Several PET or SPECT studies in normal subjects showed no significant activation of ipsilateral motor cortices during the performance of a standardised motor task despite a trend in some.' Nevertheless, recent studies with more subjects showed that the complexity of the task was correlated with a discrete but real activation of the ipsilateral cortices.
We personally found, using fMRI (Siemens Vision 15T), that in normal subjects the performance
of a unilateral motor task resulted in a bilateral activation of motor areas (unpublished
data). Activation of ipsilateral motor cortices has been shown many times in patients with acute neurological disease.
(Ipsilateral motor cortices are activated in patients with recovered vascular hemiplegia during the performance of a motor task and they may play a part in functional reorganization processes.
In 10 patients recovering from stroke, Palmer et al,31 using electromagnetic stimulations of the unaffected hemisphere, failed to show that in adults, recovery from stroke resulted from the emergence of ipsilateral fast conducting corticospinal pathways.
They showed that stimuli sufficient to excite the neurons of the fast conducting corticospinal pathway (short latency facilitation of contralateral biceps motor neurons) did not produce short latency depolarisation of motor neurons of the ipsilateral biceps.
The study of patients with mirror movements and with hemispherectomy provides us with some more arguments in favour of an oligosynaptic pathway.
Carr et al32 found evidence for reorganization of central motor pathways in 21 of 33 patients with hemiplegic cerebral palsy. The clinical and neurophysiological findings disclosed two different forms of reorganization according to the intensity of the mirror movements and to the onset of the motor deficit in life. Some patients with congenital hemiplegia had intense mirror movements and evidence
for bilateral fast conducting corticospinal pathways. Other patients with an acquired hemiplegia between 9 months and 7 years of age had weaker mirror movement. Magnetic stimulation of the healthy hemisphere induced the usual controlateral answer but also induced an ispsilateral evoked potential which occurred 4 ms later on average than the contralateral one. This ipsilateral answer was also smaller than the contralateral one. These results suggest that in this group another mechanism for mirror movement could be identified which could implicate an oligosynaptic
ipsilateral motor pathway even after maturation of the corticospinal tract. This pathway might participate in the recovery processes of acquired hemiplegia.
In a population of patients with hemispherectomy, Benecke et all3 found comparable results. The magnetic stimulation of the unaffected hemisphere provided both ipsilateral and controlateral potentials. The amplitudes of ipsilateral compound muscle action potentials roughly correlated with their individual residual motor capacities and showed a proximal-distal gradient. In patients with early brain damage the ipsilateral potential had short latencies and large amplitudes, whereas
patients with later acquired brain damage presented long latencies and small amplitude.
Comparable results were found in patients with a degenerated pyramidal tract.
Overall, these reports suggest that the reinforcement of the ipsilateral motor pathways may play a dominant part in the ipsilateral motor control of patients with brain damage.
The efficiency of this control seems to be greater when the lesion occurs early in life.
Our results provide some arguments to suggest that this ipsilateral motor control also exists at the beginning of the stroke even in the adult population.
A fuller characterisation of ipsilateral motor pathways remains to be achieved. Two main hypotheses need to be tested. A transcallosal inhibitory pathway disrupted on hemispheric lesion has been proposed by some authors. A twice crossed spinal tract was proposed by others 33-37 We suggest that ipsilateral deficit must be taken into account in the rehabilitation procedures.
This aspect needs to be tested precisely.
Several PET or SPECT studies in normal subjects showed no significant activation of ipsilateral motor cortices during the performance of a standardised motor task despite a trend in some.' Nevertheless, recent studies with more subjects showed that the complexity of the task was correlated with a discrete but real activation of the ipsilateral cortices.
We personally found, using fMRI (Siemens Vision 15T), that in normal subjects the performance
of a unilateral motor task resulted in a bilateral activation of motor areas (unpublished
data). Activation of ipsilateral motor cortices has been shown many times in patients with acute neurological disease.
(Ipsilateral motor cortices are activated in patients with recovered vascular hemiplegia during the performance of a motor task and they may play a part in functional reorganization processes.
In 10 patients recovering from stroke, Palmer et al,31 using electromagnetic stimulations of the unaffected hemisphere, failed to show that in adults, recovery from stroke resulted from the emergence of ipsilateral fast conducting corticospinal pathways.
They showed that stimuli sufficient to excite the neurons of the fast conducting corticospinal pathway (short latency facilitation of contralateral biceps motor neurons) did not produce short latency depolarisation of motor neurons of the ipsilateral biceps.
The study of patients with mirror movements and with hemispherectomy provides us with some more arguments in favour of an oligosynaptic pathway.
Carr et al32 found evidence for reorganization of central motor pathways in 21 of 33 patients with hemiplegic cerebral palsy. The clinical and neurophysiological findings disclosed two different forms of reorganization according to the intensity of the mirror movements and to the onset of the motor deficit in life. Some patients with congenital hemiplegia had intense mirror movements and evidence
for bilateral fast conducting corticospinal pathways. Other patients with an acquired hemiplegia between 9 months and 7 years of age had weaker mirror movement. Magnetic stimulation of the healthy hemisphere induced the usual controlateral answer but also induced an ispsilateral evoked potential which occurred 4 ms later on average than the contralateral one. This ipsilateral answer was also smaller than the contralateral one. These results suggest that in this group another mechanism for mirror movement could be identified which could implicate an oligosynaptic
ipsilateral motor pathway even after maturation of the corticospinal tract. This pathway might participate in the recovery processes of acquired hemiplegia.
In a population of patients with hemispherectomy, Benecke et all3 found comparable results. The magnetic stimulation of the unaffected hemisphere provided both ipsilateral and controlateral potentials. The amplitudes of ipsilateral compound muscle action potentials roughly correlated with their individual residual motor capacities and showed a proximal-distal gradient. In patients with early brain damage the ipsilateral potential had short latencies and large amplitudes, whereas
patients with later acquired brain damage presented long latencies and small amplitude.
Comparable results were found in patients with a degenerated pyramidal tract.
Overall, these reports suggest that the reinforcement of the ipsilateral motor pathways may play a dominant part in the ipsilateral motor control of patients with brain damage.
The efficiency of this control seems to be greater when the lesion occurs early in life.
Our results provide some arguments to suggest that this ipsilateral motor control also exists at the beginning of the stroke even in the adult population.
A fuller characterisation of ipsilateral motor pathways remains to be achieved. Two main hypotheses need to be tested. A transcallosal inhibitory pathway disrupted on hemispheric lesion has been proposed by some authors. A twice crossed spinal tract was proposed by others 33-37 We suggest that ipsilateral deficit must be taken into account in the rehabilitation procedures.
This aspect needs to be tested precisely.
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