Phenotyping stereotypic behaviour: collective variables, range of variation and predictability

Stereotypy is the narrowing down of an animal's behavioural repertoire. Sta rting from normal behaviour there is a continuum between rich and free beha viour on the one hand, and dull and predictable stereotypies on the other. To study the continuum all that one needs are "knobs" (like drugs or stress ) that shift the behaviour from one end to the other, and a method for docu menting the behavioural shift. The degree of narrowing down of the animal's repertoire is measurable in terms of the number of "collective variables" available to the animal, the range of values each collective variable can t ake, and the predictability of sequences of movements. We substantiate this thesis by presenting examples taken from the normal and drug-induced behav iour of the rat. (C) 1999 Elsevier Science B.V. All rights reserved.