gms | German Medical Science

Objective: Although the majority of primary motor function of the brain is located in the precentral gyrus, studies showed the importance of motor areas located frontal and dorsal of the precentral gyrus. This phenomenon was also supposed to be even more present in patients with brain lesions when plastic reshaping impairs functional anatomy. Navigated transcranial magnetic stimulation (nTMS) is a modern technology which enables a precise location of those motor functions non-invasively. This study therefore examines the distribution of the primary motor areas throughout the cortex in a considerably large cohort of patients with brain lesions in or adjacent to the rolandic cortex.

Method: 100 patients with motor eloquent brain lesions were examined by nTMS motor mapping. Examined muscles were abductor policis brevis (APB), abductor digiti minimi (ADM), flexor carpi radialis (FCR) and the biceps muscle (BCS), for the lower limb tibialis anterior (TA) and gastrocnemius (GCN). The patients were divided into five groups according to lesion localization (prerolandic, rolandic, postcentral, temporodorsal, and parietal tumor). The distribution of motor areas among these groups and in general among all patients was on the one hand shown graphically by using SPM8 for normalization and fusion, on the other hand statistically determined by analyzing the latencies of muscular evoked potentials (MEP).

Results: The motor areas in the medial and superior frontal gyrus show longer latencies than those in the precentral gyrus in general. The mean value of the measured latencies in all patients for the ADM muscle was 23.55 ± 2.77 ms in the precentral gyrus, 23.94 ± 3.04 ms in the superior frontal and 24.00 ± 2.37 ms in the medial frontal gyrus (p=0.0055).

Conclusions: The study indicates that there are more primary motor areas frontal to the precentral gyrus as proved by short (monosynaptic) MEP.