Note on “Emotional Behavior in the Rat as a Function of Maternal Emotionality”
Ader and Belfer (1962) present findings on emotionality in rats, most of which accord with results of previous experiments utilizing larger groups. Their finding that at approximately 38 days of age offspring of "high-emotional" female rats were more emotional (less active) than those of "low-emotional'' mothers agrees with the demonstration by Hall (1951 for review) of the genetic basis of emotionality and the establishment of this in a long-term psychogenetic selection experiment by Broadhurst (1960 for review). Significant sex differences have also been found by others. However, Ader and Belfer also report a finding not in accord with previous results. They report that the difference between offspring of high- and low-emotional mothers disappears when offspring are retested at 136 days. At this age they found the activity of both groups to have declined. Candland and Campbell ( 1962) and Broadhursr ( 1960), in larger investigations, found that activity increases with age (over approximately the same range). The explanation for rhis difference might lie in the fact that only a single, short (1-min.) trial was given at each age of testing in the open field. Activity, parriculady in females, is influenced by factors in addition to emotionality, and a single trial is likely to give activity scores reflecting exploratory drive, oestrus cycle, etc. Activity scores are likely to be less contaminated, at least by sex variables, at 38 days than at 130 days. The offspring of Ader and Belfer's high-emotional mothers obtained consistently (but not significantly) higher defecation scores at both testlngs rhis disagreement of two supposedly related variables is itself evidence of the insuff~c~ency of an activity score based on a single short trial. If no account is taken of pre-trial defecation, defecation-score differences berween groups on a single trial are likely to be decreased. High- and lowemotional rats will, by definition, be differentially affected by pre-trial factors, reducing differences in the open field defecation scores. As single-trial open-field testing is becoming more frequent it is necessary to point out its probable limitations. Ader and Belfer's paper illustrates how such usage can produce results in conflict with other findings and which in addition can be taken to imply that their experiment casts doubt on the genetic basis of emotionality.