, a multi
In Figure 15, I have shown the leads running Jr. stage push-pull ampli?er, a plurality of contact
members, means to hold said contact members
from the switches as terminating in individual
in predetermined or de?nite positions in con
binding posts, but it is obvious that these could
tact with the scalp of a patient, switching
be connected to sockets in the manner shown in
Figure 10.
means, conductors for connecting said contact
1:: members to said switching means, connections
The device herein described may also be used
between said switching means and the control
as an electrocardiograph, in fact it is believed
grids of the ?rst stage of said ampli?er, said
to be the only device ever built which will suc
switching means being adapted to selectively con
cessfully produce an electrocardiogram not re
nect said grids to any two of said conductors
quiring photographic development for the pres
‘ and to ground all of the other conductors,
ervation of the record. Notwithstanding anal
shielding means surrounding said conductors and
yses which indicate the desirability of a fre
connected to ground potential, a metallic table or
quency range up to at least 240 cycles per sec
the like for supporting said patient, a thin in
ond, my device turns out, even with the ?lters
sulating pad between said table and said patient,
described in the circuit, very creditable records.
means for connecting said support to ground
By cutting out the ?lters, I obtain a higher fre
potential :thereby reducing the impedance of
quency range which admittedly is advantageous.
In using the apparatus as an electrocardio
graph, it is merely necessary to position the elec
trodes to pick up heart potentials instead of brain
potentials. When the device is used as an elec
trocardiograph, the grounding of the electrodes
is not necessary in view of the fact that the
amplitude of the electrocardiogram is so much
greater than that of the electroencephalogram
that the precautions of hum ?ltering and ground
ing of additional electrodes are entirely unneces
sary.
‘
said tissue and leading off interfering potentials
to ground, and a recording device connected to
the output of said ampli?er for recording poten
' tials picked up by said contact members from
said patient after the same have been ampli?ed.
2. In an electroencephalograph, a panel, an
ampli?er beneath said panel, a recording device
including a motor-driven drum, a recording tape
embracing said drum in driven relation thereto,
a stylus carried on said panel in contact with the
tape on said drum, said stylus being motivated
by the output current of said ampli?er; and a,
In this speci?cation and in the appended claims,
the term “bio-electric potentials” are taken to 75 control switch on said panel having a first posi
tion wherein all circuits are “dead,” a second po
2,409,033
‘
17
sition wherein the heaters of the tubes in said
ampli?er are supplied with energy, and a third
position wherein said ampli?er is rendered fully
operable and ‘the motor for driving said drum is
supplied with energy for moving said tape past
said stylus.
3. In an electroencephalcgraph, in combination,
a head-set including a substantially rigid oval
18
to- ground and other non by-passed resistors in
series with the screen grids of said several stages
for causing bio-electric or out-of-phase poten
tials to :be ampli?ed and for effecting the nulli
?cation or balancing out of in-phase‘ or interfer
ence potentials, means for connecting said ampli
?er to a source of alternating current, ?lter
choke means connected between the output of
one of said stages and the input of the next suc
band having a plurality of tapped holes formed
therein in spaced relation to each other, at least 10 ceeding stage for deleting interference poten
tials which the previous stages have failed to
one arcuate member being pivotally supported on
balance out, together with interfering potentials
said band and also carrying a plurality of spaced
originating in the ampli?er itself and the alter
tapped holes, a plurality of electrodes adapted to
nating current hum, recording means connected
be selectively positioned in any of said tapped
holes and each being comprised of a scalp-engag 15 to the output of said ampli?er, a panel, a pair
Of multi-c'ontact switches on said panel con
ing member, a shank, and a terminal end, said
nected to the input tubes of said ampli?er, a
shank carrying a spring and a threaded bushing
plurality of shielded conductors connected to the
having threads to match said tapped holes, said
contacts of said switches, means for connecting
spring being so positioned on said shank as to
urge its scalp-engaging member into resilient 20 said cables to sources of bio-electric or out-of
phase potentials, and connections between
contact with ‘the scalp, and a cable connected to
ground potential and said switches, said last
said electroencephalograph and carrying sockets
connections being arranged to ground all of the
engaging said terminal ends.
contacts on said switches except one on each
4. In an electroencephalograph, in combina
tion, a head-set including a substantially rigid 25 switch, whereby a single selected contact on each
switch may be ungrounded and connected to one
oval band having a plurality of tapped holes
of the input tubes of said ampli?er.
