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Differences in sensory and motor cortical organization following brain injury early in life.

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Differences in Sensory and Motor Cortical
Organization Following Brain Injury
Early in Life
Gary W. Thickbroom, PhD,1 Michelle L. Byrnes, PhD,1 Sarah A. Archer, MSc,1 Lakshmi Nagarajan, MBBS,2
and Frank L. Mastaglia, MD1
There have been a number of physiological studies of motor recovery in hemiplegic cerebral palsy which have identified
the presence of novel ipsilateral projections from the undamaged hemisphere to the affected hand. However, little is
known regarding the afferent projection to sensory cortex and its relationship to the reorganized cortical motor output.
We used transcranial magnetic stimulation (TMS) to investigate the corticomotor projection to the affected and unaffected hands in a group of subjects with hemiplegic cerebral palsy, and also performed functional magnetic resonance
imaging (fMRI) studies of the patterns of activation in cortical motor and sensory areas following active and passive
movement of the hands. Both TMS and fMRI demonstrated a normal contralateral motor and sensory projection between the unaffected hand and the cerebral hemisphere. However, in the case of the affected hand, the TMS results
indicated either a purely ipsilateral projection or a bilateral projection in which the ipsilateral pathway had the lower
motor threshold, whereas passive movement resulted in fMRI activation in the contralateral hemisphere. These results
demonstrate that there is a significant fast-conducting corticomotor projection to the affected hand from the ipsilateral
hemisphere in this group of subjects, but that the predominant afferent projection from the hand is still directed to the
affected contralateral hemisphere, resulting in an interhemispheric dissociation between afferent kinesthetic inputs and
efferent corticomotor output. The findings indicate that there can be differences in the organization of sensory and
motor pathways in cerebral palsy, and suggest that some of the residual motor dysfunction experienced by these subjects
could be due to an impairment of sensorimotor integration at cortical level as a result of reorganization in the motor
system.
Ann Neurol 2001;49:320 –327
Observations in humans and experimental animals indicate that the cerebral cortex has the ability to adapt
to injury of the nervous system through a range of
mechanisms that include changes at a cellular level,
functional reorganization of intact cortical areas, and
the unmasking or formation of new pathways.1–7 The
relative importance of these mechanisms varies with
age, and in particular the potential for large-scale functional reorganization, for example the formation of
novel pathways, appears to be associated with brain injury early in life, such as occurs in cerebral palsy8 –10 or
with developmental abnormalities such as in subjects
with congenital mirror movements.11
Cerebral palsy results from perinatal lesions or
anomalies in the developing brain affecting the motor
cortex and pathways, and the condition is commonly
classified according to the motor abnormality that is
present.12 There have been a number of physiological
studies of motor recovery in hemiplegic cerebral palsy
which have identified the presence of novel corticomotor pathways, including ipsilateral projections from the
undamaged hemisphere to the affected hand, arising
from either branched or unbranched fibers originating
in the undamaged hemisphere.8 –10,13
Whereas cerebral palsy is classified according to motor dysfunction, sensory abnormalities are often present
and may contribute to motor disability.14 However
there have been relatively few physiological studies of
the afferent projection to sensory cortex in hemiplegic
cerebral palsy. Studies of somatosensory-evoked potentials following peripheral nerve stimulation have shown
a greater degree of variability on the affected side15 or
From the 1Center for Neuromuscular and Neurological Disorders,
University of Western Australia, Australian Neuromuscular Research
Institute, Western Australian Institute for Medical Research, Queen
Elizabeth II Medical Center, Nedlands; and the 2Department
of Neurology, Princess Margaret Hospital for Children, Subiaco,
Australia.
Address correspondence to Dr Thickbroom, Center for Neuromuscular and Neurological Disorders, University of Western Australia,
Australian Neuromuscular Research Institute, Queen Elizabeth II
Medical Center, Nedlands WA6009, Australia.
