Differential contribution of amygdala and hippocampus to cued and contextual fear conditioning.

TLDR

The study examined how the amygdala and hippocampus contribute to acquiring conditioned fear responses to a discrete cue versus contextual background stimuli in rats. Rats underwent lesions of either the amygdala or hippocampus, and their fear responses to tone–shock pairings and contextual cues were measured. Unoperated controls showed faster cue conditioning and greater resistance to extinction than contextual conditioning; amygdala lesions disrupted both cue and context fear conditioning, whereas hippocampal lesions impaired only contextual conditioning, indicating the amygdala mediates associative fear to both simple and complex stimuli while the hippocampus relays sensory information for complex, polymodal events.

Abstract

The contribution of the amygdala and hippocampus to the acquisition of conditioned fear responses to a cue (a tone paired with footshock) and to context (background stimuli continuously present in the apparatus in which tone-shock pairings occurred) was examined in rats. In unoperated controls, responses to the cue conditioned faster and were more resistant to extinction than were responses to contextual stimuli. Lesions of the amygdala interfered with the conditioning of fear responses to both the cue and the context, whereas lesions of the hippocampus interfered with conditioning to the context but not to the cue. The amygdala is thus involved in the conditioning of fear responses to simple, modality-specific conditioned stimuli as well as to complex, polymodal stimuli, whereas the hippocampus is only involved in fear conditioning situations involving complex, polymodal events. These findings suggest an associative role for the amygdala and a sensory relay role for the hippocampus in fear conditioning.