Individual differences in amygdala activity predict response speed during working memory

Abstract

The human amygdala has classically been viewed as a brain structure primarily related to emotions and dissociated from higher cognition. We report here findings suggesting that the human amygdala also has a role in supporting working memory (WM), a canonical higher cognitive function. In a first functional magnetic resonance imaging (fMRI) study (n = 53), individual differences in amygdala activity predicted behavioral performance in a 3-back WM task. Specifically, higher event-related amygdala amplitude predicted faster response time (RT; r = -0.64), with no loss of accuracy. This relationship was not contingent on mood state, task content, or personality variables. In a second fMRI study (n = 21), we replicated the key finding (r = -0.47) and further showed that the correlation between the amygdala and faster RT was specific to a high working memory load condition (3-back) compared with a low working memory load condition (1-back). These results support models of amygdala function that can account for its involvement not only in emotion but also higher cognition.

Figure 1.

Schematic diagram of an n-back task. Stimuli are displayed sequentially on a screen and subjects are instructed to decide through a button press whether the current stimulus is equal or different from the stimulus displayed n trials back. In this example, n = 3.

Figure 2.

Statistical map of Pearson correlations between brain activity and task response time in experiment 1 (threshold, p < 0.05, cluster-level corrected) showing clusters of negative correlations in the left and right amygdala on coronal (a), transverse (b), and sagittal (c) views (peak voxel correlation: x = −20, y = −6, z = −21).

Figure 3.

Scatterplot of the peak voxel correlation between the left amygdala and response time in experiment 1 (after controlling for outliers): x = −20, y = −6, z = −21; r = −0.60; p = 0.000001.

Figure 4.

Correlations between anatomical ROI of the left amygdala and task response time by WM load condition for experiment 2 (after controlling for outliers). Correlations are significant for the 3-back condition (r = −0.47; p < 0.05) and for the 1-back condition (r = 0.49; p < 0.05).

Figure 5.

Averaged time course of the left amygdala ROI by WM load condition and performance group for experiment 2 after baseline correction. The effect of cognitive load is specific to the H-P group (see Results).

Figure 6.

The x-axis represents a difference in amygdala activity (3-back minus 1-back) using an anatomical ROI of the left amygdala, and the y-axis represents median response time for experiment 2 (after controlling for outliers). Correlations are significant for the 3-back condition (r = −0.73; p < 0.001) and for the 1-back condition (r = −0.63; p < 0.005).

Figure 7.

Averaged time course of the right amygdala ROI by WM load condition and performance group for experiment 2. The main effect of cognitive load is significant independently of performance group (see Results).