The amygdala encodes specific sensory features of an aversive reinforcer

Abstract

Studies of reconsolidation, in which retrieved memories are altered and restored, offer an approach for exploring the associative structure of fear memory. We found that exposure to the unconditioned stimulus initiates an unconditioned stimulus-specific reconsolidation of learned fear in rats that depended on the amygdala. Thus, specific features of the unconditioned stimulus appear to be encoded in the amygdala as part of fear memories stored there.

Figure 1. Exposure to the unconditioned stimulus alone triggers memory reconsolidation

(a) Anisomycin (ANISO) infusions following an exposure to the footshock unconditioned stimulus alone disrupt the reconsolidation of auditory fear conditioning to both CSa and CSb [ANOVA: significant main effect of drug (F(_1,14)=21.70, p<.001), n=7 and n= 9 for ACSF and ANISO, respectively]. (b) Amnesic effects of anisomycin do not reverse within 4 weeks [ANOVA: significant main effect of drug F(_1,12)=36.06, p<.0001), n=7 and n= 7 for ACSF and ANISO, respectively]. (c) Short-term memory is not affected by anisomycin [n=6 ACSF; n=7 ANISO; No significant effects of drug (p=.7), conditioned stimulus (p=.5), or drug x conditioned stimulus (p=.5)]. Asterisks (*) indicate a significant difference between groups; error bars indicate standard error.

Figure 2. Reconsolidation is selective to the reactivated unconditioned stimulus

(a) Anisomycin infusions following either footshock (US_FOOT) or eyelidshock (US_EYE) selectively disrupt fear memory reconsolidation for the conditioned stimulus associated with the reactivated unconditioned stimulus [Drug x CS_TYPE x Reactivation-US_TYPE interaction (F(_1,24)=18.15, p<.001). Follow-up of the triple interaction with simple interaction effects indicated that anisomycin, following exposure to the US_FOOT (n=8 and n=6 for ANISO and ACSF, respectively) impairs freezing responding to the US_FOOT–paired conditioned stimulus (CS_FOOT), but does not affect freezing to the US_EYE–paired conditioned stimulus (CS_EYE) [ANOVA: significant main effects of drug (F(_1,12)=14.39, p<.01) and CS_TYPE (F(_1,12)=6.24, p<.05); and a significant CS_TYPE x drug interaction (F(_1,12)=8.60, p<.05)]. (b) Anisomycin infusions following an exposure to an US_EYE (n=8 and n=6 for ANISO and ACSF, respectively) impair freezing responding to the US_EYE–paired conditioned stimulus (CS_EYE), but do not affect freezing to the US_FOOT–paired conditioned stimulus (CS_FOOT) [ANOVA: significant main effects of drug (F(_1,12)=16.91, p<.01) and CS_TYPE (F(_1,12)=11.70, p<.01); and a significant CS_TYPE x drug interaction (F(_1,12)=9.57, p<.01)]. Asterisks (*) indicate a significant difference between groups; error bars indicate standard error.