Searching for motor functions in dysgenic cortex: a clinical transcranial magnetic stimulation and functional magnetic resonance imaging study.

OBJECT: Cortical motor organization/reorganization was studied in patients with malformation of cortical development (MCD) by applying two noninvasive motor mapping techniques: transcranial magnetic stimulation (TMS) and functional magnetic resonance (fMR) imaging.

METHODS

Eight patients (age range 6-22 years), all suffering from congenital hemiparesis of similar severity, were included. Underlying lesions were schizencephalies in four cases, nonschizencephalic polymicrogyria in one, and complex hemispheric malformations in three. All MCDs involved rolandic cortex of the hemisphere contralateral to the hemiparesis. Transcranial magnetic stimulation was used to search, in both hemispheres, for brain regions with corticospinal projections to the paretic hand, and cortical activation during simple repetitive movements of the paretic hand was monitored using fMR imaging. Transcranial magnetic stimulation identified abnormal ipsilateral corticospinal projections from the contralesional hemisphere to the paretic hand in six of eight patients, in all of whom fMR imaging activation of the contralesional hand area was demonstrated during paretic hand movement. In two patients with schizencephaly in this subgroup, additional activation was shown in the affected hemisphere, located in dysgenic cortex lining the schizencephalic clefts but without TMS evidence for corticospinal projections originating from these sites. Corticospinal projections to the paretic hand originating in the MCD were identified in the remaining two patients, one with (nonschizencephalic) polymicrogyria and one with a complex hemispheric malformation.

CONCLUSIONS

Malformations of cortical development can show various degrees of participation in motor functions, ranging from corticospinal ("primary") motor control, to putative participation as "nonprimary" motor areas, to absence of evidence for any functional participation. This information can be obtained, noninvasively, using a combination of TMS and fMR imaging.