E-mail: gthickbr@cyllene.uwa.edu.au
Received Jun 19, 2000, and in revised form Sep 15. Accepted for
publication Sep 19, 2000.
320
© 2001 Wiley-Liss, Inc.
delayed or absent evoked potentials.14 Those studies
have suggested that there can be abnormalities in the
central processing of afferent information; however, it
is not known whether there are ipsilateral components
to the sensory projection to the cortex and how this
might correlate with the presence of an ipsilateral corticomotor projection to the hand. We hypothesize that
there may in fact be differences in sensory and motor
organization in subjects with cerebral palsy confined to
one hemisphere, and that this could be a factor contributing to the reduced motor abilities on the affected
side in these subjects.
In the present study, we used transcranial magnetic
stimulation (TMS) to investigate the properties of the
corticomotor projection to the affected and unaffected
hands in a group of subjects with hemiplegic cerebral
palsy, and compared the results with functional magnetic resonance imaging (fMRI) studies of the pattern
of activation in motor and sensory cortical areas following active and passive movement of the hands. In
that way, we were able to to investigate the kinesthetic
afferent projection from the hand to sensory cortical
areas in each cerebral hemisphere and relate the findings to the presence of contralateral and/or ipsilateral
cortical efferent projections to the hand.
Methods
Subjects
With ethics approval from the University of Western Australia (subjects ⬎18 years of age) and Princess Margaret Hospital for Children (subjects ⬍18 years of age), 7 subjects (4
males) suffering from hemiplegic cerebral palsy gave informed consent to participate in the study. Subject details are
provided in Table 1. All subjects were studied as adolescents
or as adults (15 to 57 years of age) and had some degree of
functional motor ability in their affected hand; however, the
degree of motor disability was variable. In four cases there
was a history of difficulties or complications at birth, and the
brain injury was thought to have occurred in the perinatal
period. In the other three (Cases 1, 4, and 7) the cerebral
palsy was first apparent after the age of 3 months and was
thought to be compatible with either perinatal or antenatal
insult. None of the cases was thought to have suffered acute
insults in the neonatal period. Two subjects (Cases 1 and 2)
had epilepsy and were receiving anticonvulsant medications
at the time of the study (see Table 1). Motor function was
assessed by the Motor Assessment Scale.16 Upper arm function was normal in all subjects (6/6); however, all subjects
had some degree of loss of hand movement (4/6) and a more
severe disability on the advanced hand assessment (0/6 to
2/6). Tactile, pain, and vibration sense were normal in the
affected hand in all but one subject who had a mild impairment of tactile sensibility and two subjects who had increased sensitivity to light touch or pinprick. All seven subjects had impaired stereognosis and/or graphaesthesia and
two-point discrimination in the affected hand, and four of
seven had impaired joint position sense (see Table 1). None
had tactile or visual inattention on clinical testing. Subjects
had an identifiable abnormality on MRI scanning: four
porencephaly, one periventricular leukomalacia, and two capsular or corona radiata lesions (see Table 1). TMS and fMRI
investigations were carried out on separate occasions. When
appropriate, results were related to normative TMS and
fMRI data described previously.17,18
Motor Cortex Stimulation
Surface electromyographic (EMG) recordings were made
from electrodes over the motor point and the metacarpophalangeal joint of the abductor pollicis brevis muscle of each
hand. EMG signals were amplified (⫻1000) and bandpass
filtered between 20 and 2 kHz before being digitized at 2
kHz for 500 milliseconds following each stimulation. Studies
were carried out during a monitored low-level contraction of
the target muscle.
Transcranial magnetic stimulation was delivered using a
MAGSTIM 200 stimulator (Whitland, Dyfed, UK) with a
5-cm-diameter figure-of-eight coil. The coil was held tangential to the skull and aligned in the parasagittal plane with the
handle posterior. The junction of the coil was held over the
site to be stimulated.
