The Effects of Isolation Rearing on Behavioural Inhibition in the Rat

Abstract

The possibility that isolation-rearing in the rat affects the development of inhibitory mechanisms was studied in a series of experiments. It was found that socially-isolated rats were (1) slower to learn both a lever-panel alternation, and a two-lever alternation schedule of reinforcement, (2) more persistent than controls in pressing a lever for food when a supply of identical “free food” was introduced into the operant chamber, but (3) similar to control rats in their response to preloading with food, a procedure which inhibited lever pressing to the same extent in the two groups. Finally, it was shown in a separate experiment that the effects of increased food deprivation on lever pressing in the presence of free food were qualitatively different from the effects of social isolation, and therefore the social/isolate difference cannot be interpreted as motivational. The possible contributions of neophobia to the difference are discussed. It is concluded that isolates may well suffer from a disinhibitory defect, but that there are probably other effects of isolation in addition.

Evidence for a relationship between cage stereotypies and behavioural disinhibition in laboratory rodents

“…an order of magnitude difference in extinction performance and rates of behavioural switching), together with the fact that environmental treatments which affect cage stereotypy [45] also impact brain development, extinction learning, and the disinhibition of responses [48,61], argue that the suite of intercorrelated signs reported here reflects a differential impact of the captive environment upon these animals.…”

“…[64]) of offspring. Fourth, treatments which enhance the development of cage stereotypies [45] also induce widespread changes in the brain, and a general disinhibition of behavioural responses in rodents [48,61]. Taken together, these studies argue for a role of dysfunctional behavioural organisation in cage stereotypy.…”

“…Since they stem from decreased behavioural inhibition, stereotypies caused by clinical or experimentally-induced basal ganglia dysfunction form part of a suite of changes in behaviour. These include enhanced rates of behavioural initiation [20,40]; 'impulsivity' [59]; impaired performance in tasks where responses must be suppressed or slowed [20,40,59]; the inappropriate repetition, or 'perseveration' of previous actions [20,39], which impairs performance in tasks such as extinction learning [23,31,48,67]; and a concurrent knowledge-action dissociation in such tasks, whereby human subjects know (and report) the correct response to make but are unable to suppress automatic repetition of a previous, incorrect response [67]. Thus along with stereotypies, isolationreared primates show poor abilities to suppress inap-propriate behaviour in extinction [7,27], while the stereotypy frequencies of human subjects with autism and schizophrenia correlate with their inappropriate repetition of responses in gambling or sequence-generation tasks [23,67].…”

Activity differences of individually and group-housed male and female rats

“…Only the latter effect was produced by isolation at any age and reversed by subsequent group housing. Because the longer emergence times of isolates may be due to "fear responses" rather than to a slower habituation to the emergence chamber as suggested previously (Brain & Benton, 1979;Morgan, Einon, & Nicholas, 1975), it is possible that isolation in rats affects the processes regulating "fear responses" in addition to those influencing exploratory behavior. The decline (through repeated testing, handling, etc.)…”

The effects of prolonged handling, scopolamine, and physostigmine on the activity of isolated and socially reared rats

“…Since the young rat normally engages in a very high level of social activity, it is not surprising that social and/or environmental impoverishment can have pronounced effects upon adult behavior. For example, isolated animals differ from communally raised or socially enriched animals in that isolated animals are commonly found to be more active (e.g ., Levitsky & Barnes, 1972;Sahakian, Robbins, Morgan, & Iversen, 1975;Valzelli, 1969), have larger adrenal glands (Geller, Yuwiler, & Zolman, 1965;Hatch, Wiberg, Baloza, & Grice, 1963), and generally do not perform as well in learning tasks (Bingham & Griffiths, 1952;Morgan, 1973;Morgan, Einon, & Nicholas, 1975).…”