Representational Approach to Hippocampal Functions : a fMRI Study

Traditional neuropsychological models associate the medial temporal lobe (MTL) with episodic memory. Further, the hippocampus would be responsible for recollection, or the rich and contextualised retrieval of a memory; whereas the perirhinal cortex (PRC) would process familiarity, or the feeling that a stimulus has been encountered before, without remembering where or when it happened. However, there is growing evidence questioning this view, and supporting an alternative proposal. The representational view of the MTL proposes that such regions would not be organised according to cognitive processes, but rather according to the representations (or the mnemonic content, represented by a pattern of neuronal spikes. A 2018-fMRI study demonstrated that the engagement of the hippocampus in recollection depends on the presence of a spatial scene in the memory that is retrieved, and not on the reconstructive nature of the retrieval. However, this demonstration is incomplete, as the only process that was investigated is recollection. The current project aims to extend such results to memory processes such as familiarity, and even to non-mnemonic processes such as visual discrimination. A fMRI study will thus be conducted, where 30 healthy participants will first perform a visual-discrimination task on scenes and objects, before taking a recognition task, in which images will either be presented in full or in the form of circular cues only. Multivariate-Pattern Analyses (MVPA) will complete traditional fMRI analyses, in order to determine whether activity in the MTL can be categorised on the basis of representations through a machine-learning classifier.

Inclusion criteria

• Affiliation to French Healthcare system
• No contraindication to MRI examination
• Age between 18 and 35 years-old
• Visual acuity permitting normal perception of stimuli or corrected sight

Exclusion criteria

• Existence of a pathology incompatible with the protocol : Heart, respiratory, haematological, caner, neurological disorder...
• Brain-modulating medical treatment
• Alcohol intake before examination
• Uncorrected visual disorder
• Cognitive deficit (criterion MMSE < 27)
• People protected by articles L1121-5 to L1121-8 of the CSP (pregnant women, under-18 subjects, people under judiciary or administrative surveillance)