Nonhabituation processes affect stimulus specificity of response habituation in the crab Chasmagnathus granulatus

The escape response of the crab (Chasmagnathus granulatus) habituates to repeated electrical shock (SH) or to the presentation of a screen moving horizontally (H) or vertically (V) overhead. Stimulus specificity of the habituated response is shown 24 hr after training but not after either 90 or 45 min. This disruption at short intervals is explained by a transient effect that arises from training: SH training and H training attenuate and V training enhances reactivity. The attenuating effect of H training is reduced by naloxone when administered before but not after training. The results support the hypothesis that during the crab's training two types of processes takes place: a stimulus-specific, long-lasting habituation process that promotes between-sessions response habituation and a nonhabituation process that promotes nonstimulus-specific, less persistent changes of behavior that involve either response habituation or response sensitization. The effect of H training seems to be mediated by an opioid mechanism through secondary activation.