PATTERN COMPLETION AND PREDICTION ERROR IN HIPPOCAMPUS: A HI-RES FMRI STUDY

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The hippocampus is known to be critical for declarative memory, though the functional contributions of the subfields of human hippocampus remain underspecified. The anatomical organization of hippocampus¿¿which includes dentate gyrus, CA3, CA1, and subiculum¿¿suggests that CA3 and CA1 may differentially subserve memory-based prediction and the detection of prediction error (Lisman & Grace, 2005). In particular, CA3 is hypothesized to support the encoding of conjunctive memories that are subsequently ¿pattern completed¿ at retrieval, in essence making predictions about the present based on knowledge acquired in the past. CA3 is thought to pass these predictions to CA1, which is positioned to compare this output from memory with input from entorhinal cortex that transmits the present state of ¿sensory reality¿. To examine the functional contributions of CA3 and CA1 to pattern completion and the detection of prediction error, we used high-resolution fMRI to measure the functional response of MTL cortices¿¿perirhinal, parahippocampal, and entorhinal¿¿and the subfields of hippocampus proper. During intentional encoding (not scanned), subjects viewed face-house pairs. Subsequently, subjects were scanned at 3T (effective TR=2s, TE=41ms, 1.7 x 1.7 x 3 mm) while performing cued-recall followed by a yes/no probe decision. On each test trial, one element of a studied pair served as a retrieval cue, which was followed by a 7.5-s delay during which the subject attempted to retrieve the associate. Following the delay, a probe was presented¿¿either the correct associate (match) or an incorrect item (mismatch); subjects had 750 ms to make a yes/no response (this speeded response encouraged pattern completion during the delay period).