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Title:Shedding light on memory retrieval: reactivation of related information and its association with the hippocampus
Author(s):Walker, John A
Director of Research:Cohen, Neal J.
Doctoral Committee Chair(s):Cohen, Neal J.
Doctoral Committee Member(s):Fabiani, Monica; Gratton, Gabriele; Baillargeon, Renée; Voss, Joel L.
Department / Program:Psychology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):memory retrieval
cortical reactivation
hippocampal volume
episodic memory
optical imaging
relational memory
Abstract:Memory retrieval is a multifaceted process that involves the coordination of multiple areas of the brain including the cortical memory stores and the hippocampus, an area of the brain shown to be necessary for creating and using flexible bindings between items in memory. One phenomenon that has been shown to be associated with the retrieval of information from those cortical memory stores is reactivation. Reactivation is the finding that when participants retrieve information the areas that were originally active while processing that information come back online and are reactivated. In a previous study I and others had shown that associative or relational bindings between items can be used to reactivate the cortical processors of one another (Walker, Low, Cohen, Fabiani, & Gratton, 2014). The current experiments examined this reactivation of sensory cortices by looking at its association with the hippocampus, both in terms of relating the reactivation activity to structural measures of the hippocampus but also to possible methods by which the hippocampus and sensory cortex communicate. Additionally, this reactivation phenomenon was studied across the lifespan by demonstrating the earliest known time at which infants show this pattern of reactivation as well as showing aging effects in the possible communication between the hippocampus and sensory cortices and subsequent reactivation. The first experiment establishes an association between the hippocampus and reactivation of relationally bound stimuli in older adults aged 55-88 years old. In this study participants learned pairs of faces and scenes and were then shown one of the items (in this case the scene) in order to elicit reactivation of face processing regions. It was found that the magnitude of reactivation in these older adults is related to hippocampal volume. Entrainment of oscillatory activity, particularly in the theta band, has been suggested as a possible route through which the hippocampus communicates with sensory cortices. The second experiment combined data from two previous studies using the same face-scene pair study paradigm and examined whether oscillatory activity in the theta band was associated with memory ability and reactivation. Across all participants, the power of theta and oscillations (8-10 Hz) just above canonical theta (high theta) within the face processing regions was correlated with subsequent memory activity. When looking at the correlation between oscillatory power and reactivation, it was found that oscillatory power in that high theta band in the face processing region of interest was positively correlated with reactivation of that same region but only in young adults. Older adults showed no correlation between oscillatory power in the theta or high theta band and reactivation. These data indicate a possible route through which the hippocampus communicates with the cortex. The third study shows the earliest time in the lifespan to show reactivation effects in the cortex to stimuli that were presented only once. 9-month-old infants studied pairs of movie clips and sounds as well as sounds only and movie clips only. Much like the older and younger adults, presentation of a sound that was previously paired with a movie elicited reactivation of processors for the missing item (in this case reactivation of extrastriate cortex that was originally active for the movie clips) in these infants. The combination of these experiments show that this relational reactivation phenomenon takes place across the lifespan from 9 months old to 88 years old and is associated with the hippocampus. Oscillatory activity, which may represent the communication between the hippocampus and the sensory cortex, is associated with reactivation but this association is not present in old age.
Issue Date:2016-12-01
Rights Information:Copyright 2016 John Andrew Walker
Date Available in IDEALS:2017-03-01
Date Deposited:2016-12

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