Academic journal article Cognitive, Affective and Behavioral Neuroscience

Value-Based Modulation of Memory Encoding Involves Strategic Engagement of Fronto-Temporal Semantic Processing Regions

Academic journal article Cognitive, Affective and Behavioral Neuroscience

Value-Based Modulation of Memory Encoding Involves Strategic Engagement of Fronto-Temporal Semantic Processing Regions

Article excerpt

Published online: 29 March 2014

© Psychonomic Society, Inc. 2014

Abstract A number of prior fMRI studies have focused on the ways in which the midbrain dopaminergic reward system coactivates with hippocampus to potentiate memory for valuable items. However, another means by which people could selectively remember more valuable to-be-remembered items is to be selective in their use of effective but effortful encoding strategies. To broadly examine the neural mechanisms of value on subsequent memory, we used fMRI to assess how differences in brain activity at encoding as a function of value relate to subsequent free recall for words. Each word was preceded by an arbitrarily assigned point value, and participants went through multiple study-test cycles with feedback on their point total at the end of each list, allowing for sculpting of cognitive strategies. We examined the correlation between value-related modulation of brain activity and participants' selectivity index, which measures how close participants were to their optimal point total, given the number of items recalled. Greater selectivity scores were associated with greater differences in the activation of semantic processing regions, including left inferior frontal gyrus and left posterior lateral temporal cortex, during the encoding of high-value words relative to low-value words. Although we also observed value-related modulation within midbrain and ventral striatal reward regions, our fronto-temporal findings suggest that strategic engagement of deep semantic processing may be an important mechanism for selectively encoding valuable items.

Keywords Value · Memory · Selective encoding · Reward · Metacognitive control · fMRI

It is generally true that some of what a person encounters is important to remember, whereas other things are less important. One critical operation is to selectively remember important information, often at the expense of less important information. For instance, when studying for an exam, some students might maximize efficiency, focusing exclusively on the most important material. Other students might not be as selective; even though they know that some items are more important than others, they may still try to remember as much as possible, a strategy that often leads to poorer results. In the present work, we used functional magnetic resonance imaging (fMRI) to better understand what people do differently, on both cognitive and neural levels, when remembering items deemed important.

In order to address these questions, we used a variant of the value-directed remembering (VDR) paradigm (Castel, 2008; Castel, Benjamin, Craik, & Watkins, 2002). The VDR paradigm involves having participants study a list of words paired with point values, with the participants' goal being to maximize the total score, which is the sum of the values associated with recalled words. A number of behavioral studies (e.g., Ariel & Castel, 2014; Castel et al., 2002; Castel, Farb, & Craik, 2007; Castel, Murayama, Friedman, McGillivray, & Link, 2013; Hanten et al., 2007; Loftus & Wickens, 1970; Soderstrom & McCabe, 2011; Watkins & Bloom, 1999) have shown that words that are arbitrarily determined to be valuable (via high point values) tend to be recalled better than words that are arbitrarily assigned lower values. However, prior studies with this paradigm have been limited in fully explaining the effect on a mechanistic level, with explanationsranging from differential forms of rehearsal, use of imagery, and strategic encoding and retrieval operations.

There is reason to believe that people make an explicit effort to prioritize encoding of high-value items in the VDR paradigm. Specifically, the degree to which people optimize their point score, as measured by the selectivity index (Castel et al., 2002), increases from earlier lists to later lists (Castel, 2008; Castel et al., 2011). The VDR paradigm is structured such that people learn multiple distinct word lists, with a free recall test after each list and immediate feedback on the number of points earned after each test. …

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