Tests for emotionality in rats and mice: A review

Abstract This paper examines the concept of emotionality, particularly in relation to measures taken in ‘novel environment’ tests (e.g. the open field). Evidence of several different types is reviewed to assess the validity of the measures in relation to common assumptions underlying their use. In response to increased light and noise, open field defecation increases and ambulation decreases, and thus on this basis they may be termed emotional responses. In many cases defecation and ambulation in the open field showed a fairly low but significant inverse correlation. Nevertheless, a number of limitations to this relationship were found, depending on the species, strain, sex, sample size, and early experience; other, presumed, measures of emotionality in the open field showed little consistent relationship to defecation, but the evidence here was sparse. Studies measuring heart-rate responses provided insufficient evidence to relate open field defecation to this other response presumed to be under sympathetic nervous control. Ambulation showed little descriptive validity as a measure of exploration; owing to the occurrence of both immobility and escape behaviour as alternative forms of emotional behaviour, ambulation also provided an inadequate indication of emotional responses. Thus, conceptual frameworks which suggested that emotionality energized ambulation in a consistent manner were criticized. Open field defecation showed little relationship to supposed measures of emotionality taken in other types of tests (e.g. emergence tests, active avoidance learning); these findings clearly failed to support the use of emotionality as a consistent constitutional trait, with unitary drive properties. Two alternative methods were suggested, for testing: (a) responses to novel environments, and (b) emotional behaviour, without making assumptions that the measures represent unitary major motivational constructs.