Reorganisation of descending motor pathways in patients after hemispherectomy and severe hemispheric lesions demonstrated by magnetic brain stimulation

Abstract

Numerous clinical studies on patients after hemispherectomy (HS) have provided clear evidence that two distinct groups can be recognized on the basis of the quality of their motor functions after operation. One of these consists of cases where HS was performed after normal brain maturation, the other of patients where the removed hemisphere was damaged early in life. The postoperative motor function has been found to be much better in the latter group. In the present paper it is demonstrated that in contrast to normal subjects ipsilateral compound muscle action potentials (CMAPs) induced by magnetic stimulation of the one intact motor cortex are present in patients after HS. The amplitudes of ipsilateral CMAPs in the muscles roughly correlate with their individual residual motor capacities and show a proximo-distal gradient. In patients with early brain damage prior to HS, CMAPs had short latencies and large amplitudes, whereas in patients with later acquired brain damage prior to HS, CMAPs had long latencies and small amplitudes. It is suggested that reinforcement of the ipsilateral corticospinal pathway may be responsible for residual motor functions in patients with early brain damage, whereas in patients with later acquired brain damage cortico-reticulospinal pathways may play a dominant role in ipsilateral motor control.

Corticospinal tract atrophy and motor fMRI predict motor preservation after functional cerebral hemispherectomy

“…Although most corticospinal fibers decussate in the medulla to the contralateral corticospinal tract, an estimated 8.2% of motor function is relayed through ipsilateral corticospinal fibers. 1,36 Ipsilateral projections are suspected to play a role in the coordination of skilled movements in healthy subjects, possibly more so in the nondominant hand. The potential influence of the ipsilateral pathways is most robust in patients who have had a motor cortex stroke, and recent functional imaging studies support this concept of a subordinate collaborative motor pathway.…”

“…Several investigators have attempted to identify the cortical and subcortical regions associated with the neuroplasticity of motor function in patients who have undergone functional hemispherectomy. 1,20,[27][28][29][30] In addition to the primary motor cortex, associative cortical areasincluding the supplementary motor area (SMA), insula, inferior frontal cortex, occipital cortex, basal ganglia, and cerebellum-have been investigated as potential contributors to motor function preservation.…”

“…First, robust ipsilateral pathways are present at birth, representing an estimated 25% of descending uncrossed corticospinal fibers that contribute to the lateral and ventral corticospinal tracts. 1 Demand may then lead to increased ipsilateral tract utilization. Likewise, crossed inhibitory signaling from the contralateral hemisphere may lead to inhibition of the ipsilateral tracts in the preoperative state.…”

Influence of task-related ipsilateral hand movement on motor cortex excitability

“…Ipsilateral pathways are the only possibility in explaining recovery after hemispherectomy, and in explaining bilateral MEPs using TMS to the remaining hemisphere (Cohen et al, 1991;Benecke et al, 1991). The role of ipsilateral pathways was also suggested in recovery from stroke (Turton et al, 1996) and in patients with cerebral gliomas (Caramia et al, 1998).…”

Complex syntax in the isolated right hemisphere: Receptive grammatical abilities after cerebral hemispherectomy

“…Various aspects of sensorimotor and cognitive development following both right and left hemispherectomy have been reported in the literature [5][6][7][8]. The results have been found to vary, with the transfer of functions after hemispherectomy seeming to depend on both clinical factors and the nature of the function.…”