Adaptation to cognitive context and item information in the medial temporal lobes - PubMed (original) (raw)

Adaptation to cognitive context and item information in the medial temporal lobes

Rachel A Diana et al. Neuropsychologia. 2012 Nov.

Abstract

The medial temporal lobes (MTL) play an essential role in episodic memory, and accumulating evidence indicates that two MTL subregions--the perirhinal (PRc) and parahippocampal (PHc) cortices--might have different functions. According to the binding of item and context theory (Diana, Yonelinas, & Ranganath, 2007; Eichenbaum, Yonelinas, & Ranganath, 2007), PRc is involved in processing item information, the target of memory encoding, whereas PHc is involved in processing context information, peripheral information that identifies the circumstances of the episode. Here, we used functional magnetic resonance imaging (fMRI) adaptation to test the roles of different MTL subregions in the processing of item and context information. Participants were scanned while viewing a series of objects. Each object was presented with a unique semantic encoding question that elicited a salient cognitive context. The object picture, the encoding question, both, or neither were immediately repeated. We found that PRc activity was sensitive to repetition of the object but not the encoding question whereas PHc activity was sensitive to repetition of the encoding question but not the object. These data are consistent with the idea that the PRc and PHc are differentially involved in the representation of item and context information and additionally suggest that the role of the PHc extends to nonspatial, cognitive context information.

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Figures

Figure 1. Sample trial layout for RC and RI conditions

RC indicates repeated presentation of a semantic encoding question, as seen in the frames on the left. RI indicates repeated presentation of an object picture, as seen in the frames on the right. (Actual object stimuli were presented in color.)

Figure 2. fMRI adaptation effects and estimated time courses in medial temporal lobe areas

Voxels showing overall adaptation effects (reduced activation in the RA condition as compared to the NR condition) are overlaid in blue on the brain images. FIR set analysis beta values were extracted from the peak cluster within each medial temporal lobe anatomical region, averaged across hemispheres, and are plotted as time courses for the hippocampus, PRc, and PHc in the center. Interpolation between data points in the time course plots was based on the “smoothed line” algorithm implemented in Microsoft Excel (based on fitting a 4 point Bezier curve to the observed data).

Figure 3. PRc and PHc show qualitatively different patterns of adaptation during item vs. context repetition

Bar graphs illustrate mean beta values in PHc and PRc for the RI and RC conditions averaged across peak 2 TRs for each brain region.

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Adaptation to cognitive context and item information in the medial temporal lobes - PubMed (original) (raw)