The Neural and Cognitive Basis of Cumulative Lifetime Familiarity Assessment

Abstract

Perirhinal cortex (PrC) has been implicated as a brain region in the medial temporal lobes (MTL) that critically contributes to familiarity-based recognition memory, a process that allows for recognition to occur independently of contextual recollection. Informed by neurophysiological research in non-human primates, fMRI, as well as behavioural work in humans, the current thesis research tests the novel hypothesis that PrC cortex functioning also underlies the ability to assess cumulative lifetime familiarity with object concepts that are characterized by a lifetime of experiences. In Chapter 2, a patient (NB) with a left anterior temporal lobe (ATL) lesion that included PrC as well as an amnesic patient (HC) with a bilateral lesion to the hippocampus were tested on their ability to make lifetime familiarity judgements for object concepts (i.e., concrete nouns). Patient NB made abnormal familiarity ratings for objects concepts relative to matched controls, while patient HC produced ratings that did not differ from control participants. In Chapter 3, I tested healthy young adults on a frequency judgement task and lifetime familiarity task while they underwent fMRI. A region in the left PrC tracked both the perceived frequency of recent laboratory exposure as well as perceived lifetime familiarity. Finally, in Chapter 4, I tested whether indeed lifetime familiarity judgements are based on conceptual processing by making use of an associative priming paradigm. Associatively-related primes increased the perceived familiarity of object concepts while also reducing the latency of these judgements. Overall, the results from all three empirical chapters provides evidence that warrants an extension of PrC functioning to include the cumulative assessment of lifetime familiarity with object concepts