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

Stereotypy is the narrowing down of an animal’s behavioural repertoire. Starting from normal behaviour there is a continuum between rich and free behaviour on the one hand, and dull and Ž 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 documenting 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 take, and the predictability of sequences of movements. We substantiate this thesis by presenting examples taken from the normal and drug-induced behaviour of the rat. q 1999 Elsevier Science B.V. All rights reserved.