Poster D92, Monday, March 27, 8:00 – 10:00 am, Pacific Concourse
Organization of object representations across different medial temporal lobe structures
Anna Blumenthal1, Bobby Stojanoski1, Chris Martin1,2, Rhodri Cusack1, Stefan Köhler1,2,3; 1University of Western Ontario, 2University of Toronto, 3Rotman Research Institute
Functional neuroimaging research has established that perceptual representations of objects in the ventral visual stream are broadly organized by animacy and, for inanimate objects, by real-world size. While this organization has been well characterized in posterior occipito-temporal structures, it remains unclear whether it also captures the organization of object representations in the medial temporal lobe (MTL), specifically during memory decisions. In the current fMRI study we examined representational similarities in patterns of activity in the MTL during memory judgements for images of real-world objects, focusing on perirhinal cortex, parahippocampal cortex, and the hippocampus. Participants performed a continuous recognition-memory task on objects from 12 different categories, which were matched for accuracy across domains. Stimuli included multiple exemplars from each category, and participants were required to judge prior occurrence at the exemplar level. Multivariate representational similarity analyses revealed that, as in more posterior ventral visual pathway regions, animacy and real-world size shape the organization of object representations in the MTL. However, the precise organization of object representations differed across structures. Animacy was reflected in similarities of representations in parahippocampal and perirhinal cortex, but not in the hippocampus. Real-world size for inanimate objects, by contrast, was reflected in representational similarities in parahippocampal cortex and the hippocampus, but not in perirhinal cortex. These findings add to a growing body of evidence that highlights representational differences not only between the hippocampus and neocortical MTL structures, but also between perirhinal and parahippocampal cortex.
Topic Area: LONG-TERM MEMORY: Other