Inhibitory fear memory engram in the mouse central lateral amygdala

Abstract

Engrams are cellular substrates of memory traces that have been identified in various brain areas, including the amygdala. Most engrams identified so far are formed by excitatory, glutamatergic neurons. However, little attention has been paid to defining GABAergic inhibitory engrams. Here, we report an inhibitory engram in the central lateral amygdala (CeL), a crucial area for Pavlovian fear conditioning. This engram is primarily composed of GABAergic somatostatin-expressing (SST+) and to a lesser extent of protein kinase C-{delta}-expressing [PKC-{delta}(+)] neurons. Fear memory is accompanied by a preferential enhancement of mIPSC frequency onto PKC-{delta}(+) neurons as well as a general increment of amplitude. Moreover, non-engram cells exhibit higher mIPSC frequency than engram cells. The inhibition of the CeL GABAergic engram disinhibits the activity of engram-targeted areas and increases selectively the encoded fear expression. Our data defines the behavioral function of an engram formed exclusively by GABAergic inhibitory neurons in the mammalian CNS.