Abstract: The effects of ACTH 4-10 on rats' imitation learning was examined during the acquisition and extinction of a bar-press response for water reinforcement. Rats were exposed to either a bar-pressing conspecific (OB), an experimentally naive conspecific (ON), or an empty box (OE) during bar-press acquisition. In a factorial design, each rat was then exposed to one of the same three conditions during extinction. An 80 mcg dose of ACTH 4-10 was administered to half of the rats in each group prior to observation. Performance differences during acquisition were generally small, but significant performance differences during extinction were found. Social facilitation was indicated by the finding that rats extinguished in the presence of a conspecific exhibited significantly greater resistance to extinction than rats extinguished in the presence of an empty box. An imitation effect was also found. Rats that observed a bar-pressing conspecific during both acquisition and extinction (group OB-OB) showed significantly greater resistance top extinction than did groups OB-ON, CB-OE, or OE-OE. There were no significant effects of the hormone, however, relative to saline controls.

Abstract: (1) A conceptual model is developed in which spatial behaviour is density-dependent. The behaviour is classified as congregatory or migratory according to whether it results in movement towards or away from population concentrations. (2) Spatial behaviour is shown to result from both individual and population interactions. (3) The stability properties of the model are explored and it is shown how, under particular conditions, populations obeying the model have a population density regulating mechanism. (4) The similarity between the model and the potential energy curve of physics is noted, but it is emphasized that this is a behavioural not a physical model.