Exploration, distraction, and habituation in rats reared in isolation

Rats reared in isolation have been reported to show increased motor activity; the purpose of the present experiment was to establish whether they also show enhanced exploratory and orienting responses. Rats were reared in isolation or in social groups from Day 20 to Day 45. Subgroups of each rearing condition were either left undisturbed, received daily handling, or received daily handling and were given objects in their cages. From Day 45 all the rats were rehoused in groups of 6, and testing began at Day 73. In a 1st test exploration was measured by the number of contacts with objects placed in the home cage; and a 2nd test exploration was measured by responses to a holeboard; and in a 3rd test orienting was measured by the distraction produced by the presentation of a tone. When tested in novel situations, in contrast to their enhanced motor activity, isolates showed reduced exploration and orienting. This may have been due to a discrepancy between their adaptation level (established during rearing) and their current level of sensory input. In all the tests the isolates showed normal habituation, both within sessions and between sessions. An inability to habituate is not, as has been claimed, a general characteristic of isolates.