Multimodal approaches towards a better understanding of feelings of familiarity

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Familiarity is a fundamental memory process that alerts us that we have experienced something before. Researchers have used one of three prevailing methods used to measure familiarity. This research has reported small and sometimes significant familiarity deficits in healthy older adults, compared to younger adults. Amnestic mild cognitive impairment (aMCI) is of particular interest in the study of familiarity because the earliest pathology occurs in the perirhinal cortex (i.e., Braak s transentorhinal' cortex) and entorhinal cortex, two regions that show cell loss and cortical thinning in aMCI. Most neuroimaging research finds perirhinal activation associated with familiarity, and research with patients with focal lesions finds familiarity deficits damage to the perirhinal cortex. It would thus be logical to hypothesize that familiarity is impaired in aMCI, compared to healthy older adults, but the evidence is evenly mixed: when conditions support high levels of recollection, familiarity is spared in aMCI, but when conditions support low levels of recollection, familiarity is impaired in aMCI, compared to their healthy counterparts. I suggest that higher contributions of recollection overshadow familiarity deficits in aMCI, and potentially in healthy aging, and that we need to utilize new methods to measure familiarity in recollection-free contexts.******I propose to supervise HQP in the study of familiarity in healthy younger and older adults, adults with lesioned perirhinal cortex, and older adults with neurodegenerated perirhinal cortex due to aMCI. The first five Experiments will examine familiarity from a behavioural perspective. Experiments 1, 2, and 5 will focus on encoding manipulations of familiarity, by varying the frequency with which stimuli are incidentally encoded prior to frequency ratings. Experiments 3, 4, and 5 will focus on retrieval manipulations familiarity, using a response deadline procedure, and a recognition-without-identification procedure. Biomarkers of familiarity in the most robust encoding and retrieval manipulations will then be further examined in Experiments 6, 7, and 8, using event-related potentials, pupil dilation, and skin conductance responses. I predict that compared to healthy young adults, healthy older adults and especially people with damaged perirhinal cortex due to aMCI or lesions will demonstrate familiarity deficits and compromised early old/new event-related potential effects, pupil dilation, and skin conductance latency.******This proposal heeds calls to challenge the fundamental notion that recollection and familiarity are stochastically independent, and provides a multimodal approach that will reshape the field's understanding of feelings of familiarity. Understanding both spared and impaired feelings of familiarity will provide us with a better understanding of the range of human mnemonic experience.