Abstracts

Rationale: In addition to memory impairment, patients with mesial temporal lobe epilepsy (MTLE) often exhibit cognitive deficits, such as executive dysfunction, that suggest the functional involvement of structures beyond the temporal lobes. The neurophysiological basis of this involvement is still largely unknown but several lines of evidence suggest that interictal spikes originating from the epileptogenic zone may exert a remote effect on attention networks. Our aim was to investigate if the occurrence of interictal spikes in mesial temporal structures is associated with transient inhibition of cortical activity in remote areas belonging to the attention network. Methods: We studied 6 patients with MTLE (4 with left MTLE) who benefited from intracranial recording with subdural and depth electrodes. 100 spikes were used for each patient. Spectral power in the beta and low gamma band (20-50Hz), obtained by time-frequency decomposition with Morlet wavelets and used as a surrogate of cortical activity, was measure in 400ms interval following each spike and subsequently averaged over spikes. Results: A total of 645 electrode contacts were available at the time of recording. 20, 29 and 81 electrodes were located over the dorsal attention network (DAN; superior parietal lobule and frontal eye field, bilaterally), the ventral attention network (VAN; inferior parietal lobule and ventral frontal cortex, in the non-dominant hemisphere) and the fronto-parietal executive network (FPEN; inferior and superior parietal lobules and dorsal frontal and dorso-lateral prefrontal cortex, bilaterally), respectively. Both increases and decreases in beta/gamma band power were observed after spikes but decreases largely predominated in the areas of interest. Such transient decreases were observed in 9/20 contacts in the DAN, 11/29 contacts in the VAN and 28/81 contacts in the FPEN. The electrocorticographic correlate of these spectral perturbations consisted in low amplitude slow waves. Conclusions: Our results indicate that remote decrease in beta and gamma band power in cortical areas involved in attention and executive networks, suggestive of cortical inhibition in these regions, are not infrequent in patients with MTLE. Propagation of post-spike slow waves from the epileptogenic zone may be the electrophysiological substrate of attention and executive deficits in these patients.