Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Role of Medial Temporal Lobe in Item Recognition and Source Recollection of Emotional Stimuli

Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Role of Medial Temporal Lobe in Item Recognition and Source Recollection of Emotional Stimuli

Article excerpt

Recent neuroimaging results suggest that distinct regions within the medial temporal lobe (MTL) may differentially support the episodic encoding of item and relational information for nonemotional stimuli (for a review, see Davachi, 2006). The present study was designed to assess whether these findings generalize to emotional stimuli. Behaviorally, we found that emotion reduced item recognition accuracy but did not reliably affect relational memory. fMRI analyses revealed that neutral and emotional words elicited distinct activation patterns within MTL regions predictive of subsequent memory. Consistent with previous findings for neutral words, hippocampal activation predicted later relational memory, whereas activation in the perirhinal cortex predicted successful item recognition. However, for emotional words, activation in the amygdala, hippocampus, and posterior parahippocampal cortex predicted item recognition only. These data suggest that MTL regions differentially support encoding of neutral and emotional stimuli.

It has long been known that structures in the medial temporal lobe (MTL), including the hippocampus, perirhinal, entorhinal, and parahippocampal cortices, are instrumental for episodic memory formation (Scoville & Milner, 1957). Research in both animals and humans has focused on characterizing the contributions that different MTL regions make to episodic memory formation (Cansino, Maquet, Dolan, & Rugg, 2002; Davachi, Mitchell, & Wagner, 2003; Jackson & Schacter, 2004; Kirwan & Stark, 2004; Ranganath et al., 2004; Sperling et al., 2003; see Brown & Aggleton, 2001, for a review). Although there is evidence for distinct contributions of MTL subregions in episodic memory formation for neutral stimuli (Davachi et al., 2003; Kensinger & Schacter, 2006; Kirwan & Stark, 2004; Ranganath et al., 2004; Uncapher & Rugg, 2005; for a review, see Davachi, 2006), the precise contribution of these structures to episodic memory formation for emotional stimuli remains relatively unexplored. The goal of the present research is to directly compare the contribution of distinct MTL subregions to the formation of episodic memories for neutral and emotional stimuli.

Evidence from animal studies suggests that encoding of the individual items encountered within an episode may be supported by mechanisms distinct from those involved in the encoding of the relationship among those items (Brown & Aggleton, 2001; Cohen & Eichenbaum, 1993). One widely used method for determining in humans which episodic memories contain item and relational information is to objectively measure the ability to recover a specific detail engendered within the encoding episode, commonly referred to as source memory. Accurate recollection of a specific contextual detail associated with an item is indicative of relational memory, whereas recognition of the item itself without accurate recollection of contextual details indicates item memory only. Neuroimaging studies have shown that encoding-related activity in the hippocampus and posterior parahippocampal cortex correlates with later relational memory, whereas encoding activity in the perirhinal cortex correlates with later item recognition, irrespective of recollection of episodic details (Davachi et al., 2003; Kensinger & Schacter, 2006; Kirwan & Stark, 2004; Ranganath et al., 2004; Uncapher & Rugg, 2005). Furthermore, patients with lesions limited to the hippocampus have been reported to be selectively impaired on recognition judgments that depend on recollection of episodic details, leaving item recognition proportionally intact (Holdstock et al., 2002; Mayes, Holdstock, Isaac, Hunkin, & Roberts, 2002; Mayes et al., 2004; Yonelinas et al., 2002; but see Manns, Hopkins, Reed, Kitchener, & Squire, 2003).

Many behavioral studies have asked whether item and relational memory are enhanced for emotional stimuli, relative to neutral ones. …

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