An important aspect of planning for epilepsy surgery is delineation of functional regions and epileptogenic regions. Using precisely-timed, computer-presented memory tasks (including maze navigation and recall of word lists), we analyzed the interictal electrical activity assocated with memory processing. Arrays of intracranial subdural electrodes captured the electrical responses generated in the brains of three epileptic patients who were learning to navigate computer-generated mazes.

S pectral analysis of the intracranial electroencephalogram (iEEG) revealed episodes of intense slow wave (theta) oscillations at numerous cortical loci. In and around limbic system structures, episodes of theta activity occurred more frequently and with greater intensity in mazes of greater complexity (p<0.01 in each patient, Mann-Whitney U test). Forty-eight of 171 electrodes showed a signifcant effect of complexity of task on theta activity (p<.01 at each electrode), and no electrode showed the reverse pattern, of greater theata acitivity in the less complex task.

These results demonstrate that theta oscillations, long implicated in spatial navigation in rodents, exhibit clear task-dependence during human spatial navigation. Implications of these findings for improved mapping of memory functions in evalutions of patients for resective surgery will be discussed.