The presence of contralateral and ipsilateral corticomotor
projections to the affected and unaffected hands was investi-
Table 1. Subject Details
MAS Score
Sensory
Case Age
Affected Mirror
No. (years) Sex Hand
Movements UAF HM AHA Pass. S/G 2-Pt. Magnetic Resonance Imaging
1a
2a
3
4
5
6
7
57
15
18
17
20
16
32
F
M
M
M
M
F
F
L
R
L
R
R
L
L
⫹
⫹⫹
⫹
⫹⫹
⫺
⫺
⫺
6
6
6
6
6
6
6
4
4
4
4
4
4
4
0
0
0
0
2
2
2
a
n
a
n
n
a
a
a
a
a
a
a
a
a
a
n
a
a
a
a
a
Porencephalic cyst, R centrum semiovale
L Porencephalic cyst
R Frontal porencephalic cyst
L Porencephalic cyst
L Periventricular leukomalacia
R Posterior capsular lesion
Encephalomalacia, R centrum semiovale
a
Patients with epilepsy receiving anticonvulsant medication (carbamazepine and sodium valproate, respectively). Mirror movements ⫽ presence
of coactivation with movement of either hand: ⫹⫹ ⫽ strong coactivation; ⫹ ⫽ coactivation; ⫺ ⫽ no coactivation. MAS score ⫽ motor
assessment scale: upper arm function (UAF), hand movements (HM), and advanced hand function (AHA); a score of 6 indicates normal
function. Sensory: Pass. ⫽ sense of passive movement of fingers; S/G ⫽ stereognosis/graphaesthesia; 2-Pt. ⫽ two-point discrimination: a ⫽
abnormal; n ⫽ normal.
Thickbroom et al: Motor and Sensory Reorganization in Cerebral Palsy
321
gated. With recording from each hand, scalp sites were explored over each hemisphere (in a 1-cm grid) to determine
whether a motor-evoked potential (MEP) could be detected
in the target muscle. Stimulus intensities of up to 100% of
stimulator output were used when necessary.
When an MEP could be detected at ⬍100% of stimulator
output, motor threshold was measured by delivering groups
of four stimuli at progressively increasing stimulus intensity
(in 5% steps) until an MEP could be detected with three of
the four stimuli. Four stimuli were then delivered at an intensity of 20% of stimulator output above threshold and the
mean peak-to-peak MEP amplitude and latency from stimulation to MEP onset were calculated.
Functional Magnetic Resonance Imaging
Functional imaging was carried out on a 1.5-T Siemens
Magnetom Vision Plus scanner equipped with gradient overdrive and echo-planar imaging (EPI) capabilities. Imaging
was performed using a standard head coil with 2202 mm
field of view and a 1282 image matrix. Subjects lay in the
supine position with the head held steady using a bitemporal
clamp. The anterior and posterior commissures (AC, PC)
were identified from a set of three sagittal slices. Ten 5-mmthick axial slices that lay parallel to the AC-PC line, the first
slice tangential to the superior surface of the brain, were selected for functional imaging. Functional imaging was carried out using a blood oxygen-level–dependent gradientrecalled echo-planar sequence (90° pulse, TE ⫽ 66
milliseconds). Each experimental run consisted of a group of
six sets of images (each set constituting 10 slices) collected at
3-second intervals during an 18-second period of rest followed by a further six sets acquired during a period of activation, with the rest-activation cycle repeated five times, resulting in a total of 60 image sets (30 in the active state and
30 at rest). For each group of six sets, the first two sets were
removed from the analysis to allow for the delay in the fMRI
signal, leaving 20 sets of data for the rest and activation periods. Functional images were generated for each slice by first
identifying significantly activated voxels using Student’s t test
comparing the rest and active conditions on a voxel-by-voxel
basis ( p ⬍ 0.01, t ⬎ 2.5, 19 degrees of freedom) and then
forming a functional image of the magnitude of the differ-
ence in the mean signal between the activation and rest
phases for each significantly activated voxel (see also references 18 –20). The interhemispheric fMRI signal was compared by measuring the number of significant voxels in a
region of interest drawn over each hemisphere so as to encompass primary sensory and motor cortices and secondary
parietal sensory cortex. This region included activity immediately anterior to the central sulcus, within the central sulcus and immediately posterior to the central sulcus (primary
motor and sensory cortex), and activity posterior to the primary sensorimotor cortex (secondary sensory areas). FMRI
data were superimposed upon the average of the 60 images
collected during each study, which served as the anatomical
reference image.
