The amygdala and prioritization of declarative memories

Abstract

The present review highlights results from recent studies that delivered brief electrical stimulation to the basolateral complex of the amygdala in rats to reveal its capacity to prioritize declarative memories on a moment-to-moment basis even after the moment has passed. The results indicate that this memory enhancement depends on the hippocampus and elicits intrahippocampal gamma synchrony that possibly corresponds with sharpened hippocampal spike-timing dependent plasticity. These recent findings are discussed in relation to past studies of emotional memory in rodents and humans.

Keywords: amygdala; consolidation; emotion; memory; stimulation.

Figures

Figure 1

Memory performance on a novel object recognition memory task on a test of half the objects given immediately after the initial study session and a test for the other half given one day later. Results are shown for objects for which the offset of initial exploration during the study phase was immediately followed by stimulation of the BLA and for objects for which initial exploration was not followed by stimulation. Performance is plotted as a discrimination index that represents the ratio of time spent exploring novel and repeated objects, which is used to infer memory for the repeated objects. A discrimination index of 0.50 (dashed line) represents chance performance, and a discrimination index of 0.65 (a 2:1 ratio of novel:repeated object exploration) is often considered to be near the upper limit of memory performance for the repeated objects on the task. Error bars show SEM. Data are combined from Bass et al., 2012 (n=9), Bass et al., 2014 (n=9; saline condition), and Bass and Manns, 2015 (n=7). Performance on the immediate test is nearly the same for both stimulation conditions. On the one-day test, memory performance is markedly higher for objects for which the initial exploration during the study phase was followed by stimulation of the BLA (t(24) = 3.59; p = 0.001; 95% confidence interval of the difference = 0.031 to 0.115).