Poster E80, Monday, March 27, 2:30 – 4:30 pm, Pacific Concourse
Hippocampal theta oscillations differentiate recognition with and without correct source retrieval.
Kamin Kim1, Arne Ekstrom2, Nitin Tandon1; 1Department of Neurosurgery, University of Texas Medical School at Houston, 2Center for Neuroscience and Department of Psychology, University of California Davis
Past EEG findings have suggested that theta oscillations are associated with recognition and may reflect hippocampal-driven reinstatement of the episodic memory representation (Nyhus & Curran, 2010). However, specific evidence of hippocampal theta-driven reinstatement during recognition is lacking. Here, using intracranial EEG (iEEG), we investigated the electrophysiological characteristics of the hippocampal processing during recognition. Six patients participated in a spatiotemporal source memory task comprised of encoding and retrieval phases. During encoding, patients were presented with pictures of objects and asked to associate them with either a spatial or temporal context. During recognition/retrieval, they were again presented with the same objects and some new foil items and asked whether they had previously been shown the picture (familiar vs. unfamiliar, i.e., recognition) and also the context they associated with the item (i.e., source retrieval). iEEG data from the electrodes placed in the hippocampus were analyzed in a time window starting from 1000ms preceding the recognition cue onset till 2200ms after cue onset. Correct recognition trials were sorted according to whether the item was later identified with the correct source context or not. Time-frequency analysis was conducted using Hilbert transformation, and a permutation test was used to test the statistical significance of conditional differences. Significant increases in theta-band (3-8Hz) oscillations were associated with the items in which the source was later correctly identified. The present results suggest that in hippocampal theta oscillations may initiate distinct levels of cortical reinstatement for episodic memory with and without rich encoding of details.
Topic Area: LONG-TERM MEMORY: Episodic