formed therein in spaced relation to each other,
rI. In an electroencephalograph, a multistage
a plurality of arcuate members pivotally con
push-pull
thermionic ampli?er including resis
nected to said band and each also carrying a plu
rality of spaced tapped holes, whereby said arcu 30 tors and capacitors interconnecting the tubes of
said stages and non by-passed resistors connect
ate members may be given any desired positions
ing
the cathodes in several of said stages directly
with respect to each other and to said band,
to ground and other non by-passed resistors in
means to clamp said arcuate members in any de
series‘ with the screen grids of said several stages
sired positions; a plurality of electrodes adapted
for'causing bio-electric or out-of-phase poten
to be selectively positioned in any of said tapped
tials to be ampli?ed and for effecting the nulli
holes, and each being comprised of a scalp-en
?cation or balancing out of in-phase or inter
gaging member, a shank, and a terminal end, said
ference potentials, means for connecting said
shank carrying a spring and a threaded bushing
ampli?er to a source of alternating current, ?lter
having threads to match said tapped holes, said
spring being so positioned on said shank as to 40 choke means connected between the output of one
of said stages and the input of the next suc
urge its scalp-engaging member into resilient
ceeding stage for deleting interference potentials
contact with the scalp; and a cable connected to
which the previous stages have failed to balance
said electroencephalagraph and carrying sockets
engaging said terminal ends.
out, together with interfering potentials origi
5. In an electroencephalograph, a multistage 45 nating in the ampli?er itself and the alternating
current hum, recording means connected to the
push-pull thermionic ampli?er including resist
output of said ampli?er, a cortical electrode in
ors and capacitors interconnecting said stages
cluding a central electrode surrounded by a
and non-by-passed resistors included in circuits
with the cathodes and screen grids of several 50 grounded, shielded area, both being positioned
in, contact with brain tissue, said central elec
of said stages themselves for causing bio-electric
trode being adapted to be influenced by brain
as out-of-phase potentials to be ampli?ed and
potentials, conductors connected to said cortical
for effecting the nulli?cation or balancing out of
electrode and to the input tubes of said ampli
in-phase or interference potentials, means for
connecting said ampli?er to a source of alter 55 ?er, and a shield about said conductors and con
nected to ground potential.
nating current, ?lter choke means connected be
8. In an electroencephalograph, a multistage
tween the output of one of said stages and the
push-pull thermionic ampli?er including resis
input of the next succeeding stage for deleting in
tors and capacitors interconnecting the tubes in
terference potentials which the previous stages
have failed to balance out, together with inter 60 said stages and non by-passed resistors connect
ing the cathodes in several of said stages directly‘
fering potentials originating in the ampli?er it
to ground and other non by-passed resistors in
self and the alternating current hum, a pair of
series with the screen grid circuits of said several
multi-contact switches connected to the input
stages for causing bio-electric or out-of-phase
tubes of said ampli?er, a plurality of conductors
potentials to be ampli?ed and for effecting the
connected to said switches, whereby the inputs 65 nulli?cation
or balancing out of in-phase or in
of said tubes may be selectively connected to any
terference potentials, said ampli?er also includ
two of said conductors and bi0~electric or out-of
ing resistors between the input grids of the ?rst
phase potentials carried by any combination of
stage of said ampli?er and ground potential for
two of said conductors selected by said switches
limiting the impedance across which interfering
may be delivered to the input of said ampli?er. 70
6. In an electroencephalograph, a multistage
push-pull thermionic ampli?er including resis
?elds may build up voltages, at ?lter choke be
tween the input of the last stage and the output
of the next preceding stage for deleting inter
tors and capacitors interconnecting the tubes of
ference potentials which the preceding stages
said stages and non by-passed resistors connect
have failed to balance out, together with inter
75
ing the cathodes in several of said stages directly
19
2,409,033
fering potentials originating in the ampli?er it
self, recording means connected to the output of
said ampli?er, a shielded cable having a plurality
of conductors positioned on a biological prepara
tion, selective switching means connected to said
20
ternating current hum, and recording means con
nected to the output of said fourth stage.
