Reinstatement of conditioned fear and the hippocampus: an attentional-associative model.

An existing attentional-associative model of classical conditioning [Schmajuk N, Lam Y, Gray JA. Latent inhibition: a neural network approach. J Exp Psychol: Anim Behav Process 1996;22:321-49] is applied to the description of reinstatement in animals and humans. According to the model, inhibitory associations between the context (CX) and unconditioned stimulus (US) are formed during extinction, which help preserve the association between the conditioned stimulus (CS) and the US. However, summation and retardation tests fail to reveal these associations because (a) the CX is not attended or (b) a CX-CS configural stimulus formed during extinction is both poorly attended and weakly active during testing. When US presentations and testing occur in the same context, reinstatement is the consequence of a decreased CX inhibition and the increased attention to the CS, which activates the remaining CS-US association. When US presentations occur in the context of extinction but the CS is tested in a different context, reinstatement results from an increased attention to the CS and the combination of CS-CX and CX-US excitatory associations. The assumption that associations between CSs are impaired following neurotoxic hippocampal lesions or in amnesia, is sufficient to describe absence of reinstatement in those cases. However, additional assumptions might be needed to describe the effect of hippocampal lesions on other postextinction manipulations.