Friday, January 05, 2007

Brain correlates of "flashbulb memory" of 9/11

The term "flashbulb memory" is used to describe the recall of shocking, consequential events such as hearing news of a presidential assassination. Sharot et al test the idea that the vivid detail of such memories results from the action of a unique neural mechanism. They study personal recollections of the terrorist attacks of September 11, 2001 (9/11) in New York City, combining behavioral and brain imaging techniques, with two goals: (i) to explore the neural basis of such memories and (ii) to clarify the characteristics of the emotional events that may give rise to them. Three years after the terrorist attacks, participants were asked to retrieve memories of 9/11, as well as memories of personally selected control events from 2001. At the time of the attacks, some participants were in Downtown Manhattan, close to the World Trade Center; others were in Midtown, a few miles away. The Downtown participants exhibited selective activation of the amygdala as they recalled events from 9/11, but not while they recalled control events. This was not the case for the Midtown participants. Moreover, only the Downtown participants reported emotionally enhanced recollective experiences while recalling events from 9/11, as compared with control events. These results suggest that close personal experience may be critical in engaging the neural mechanisms that underlie the emotional modulation of memory and thus in producing the vivid recollections to which the term flashbulb memory is often applied.

Figure: Blood oxygen level-dependent (BOLD) response and proximity to the WTC. (a) Coronal slice of the structurally defined left amygdala (outlined in red) that includes the peak active voxel. (b) Mean percentage signal change from the peak active voxel in the left amygdala, revealing a two-way interaction of trial type (9/11 vs. summer) x group (Downtown vs. Midtown). (c and d) ANCOVA contrasting activation during 9/11 trials vs. summer trials, with participants' distance from the WTC as a covariate, in voxels within the structurally defined amygdala (c) and posterior parahippocampal cortex (d). Warm colors indicate positive correlation, and cool colors indicate negative correlation. Participants who were closer to the WTC showed decreased activation in the posterior parahippocampal cortex and increased activation in the amygdala bilaterally during retrieval of 9/11 memories relative to summer memories.

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