Abstracts

Rationale: It has been reported that high frequency electrical stimulation of a certain cortical area in the frontal lobe elicited arrest of voluntary movements in patients with intractable partial epilepsy. This cortical area was named the negative motor area (NMA) because of the characteristic phenomena called the negative motor response (NMR). The neurophysiological mechanisms governing NMR remain unknown. The purpose of this study was to investigate precise definition of the connectivity associated with NMA in comparison with that of the primary motor area and elucidate the functional meaning of the negative motor phenomena. Methods: Four patients who underwent chronic intracranial electrode placement for the presurgical evaluation of medically intractable partial epilepsy were studied. Alternating 1 Hz electrical stimuli were delivered in a bipolar fashion to primary motor area (MI) and primary NMA (PNMA). CCEPs were recorded by averaging electrocorticograms from the subdural and depth electrodes.Results: In MI stimulation, CCEP responses were obtained from the precentral gyrus, the postcentral gyrus with larger amplitude. CCEPs were also observed in PM, posterior parietal cortex (PPC) and the temporo-parietal junction (TP junction). Electrical stimulation of PNMA elicited CCEPs in prefrontal cortex (PFC), PM, the precentral gyrus, the postcentral gyrus, PPC and TP junction with broader distribution in frontal or parietal association cortex than MI stimulation. CCEP responses were also obtained in the frontoparietal subcortical region with the depth electrodes.Conclusions: Compared to stimulation of MI, PNMA stimulation revealed broader distribution of CCEP responses in the frontal or parietal association cortex indicating the importance of the fronto-parietal network associated with higher level of motor control. We concluded that these connections are associated with functional organization of movement and the negative motor phenomenon results from impairment of the organization and integration of movements.