For the motor task, subjects performed movements of the
affected hand which were selected according to the degree of
residual motor function. In some subjects, this consisted of
finger/thumb opposition movements, whereas in other subjects only opening and closing of the hand or wrist movement was possible. The rate of movement was also selected
according to the speed with which subjects could comfortably perform those tasks. In the case of movement of the
unaffected hand, a simple finger/thumb opposition task was
used for all subjects, performed at a rate of ⬃1/sec. Subjects
were encouraged to move only the hand under study; however, in some cases there was also more proximal movements,
even with movement of the unaffected hand. Subjects practiced the movements before recording, with movement timing paced by an investigator. Subjects were observed in the
scanner by the investigator who documented the pattern of
body movements and the rate of execution of the task.
In the passive movement protocol, subjects were instructed to relax fully, and an investigator passively moved
the hand at a rate of ⬃1/sec. In the case of the affected
hand, the passive movement was varied according to the
movement that the subject performed during the voluntary
movement recording, and consisted of either extension or
flexion of the index finger or wrist. The same passive movement was used for the unaffected hand. The investigator held
the subjects’ hand throughout the recording and moved the
hand during the activation cycles.
Table 2. Transcranial Magnetic Stimulation (TMS) Data for Affected and Unaffected Hands
Affected Hand
Unaffected Hand
(Unaffected Hemisphere)
Case
THR
LTY
AMP
1
2
3
4
5
6
7
60
55
70
50
55
50
65
20
20
19.5
21
19
20.5
19
5.8
5.5
4.3
5.2
5.5
5.7
7.8
Affected Hemisphere
Unaffected Hemisphere
THR
LTY
AMP
⫺
⫺
⫺
⫺
70
80
80
⫺
⫺
⫺
⫺
19.5
20
19
⫺
⫺
⫺
⫺
2.0
2.2
4.3
THR
LTY
AMP
60
55
70
50
55
50
65
20
20
19.5
20.5
19
20
19
1.8
7.3
2.3
5.1
2.4
6.1
4.1
Motor threshold (THR) is presented as percentage of stimulator output, MEP latency (LTY) in milliseconds, and amplitude (AMP) in mV. ⫺
⫽ no response. No TMS response was observed in the unaffected hand with stimulation of the affected hemisphere. Normal range (⫾2
standard deviations, 20 controls, contralateral projection): THR (40% to 70%); LTY (17.1 to 24.4 ms); AMP (1.5 to 15.1 mV).
322
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Table 3. Functional Magnetic Resonance Imaging Data for Active (Act) and Passive (Pass) Protocols
Unaffected Hand
Unaffected Hemi
Affected Hand
Affected Hemi
Affected Hemi
Unaffected Hemi
Subject
Act
Pass
Act
Pass
Act
Pass
Act
Pass
1
2
3
4
5
6
7
35
44
NA
170
NA
NA
NA
22
21
77
183
66
71
20
13
6
NA
57
NA
NA
NA
0
2
6
30
10
3
0
NA
7
NA
NA
NA
NA
127
43
2
145
79
47
41
12
NA
38
NA
NA
NA
NA
0
0
0
0
3
0
4
0
Number of active voxels obtained from primary sensory and motor cortex and secondary parietal sensory cortex for each hemisphere and hand.
NA ⫽ not analyzable.
Results
The results are summarized in Tables 2 and 3. In the
following description of the results, the unaffected
hemisphere is defined as the hemisphere contralateral
to the unaffected hand, and likewise for the affected
hemisphere.
