Amygdala activity is associated with the successful encoding of item, but not source, information for positive and negative stimuli

This study investigated whether the amygdala plays a differential role in encoding positive versus negative emotional stimuli and whether its activity supports memory for the item itself versus the contextual details (source) of that item. The researchers aimed to determine if the medial temporal lobe (MTL) dissociations observed for neutral information—where the hippocampus supports context and the entorhinal cortex supports item familiarity—also apply to emotional information.

Participants underwent functional magnetic resonance imaging (fMRI) while viewing positive, negative, and neutral words and pictures. During encoding, participants performed one of two tasks: judging whether the item was animate or whether it was commonly encountered. After a delay, participants completed a surprise recognition test to determine if they could identify the item and the specific task (source) associated with it. The researchers used event-related fMRI analysis to identify brain regions where activity during encoding predicted subsequent memory performance.

The study found that amygdala activity was equally related to the successful encoding of positive and negative items, suggesting it is not biased toward negative valence. However, while amygdala activity predicted memory for the item itself, it did not predict memory for the task performed (source). In contrast, activity in the hippocampus was specifically associated with successful source memory, while the entorhinal cortex was associated with item memory, regardless of the emotional valence of the stimuli. This indicates that the amygdala's role in memory enhancement is selective; it boosts memory for the emotional item but does not necessarily facilitate the binding of peripheral contextual details.

These results clarify the limits of the amygdala's influence on memory. While the amygdala is critical for the "emotional memory boost," it does not ensure that all aspects of an experience are encoded with equal fidelity. By showing that the amygdala's role is restricted to item-level memory, the study helps explain why emotional memories can feel vivid yet sometimes lack accurate contextual detail. It also confirms that the functional architecture of the MTL, which separates item and context processing, remains consistent even when emotional arousal is involved.