41. Slow negative erp recorded in human hippocampi during a simple sensorimotor task occurs independently of motor execution

Abstract

A hippocampal-prominent slow negativity with a peak latency at around 450 ms is consistently observed as a correlate of hippocampal activity during various cognitive tasks. Some intracranial EEG studies demonstrated that hippocampal evoked activity is related to movement execution as well as stimulus evaluation and associated memory processes. The aim of the present study was to investigate the temporal relationship between the latency of the hippocampal slow negative potential and motor responses. We analyzed ERPs recorded with 22 depth electrodes implanted into the hippocampi of 11 epileptic patients. Subjects were instructed to press a button after the presentation of a tone. In each subject, the artifact-free EEG segments were (1) sorted according to the respective RT from the fastest to the slowest responses, (2) divided into five subgroups and averaged separately (sorted averages). Finally, the ERP latency and relative latency, obtained from all five sorted averages, were correlated with the median RT for each subgroup. All investigated hippocampi generated a prominent negative ERP peaking at approximately 420 ms. In 16 from 22 cases we found that the ERP latency did not correlate with the reaction time; in different subjects, this potential could either precede or follow the motor response. Our results indicate that the hippocampal negative ERP occurs independently of motor execution. We suggest that hippocampal slow negativity, recorded in a simple sensorimotor task, is related to the evaluation of stimulus meaning within the context of situation.