Abstracts

Rationale: High density electroencephalography (HDEEG) recorded from scalp has demonstrated important clinical applications, particularly for pre-surgical planning in patients with medically refractory epilepsy. In addition to identifying a seizure onset zone, presurgical evaluation is necessary for localizing functional and dysfunctional regions to better understand the potential risk of surgery. Noninvasive preoperative techniques to assess memory risks are inadequate. Due to HDEEG’s high temporal and spatial resolution, it may be a useful tool for noninvasive measurement of memory function. In the current study, we attempted to assess hippocampal function by recording HDEEG in healthy adults during an auditory oddball task, which have previously recorded hippocampal activity in stereotactic EEG recordings. The task elicits a positive waveform on scalp approximately 300 ms after the onset of rare stimuli (P300).

Methods: HDEEG recordings were collected from eight healthy adult subjects during an auditory oddball task. Subjects were presented with two tones (1000 Hz and 2000 Hz) in pseudorandom order in a 4:1 ratio. They were asked to count the number of 2000 Hz target tones presented. Either 300 or 600 total trials were presented to subjects. Data were preprocessed to remove artifacts. Using an average reference, grand average scalp data at Cz was assessed to determine the peak latency of the P300 waveform. The latency was then used to compare targets and standards using a region of interest analysis examining left and right hippocampi. A 2x2 repeated measures ANOVA compared the current density of targets vs. standards between the left and right hippocampi.

Results: The ANOVA demonstrated that at the peak latency of the P300, the target stimuli had greater current density compared to standards (p  < 0.05). There was no difference observed between left and right hippocampi (see Figure of grand average P300 waveforms).