Feeding neophobia: a possible explanation for the differential maze performance of rats reared in enriched or isolated environments.

This study undertook a detailed examination of the now-classical isolate maze deficit. Three male littermates from each of 19 litters were exposed to early and lengthy environmental enrichment, isolation, or isolation plus frequent handling. At 120 days of age subjects were tested on the open field, on an emergence task, and in a complex maze. Subjects were allowed to enter and leave the maze goal box at will. Only after eating for 30 seconds were they captured and replaced in the start box for the next trial. In the open field and emergence tasks the enriched and isolate rats both showed symptoms of much greater timidity than the experimenter-adapted handled rats. In the maze, enriched rats increased goal box entries over days, handled and non-handled isolates did not. By day three, handled and non-handled isolate goal entries were significantly lower than for enriched rats. This finding suggests an intellectual deficit in isolate maze learning. However, error analysis revealed that even on day one, all groups made errors at a rate far below random. The pattern of errors implied that subjects were often actively avoiding the goal, with isolates turning aside before entering the goal significantly more often than enriched rats. These findings suggest that the isolate maze deficit is due to a form of feeding neophobia. More generally, it would appear that these behavioral differences reflect early learning, with handled rats less afraid of humans and enriched rats better adapted to eating in novel surroundings.