Klinische Neurophysiologie 2012; 43 - P139
DOI: 10.1055/s-0032-1301689

Navigated transcranial magnetic brain stimulation: should the premotor cortex be stimulated for the mapping of the hand motor cortex?

P Spangenberg 1, S Lücke 2, M Meschede 2, A Harders 2
  • 1Neurochirurgische Klinik, Universitätsklinik Bochum, Bochum
  • 2Klinik für Neurochirurgie, Universitätsklinik Bochum, Bochum

Objective: Navigated magnetic brain stimulation (NBS) has become a valuable tool for mapping the motor cortex. Until now, the premotor cortex has not been regarded as a target for NBS mapping.

Methods: 5 human right handed adults were studied, 4 of which harbored a unilateral brain tumor. We used NBS for mapping of the precentral gyrus and premotor frontal cortex. During NBS, muscle activity was monitored online by electromyography. The motor threshold, amplitudes and latencies for the abductor digiti minimi (ADM) and abductor pollicis brevis (APB) muscles were determined. To visualize the cortical areas representing the hand muscles, stimulation sites that elicited motor evoked potentials were marked to the cortex surface.

Results: Mapping of the precentral gyrus showed the typical representation of the APB and ADM muscles in the hand knob of the precentral gyrus as described in Penfield’s homunculus. We found consistently in all hemispheres an additional hand motor area rostral to the hand knob of the precentral gyrus. This cortex area was mapped positive for both APB and ADM stimulation and had a similar size of the hand knob itself. This premotor hand area reacted to NBS by hand muscle activation as fast as the hand knob of the precentral gyrus. The motor threshold, amplitudes and latencies were similar in both cortical areas. This premotor hand motor cortex could also be detected in those hemispheres with a tumor residing in the central cortex.

Conclusion: The present study indicates that there are distinct cortical representations for hand motor executions rostral to the hand knob of the precentral gyrus. This premotor hand area seems to have direct corticospinal connections, has a similar size as the hand knob and can be detected by NBS in healthy hemispheres and also in cortices altered by a space-occupying lesions. Therefore NBS mapping of the premotor cortex should be performed gyrus on a routine basis.