J Epilepsy 1988;1:151-155 © 1988 Demos Publications Spectral Analysis of Human Hippocampal EEG: Behavioral Activation K Huh l K J. Meador l D. W. Loring, H. S. Taylor l D. W. King, B. B. Gallagher l IJ. R. Smith l and IH. F. Flanigin Hippocampal EEG was recorded from eight patients with intractable temporal lobe epilepsy who had depth electrodes implanted as part of their presurgical evaluation. The patients all had a mesial temporal seizure onset (5L. 3R) demon• strated by multiple ictal EEG recordings. A bipolar montage consisting of ascend• ing pairs of contacts on the hippocampal electrodes was employed. EEG was recorded during two states: eyes-closed resting and behavioral activation (Le., eyes-open, paired associate, verbal memory task). Hippocampal EEG power uni• formly decreased during behavioral activation. The percent decrease in spectral power was greater for the nonepileptogenic hippocampi than the epileptogenic hippocampi in six of eight patients. The results demonstrate response of the human hippocampal EEG to behavioral activation. Similar techniques may have utility in the preoperative evaluation for epilepsy surgery. Key Words: Hippo• campus- EEG-Epilepsy. The hippocampal EEG of animals is characterized by a predominant theta rhythm known as rhythmic slow activity (RSA) (1-3). Irregular slow activity and fast waves have also been noted from hippocampal recordings (4). These EEG patterns have been asso• ciated with a variety of behaviors in animals (e.g., at• tention, movement, learning). In contrast to the large body of literature concerning animal hippocampal EEG, very few studies exist examining behavioral ef• ects on the human hippocampal EEG. Lesse et a1. (5) investigated hippocampal recordings in four patients (three chronic schizophrenics and one patient with intractable pain). In their study, the resting EEG ex• hibited a mixture of slow and fast frequencies that From the Departments of Neurology and ISurgery (Sec• tion of Neurosurgery), Medical College of Georgia, Augus• ta, GA, U.S.A. Address correspondence and reprint requests to Dr. K J. Meador at Section of Behavioral Neurology, Department of Neurology, Medical College of Georgia, Augusta, GA 30912, U.S.A. were irregular and appeared desynchronized. They reported distinct, reproducible, high-voltage bursts of 14-17-Hz waves from the hippocampus during recollection of emotionally significant memories. and with olfactory stimulation. However, no character• istic EEG changes were noted during other tests of recent or remote memory, other modalities of peri• pheral stimulation, or other types of cognitive '!ctiva• tion (e.g., arithmetic problems). Reporting on hippo• campal EEG in 12 epileptic patients (8 with temporal lobe seizure onset), Pagni and Marossero (6) found no .synchronizing theta activity, no characteristic spontaneous hippocampal EEG, and very poor reac• tivity to exteroceptive and psychic stimuli. Employing spectral analysis of hippocampal EEG in 28 epileptic and 2 schizophrenic patients, Brazier (7) reported a high content of delta and theta activity in the resting state. During sleep, the slow activity increased, but coherence in ipsilateral limbic structures decreased. In 16 psychomotor epileptics, Halgren et a1. (8,9) found a single patient with visually obvious resting theta activity that desynchronized during tasks of at- J EPILEPSY, VOL 1, NO.3, 1988 151