Motor Cortex Stimulation
In all subjects an MEP with normal latency and amplitude was recorded from the unaffected hand with
stimulation of the unaffected hemisphere, and no response was obtained from this hand with stimulation
of the affected hemisphere. The motor threshold
ranged from 50 to 70% of stimulator output, MEP
amplitude ranged from 4.3 to 7.8 mV, and MEP latency was 19 to 20.5 milliseconds.
In four subjects (Subjects 1 to 4) (Table 2), no response could be recorded from the affected hand with
stimulation of the affected hemisphere even at 100% of
stimulator output; however, an MEP could be recorded
from that hand with stimulation of the unaffected
hemisphere, with a motor threshold of 50% to 70%
(Fig 1, Case 4). These subjects all demonstrated large
porencephalic cysts. In the remaining three subjects, a
response could be recorded from the affected hand
with stimulation of either the affected or unaffected
hemisphere (Fig 1, Case 7); however, the threshold to
stimulation was lower with stimulation of the unaffected hemisphere by 15% to 30% of stimulator output (see Table 2). In all cases, the MEP threshold for
the affected and unaffected hands with stimulation of
the unaffected hemisphere was the same, as were the
optimal scalp site, MEP latency (mean 19.7 milliseconds vs 19.9 milliseconds) and MEP amplitude (mean
4.2 mV vs 5.7 mV).
Functional Magnetic Resonance Imaging
With voluntary movement of the affected hand, a reliable fMRI signal could be recorded in only two subjects (Cases 2 and 7) (Fig 2 and Table 3) owing to
Fig 1. Motor-evoked potential (MEP) waveforms obtained
from the unaffected hand with stimulation of the unaffected
hemisphere, and the affected hand with stimulation of the
affected and unaffected hemispheres, for Cases 4 and 7. Case
4: similar amplitude MEPs for both hands with stimulation
of the unaffected hemisphere, no response from the affected
hand with stimulation of the affected hemisphere. Case 7: an
MEP was recorded from the affected hand with stimulation of
either the affected or unaffected hemispheres.
head movement artifact associated with movement of
proximal muscles during the task. In Case 2 there was
greatest activation in the unaffected hemisphere with
movements of either the unaffected or affected hand.
On the basis of the TMS recordings, that subject had
an exclusively ipsilateral corticomotor projection to the
affected hand from the unaffected hemisphere. In Case
7, fMRI activation was located in the affected hemisphere with movement of the affected hand. With
TMS, that subject demonstrated a bilateral projection
to the affected hand from both the affected and unaffected hemispheres; however, the motor threshold was
lower with stimulation of the unaffected hemisphere.
Similarly, a reliable fMRI response could be recorded
Thickbroom et al: Motor and Sensory Reorganization in Cerebral Palsy
323
Fig 2. Functional magnetic resonance imaging (fMRI) data
from Cases 2 and 7 during voluntary movement of their affected hand (the affected hemisphere has been outlined). Case
2: fMRI activation in the hemisphere ipsilateral to the affected
hand. Case 7: fMRI activation in the hemisphere contralateral
to the affected hand. Images shown in a radiological reference
frame (left hemisphere on the right).
only in three subjects during movement of the unaffected hand (Cases 1, 2 and 4) (see Table 3). In those
subjects the fMRI signal was greatest in the unaffected
hemisphere.
Passive movement yielded an fMRI response in all
but one subject. With passive movement of the unaffected hand, the expected pattern of activation was observed in the primary sensory cortex and secondary parietal sensory regions of the unaffected hemisphere.
Likewise, with passive movement of the affected hand,
an fMRI signal was detected only in the affected hemisphere, with no consistent activation in the unaffected
hemisphere (Fig 3 and Table 3). Thus, for both the
affected and unaffected hand, passive movement induced activation in sensory cortical areas on the side
contralateral to the passively moved hand.
Discussion
In this group of cerebral palsy subjects, we found normal patterns of TMS and fMRI results associated with
the unaffected hand, with a contralateral corticomotor
projection demonstrated by TMS, and maximal activation in the hemisphere contralateral to the unaffected
hand with both the active and passive fMRI protocols.