11. In an electroencephalograph, a multi-stage
push-pull ampli?er, a plurality of contact mem
bers, means to hold said contact members in pre
determined or definite positions in contact with
ductors whereby different sources of bio-electric
animal tissue, switching means, conductors for
or out-of-phase potentials may be delivered to
connecting said contact members to said switch
said grids, and shortcircuiting means included in
ing
means, connection between said switching
said switching means for grounding all said con 10
means and the control grids of the ?rst stage of
tacts except the ones connected to said grids.
said ampli?er, said switching means being
9. In an electroencephalograph, a four stage
adapted to selectively connect said grids to any
push-pull ampli?er including a power pack for
of
said conductors, shielding means surrounding
amplifying potentials which are out of phase with
said conductors and connected to ground poten
each other and for nullifying potentials which 15 tial,
the two tubes in said ?rst stage including
are in phase with each other and termed inter
cathodes which are directly connected to ground
fering potentials, means for connecting said am
potential thereby placing them intermediate the
pli?er to a source of alternating current, con
potentials on said control grids, a metallic table or
nections between the control grids of the ?rst of
the like for supporting said animal tissue, an in
said stages and a source of potentials which are 20 sulating pad between said table and said animal
out of phase with each other, means for shielding
tissue, means for connecting said support to
grids and having contacts connected to said con
said connections from interfering ?elds, resist
ground potential thereby reducing the impedance
ance bridges from said grids to ground potential
for limiting the impedance across which interfer
ing ?elds may build up voltages, means for main
taining constant plate voltages on said ?rst and
the second of said stages, thereby preventing
plate voltage changes which would be ampli?ed
and appear as interfering signals in the third and
fourth stages, at least one of said stages includ
ing two anodes, two cathodes, two control grids
and two screen grids, said control grids being
capacitively coupled to the anodes of said ?rst
stage, said cathodes and said screen grids employ
ing non by-passed resistors, ?lter chokes between ;
said third and said fourth stages for ?ltering out
alternating current hum, and recording means
connected to the output of said fourth stage.
10. In an electroencephalograph, a four stage
push-Dull ampli?er for amplifying potentials
which are out of phase with each other and
termed bio-electric and for nullifying potentials
which are in phase with each other and termed
interfering potentials, a power pack for said am
pli?er, means for connecting the same to an al
ternating current power line, shielded conductors
connected to the control grids of the input stage
of said ampli?er and to a source of bio-electric
potentials, terminals on said cables and included
in the connections to said source, means for re
ducing the contact resistance between said ter
minals and said source, resistance bridges from
said control grids to ground potential for de?ning
the maximum impedance across which interfering
?elds may build up voltages, means for maintain
ing constant plate voltages on said ?rst and the
second of said stages, thereby preventing plate
voltage changes which would be ampli?ed and
of said tissue and leading off interfering poten
tials to ground, said ampli?er including at least
other stages each employing two anodes, two
cathodes, two control grids and two screen grids,
said control grids being capacitively coupled to
the anodes of the preceeding stage, said cathodes
and said screen grids employing non by-passed
resistors for minimizing any tendency for changes
to occur in the values of the net total cathode and
screen currents when potentials which are out
of phase with each other and termed bio-electric
potentials are impressed on the grids of said ?rst
stage, the cathode and screen currents in each
stage both being adapted to be affected in the
same direction when potentials which are in
phase with each other and termed interfering
potentials are impressed across the grids of said
40
?rst stage whereby said ?rst mentioned potentials
are ampli?ed and said last mentioned potentials
are degenerated or reduced, and a recording
device connected to the output of said ampli?er
for recording potentials picked up by said contact
members from said tissue after the same have
been ampli?ed.
,.
12. In an electroencephalograph, a multistage
push-pull thermionic tube ampli?er including re
sistors and capacitors interconnecting said stages,
at least two of said stages including screen grid
tubes having their cathodes connected to ground
potential through non by-passed resistors and
having their screen grids connected through non
by-passed resistors to the high potential source
in said ampli?er for causing potentials respec
tively opposite to each other in phase impressed
on the input of said ampli?er to be ampli?ed, and
for effecting the nulli?cation or balancing out of
appear as interfering signals in the third and
fourth stages, others of said stages each includ 60 potentials which are in phase with one another,
said ampli?er also including ?lter choke means
ing two anodes, two cathodes, two control grids
between the output of one of said stages and the
and two screen grids, said control grids being ca
input of the next succeeding stage for deleting
pacitively coupled to the anodes of said ?rst stage,
those
of said last mentioned potentials which the
said cathodes and said screen grids employing
preceding stages failed to balance out, together
non by-passed resistors for diminishing the tend
with other interfering potentials also in phase
ency for changes to occur in the net total cathode
with
one another and originating in the ampli?er
and screen currents when said bio-electric poten
itself, recording means connected to the output
tials are impressed on the control grids of said
of said ampli?er, and shielded conductors for
?rst stage, the said cathode and screen currents
leading said potentials that are respectively op
both being affected in the same direction by said
posite to each other in phase to the input of said
interfering potentials impressed across the grids
of the input stage, ?lter chokes between said
third and said fourth stages for ?ltering out al
ampli?er,
LOVE'I'I‘ GARCEAU.
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