Abstracts

In order to better comprehend the cortico-cortical networks involved in ictal motor manifestation (or phenomenology), it is essential to know cortico-cortical connections in the human motor system in vivo. The knowledge of neuronal in vivo connectivity in humans has been limited. Our understanding of thi subject comes from tracer injection techniques or in vivo studies in the nonhuman primate. Our aim is to investigate, in vivo, the cortico-cortical connection between lateral (lateral premotor, sensorimotor) and mesial (pre-SMA, SMA) motor cortices by means of a cortico-cortical evoked potential (CCEP) study. Seven patients with intractable partial epilepsy (age 1.6-46) underwent chronic subdural implantation in the lateral and mesial fronto-parietal regions for the presurgical evaluation. Single pulse electric stimuli (1Hz, alternating polarity, duration of 0.3 msec, at the intensity of subthreshold to clinical signs or afterdischarges) were delivered to the mesial (7 patients) and lateral motor (4) areas, and CCEPs were recorded by averaging electrocorticograms from the lateral and mesial motor areas, respectively, time-locked to the stimulus (bandpass 1-1000 Hz). The distribution of CCEPs were analyzed in relation to anatomical landmarks as well as functional regions. Short latency CCEPs were recognized both from the lateral (peak latency; mean 21.2 ms, range 9-47 ms) and mesial (mean 28.2 ms, range 11-59 ms) motor areas. Regression analysis revealed a consistent rostro-caudal correlation between the site of stimulation and the site of maximum CCEP on stimulation at both the lateral and mesial motor areas. Functionally, stimulation of the positive motor areas at the mesial and lateral motor cortices elicited CCEPs at the somatotopically homologous regions in the lateral (83%) and mesial (81%) motor cortices, respectively. In four subjects in whom stimuli were delivered to both the lateral and mesial cortices, reciprocality was observed between the two corresponding areas in the majority of connections (76-89%). The present study demonstrated, for the first time in vivo in humans, a cortical network connecting the rostral and caudal subdivisions each in the lateral and mesial motor cortices. Functionally, the somatotopically homologous regions were connected between lateral and mesial motor cortices.