However, in the case of the affected hand, the motor
threshold with TMS was lowest with stimulation of the
hemisphere ipsilateral to this hand, whereas passive
movement resulted in activation of the contralateral
hemisphere. These results demonstrate that there is a
significant fast-conducting corticomotor projection to
the affected hand from the ipsilateral hemisphere, but
that the afferent projection is directed to the contralateral hemisphere, resulting in a dissociation between the
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Annals of Neurology
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hemispheres receiving kinesthetic inputs and providing
motor outputs.
The TMS results are consistent with previous reports
which demonstrated the presence of fast-conducting ipsilateral corticomotor projections to the affected hand
in subjects with hemiplegic cerebral palsy.8 –10,13 On
the basis of correlation studies of single unit firing patterns, it is believed that these projections can result
from either abnormally branching corticospinal neurons or unbranched fibers originating in the undamaged hemisphere.8 The present observations that the
optimal site, motor threshold, MEP latency, and MEP
amplitude are the same for both the ipsilateral projection to the affected hand and the contralateral projection to the unaffected hand are also consistent with
branched or unbranched fibers directed to the affected
hand from corticospinal neurons originating in the
hand area of the undamaged hemisphere. The 4 subjects in whom the corticomotor projection to both
sides originated purely in the unaffected hemisphere all
had large porencephalic cysts in the affected hemisphere, whereas a dual ipsilateral and contralateral projection to the affected hand was observed in the remaining cases with less extensive subcortical lesions
(Fig 3). Thus, the size and location of the lesion, as
well as the level of maturity of the system at injury, are
probable factors in determining the degree of interhemispheric reorganization of cortical motor control.
Reliable motor fMRI activation maps could not be
recorded in all subjects, even with movement of the
unaffected hand. This was due to excessive movement
artifacts associated with the performance of the task.
However, even with good motor activation maps, a
number of factors still need to be considered when interpreting such maps in hemiplegic cerebral palsy, including (1) the confounding effect of coactivation of
the affected and unaffected hands during intentional
activation of either hand; (2) the possibility that even
when subjects were able to suppress their coactivation
there could be motor cortex activity associated with
this effort; and (3) the fact that voluntary movement
will also activate primary sensory cortex, which is located on the posterior bank of the central gyrus in
close proximity to primary motor cortex and could be
confused with motor activation. As a result, we used
the TMS findings to unambiguously define the origin
of the fast-conducting corticomotor projection to the
affected and unaffected hands in the present study. In
this way, TMS and fMRI were used in a complementary
manner to delineate the motor and sensory cortices.
Nevertheless, a reliable fMRI signal could be measured with voluntary movement of the affected hand in
two subjects. In one of those subjects, activation was
maximal in the unaffected hemisphere during movement of either hand, supporting the TMS findings of a
corticomotor projection to each hand from the unaf-
Fig 3. Functional images from four consecutive transverse slices for all subjects during
passive movement of their affected hands.
The affected hemisphere has been outlined.
In all cases fMRI activation was located in
the affected hemisphere (the hemisphere
contralateral to the affected hand). Images
shown in a radiological reference frame
(left hemisphere on the right).
Thickbroom et al: Motor and Sensory Reorganization in Cerebral Palsy
325
fected hemisphere. In the second subject, voluntary
movement of the affected hand was associated with activity only in the contralateral hemisphere, whereas
TMS demonstrated a bilateral corticomotor projection
to that hand, with a lower motor threshold for the ipsilateral projection. It may therefore be the case that
despite having a greater excitability with TMS, the ipsilateral projection is not always the functionally more
important projection in situations where there remains
a weak contralateral projection, and that the residual
contralateral projection could in fact be important for
certain hand movements, such as fractionated finger
movements (see also below).
