Context shift and protein synthesis inhibition disrupt long-term habituation after spaced, but not massed, training in the crab Chasmagnathus

An opaque screen moving overhead elicits an escape response in the crab Cha smagnathus that after a few presentations habituates for a long period (lon g-term habituation, LTH). Previous results suggested that spaced (15 trials separated by 171 s) and massed training (300 trials without rest interval) were correlated with two different memory components of LTH. The present e xperiments were aimed at further studying the mechanisms subserving these c omponents. Results indicate that LTH. acquired by spaced but not by massed training is blocked either by a training-to-testing context shift or by cyc loheximide (15-25 mu g) pre- or posttraining injection and that LTH after s paced training persists for longer time (5 days) than after massed training (2 days). A model based on these results that distinguishes two LTH-memory components is proposed: a (context-signal) LTH yielded by spaced training, dependent of context, sensitive to cycloheximide (CYX), and long lasting; and a (signal) LTH yielded by massed training, dependent only on the signal invariance, insensitive to CYX, and Shorter lasting. (C) 1999 Academic Pre ss.