Short-term memory in habituation and dishabituation of newborn chicks’ freezing response

Cognitive models of habituation and dishabituation postulate that the latter is attributable to the perturbation of the model of the repeated stimulation stored in short-term memory (STM) by the occurrence of a new stimulus, called dishabituator. However, although both behavioral phenomena depend on STM, previous studies in Aplysia have found that dishabituation seems to require further steps of development of the STM system to emerge. Here, we addressed whether this is a universal condition for the appearance of the 2 forms of learning, namely whether dishabituation must necessarily follow habituation. To this aim, we studied habituation and dishabituation of the freezing response to a sudden acoustic stimulation in newly hatched chicks (1 day old vs. 3 days old). The results showed that in chicks, dishabituation was fully present a few hours after hatching, a pattern of results indicating that, in this precocial avian species, habituation and dishabituation share the same developmental trajectory and the underlying STM mechanisms are simultaneously operative soon after birth.