Passive movement can activate the three types of
sensory inputs to the cortex: cutaneous afferents, muscle afferents, and joint receptors21–24; and both functional imaging studies and evoked potential recordings
have demonstrated cortical activation associated with
passive movement.25–28 The relative contribution of
these receptors to the fMRI response in the present
study cannot be determined, because we chose to use a
natural and easily applied passive movement protocol
that would be comfortable to the subjects, rather than
a technique designed to activate a particular class of
receptor. Previous functional imaging studies using
fMRI and positron emission tomography demonstrated
that the regions from which a signal could be detected
are similar with both active and passive movement protocols of this type.27,28
The fMRI response with passive movement was invariably located in the affected hemisphere: that is, in
the hemisphere contralateral to the passively moved
hand. In contrast, the TMS results indicated that there
was either a purely ipsilateral projection to the affected
hand from the unaffected hemisphere, or a bilateral
projection (from both hemispheres) in which the ipsilateral pathway had the lower motor threshold and was
thus more easily excited. Thus, the results indicate that
the dominant or more excitable motor pathway to the
affected hand originates in the unaffected hemisphere,
whereas it is the affected hemisphere that receives kinesthetic input from this hand.
These results are most easily explained on the basis
that whereas there has been extensive motor reorganization in these subjects, including the presence of novel
ipsilateral motor pathways, there has not been a corresponding sensory reorganization of kinesthetic sensory
inputs from the affected hand, with preservation of the
normal contralateral sensory projection. In a previous
mapping study of two subjects with congenital mirror
movement, a normal scalp topography was also demonstrated for the somatosensory evoked potential in the
presence of clear ipsilateral motor pathway demonstrated by TMS,11 further supporting the dissociation
of motor and sensory representations.
Proprioceptive sensory feedback is of fundamental
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March 2001
importance in the execution of voluntary movement of
the hand.29 Information from muscle receptors is conveyed to multiple motor and sensory areas of the brain,
including motor areas 4 and 6, and sensory areas 3a, 1,
and 2.30 Interruption of sensory input results in impaired perception of limb position and reduced accuracy of movement.31 In the present subject group, it
appears that processing of kinesthetic sensory information and motor commands associated with the affected
hand may take place in different hemispheres, and it is
possible that this dissociation could contribute to some
of the motor dysfunction experienced by those subjects. Our data also suggest that a remnant of the normal contralateral corticomotor projection to the affected hand could be important to aspects of fine hand
movement, as this projection could have greater access
to sensory information from the affected hand. This
hypothesis has some support from the findings in the
subject for whom fMRI activation during voluntary
movement was confined to the affected hemisphere, in
the presence of a bilateral corticomotor projection
identified by TMS. In this situation, proximity of the
motor representation in the affected hemisphere to the
sensory representation of the affected hand may have
made the contralateral projection better equipped to
carry out the task. The importance of a residual contralateral projection in movement of the affected hand
is also supported by the fact that the worst MAS advanced hand function scores (0/6) were recorded for
the four subjects in whom a residual contralateral projection to the affected hand could not be detected with
TMS, and despite the presence of a strong ipsilateral
projection.
In conclusion, the present study has provided further
evidence for large-scale corticomotor reorganization in
subjects who suffer a brain injury early in life, in the
presence of a normally directed kinesthetic projection
to the affected hemisphere. The findings indicate that
there can be interhemispheric differences in the organization of sensory and motor pathways in cerebral
palsy, and suggest that some of the residual motor dysfunction in the affected hand could be due to a dissociation between the normal sensory and motor representations following motor reorganization.
The study was supported by the Medical Research Fund of Western
Australia.
Mr I. Morris, Chief Radiographer, Dr S. Davis, Chief Radiologist,
and radiographers at the Magnetic Resonance Imaging Unit, Department of Radiology, Sir Charles Gairdner Hospital, are thanked
for their support and for carrying out the functional imaging studies. Dr S. Ghosh is thanked for valuable comments. Ms K. Smith,
Department of Human Movement, University of Western Australia,
provided access to the subjects in this study.
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