Behavioral activation of human hippocampal EEG: Relationship to recent memory

Behaviorally activated EEG was recorded from each hippocampus in 17 epilepsy surgery patients with unilateral (11 left, 6 right) mesial temporal lobe (MTL) seizure onset and correlated with preoperative material-specific memory test performances. Whole-band power (1-30 Hz) was recorded and subjected to spectral analysis under three conditions: (a) eyes closed resting, (b) eyes open with a verbal task, and (c) eyes open with a nonverbal task. Significantly less EEG desynchronization was observed in the epileptogenic hippocampus during the verbal activation condition but not during the eyes-open nonverbal task. Decreased EEG reactivity in the left hippocampus during verbal activation was correlated significantly with verbal memory test impairment among patients with left MTL seizure onset. However, similar relationships were not obtained between right seizure focus patients and performance on a visuospatial learning test. Results confirm the association of left MTL structures with verbal memory functions and emphasize the difficulty in demonstrating a consistent relationship between right MTL structures and visuospatial memory performance.