Using fMR-adaptation to track complex object representations in perirhinal cortex

Abstract

Brain regions in medial temporal lobe have seen a shift in emphasis in their role in long-term declarative memory to an appreciation of their role in cognitive domains beyond declarative memory, such as implicit memory, working memory, and perception. Recent theoretical accounts emphasize the function of perirhinal cortex in terms of its role in the ventral visual stream. Here, we used functional magnetic resonance adaptation (fMRa) to show that brain structures in the visual processing stream can bind item features prior to the involvement of hippocampal binding mechanisms. Evidence for perceptual binding was assessed by comparing BOLD (blood-oxygen-level-dependent) responses between fused objects and variants of the same object as different, non-fused forms (e.g., physically separate objects). Adaptation of the neural response to fused, but not non-fused, objects was in left fusiform cortex and left perirhinal cortex, indicating the involvement of these regions in the perceptual binding of item representations.

Keywords:

• fMR-adaptation
• Item representations
• Perceptual binding
• Perirhinal cortex
• Unitization

Acknowledgments

This research was funded by R03 MH082086 and NIMH R01 MH062500.

Notes

¹Hereafter, where violations of sphericity occurred, Greenhouse-Geisser corrected p-values are reported; for clarity, unadjusted df are reported.

²One−tailed thresholds were used for the remaining contrasts given that fMRI adaptation lends itself to clearly directional predictions.