The hippocampal formation participates in novel picture encoding: evidence from functional magnetic resonance imaging.

TLDR

Evidence supports the hippocampus and medial temporal lobe as crucial for long‑term memory encoding, yet few human imaging studies have shown signal changes during encoding or retrieval. The study used fMRI to examine normal subjects performing a novel picture encoding task. High‑speed echo‑planar imaging was employed to assess fMRI signal changes throughout the brain. During novel picture encoding, significant fMRI signal increases were observed bilaterally in the posterior hippocampal formation, parahippocampal gyrus, lingual, and fusiform gyri, marking the first fMRI evidence of robust hippocampal activity and indicating that encoding depends on interaction between ventral visual cortex and hippocampal structures.

Abstract

Considerable evidence exists to support the hypothesis that the hippocampus and related medial temporal lobe structures are crucial for the encoding and storage of information in long-term memory. Few human imaging studies, however, have successfully shown signal intensity changes in these areas during encoding or retrieval. Using functional magnetic resonance imaging (fMRI), we studied normal human subjects while they performed a novel picture encoding task. High-speed echo-planar imaging techniques evaluated fMRI signal changes throughout the brain. During the encoding of novel pictures, statistically significant increases in fMRI signal were observed bilaterally in the posterior hippocampal formation and parahippocampal gyrus and in the lingual and fusiform gyri. To our knowledge, this experiment is the first fMRI study to show robust signal changes in the human hippocampal region. It also provides evidence that the encoding of novel, complex pictures depends upon an interaction between ventral cortical regions, specialized for object vision, and the hippocampal formation and parahippocampal gyrus, specialized for long-term memory.