Amygdala activity at encoding corresponds with memory vividness and with memory for select episodic details

Abstract

It is well known that amygdala activity during encoding corresponds with subsequent memory for emotional information. It is less clear how amygdala activity relates to the subjective and objective qualities of a memory. In the present study, participants viewed emotional and neutral objects while undergoing a functional magnetic resonance imaging scan. Participants then took a memory test, identifying which verbal labels named a studied object and indicating the vividness of their memory for that object. They then retrieved episodic details associated with each object's presentation, selecting which object exemplar had been studied and indicating in which screen quadrant, study list, and with which encoding question the exemplar had been studied. Parametric analysis of the encoding data allowed examination of the processes that tracked with increasing memory vividness or with an increase in the diversity of episodic details remembered. Dissociable networks tracked these two increases, and amygdala activity corresponded with the former but not the latter. Subsequent-memory analyses revealed that amygdala activity corresponded with memory for exemplar type but not for other episodic features. These results emphasize that amygdala activity does not ensure accurate encoding of all types of episodic detail, yet it does support encoding of some item-specific details and leads to the retention of a memory that will feel subjectively vivid. The types of episodic details tied to amygdala engagement may be those that are most important for creating a subjectively vivid memory.

Figure 1

During encoding (top panel), participants viewed images presented in one of four quadrants, in one of four lists, and were asked one of four questions about each image. At retrieval (bottom panel), participants were shown the verbal labels corresponding to items that could have been studied and were asked to indicate whether that label referred to a studied object (“old”) or not (“new”). For labels judged to be old, participants then rated the vividness of their memory for the corresponding encoding episode, and selected the image exemplar, the question asked, the list in which the image was presented, and the quadrant in which the image was presented.

Figure 2

Activity in the right amygdala (Talairach coordinates: 34, −3, −12) showed a positive parametric relation to subjective memory vividness for the emotional items.

Figure 3

For emotional items, activity in the right amygdala corresponded with subsequent-memory only for the image exemplar but not for the other episodic details. For neutral items, amygdala activity did not show any correspondence to subsequent memory.