Results from a signal detection analysis approach to the study of lasting effects of early life undernutrition on the behaviour of rats.

ABSTRACT

Rats were undernourished from birth to 45 days of age, first by underfeeding their mothers (50% of ad libitum diet) and then, from weaning at 25 days, by feeding the pups a restricted diet. They were fed ad libitum from 45 days till the start of behavioural testing at 29 weeks. Eleven well-fed control (C) and 10 previously undernourished (PU) male rats were trained to discriminate a brief decrement in light intensity. A response during this period was rewarded with food (a 'hit'); a response during an equivalent period in the absence of the signal (a 'false alarm') was penalised by delaying the onset of the next signal. Both groups of rats learned an easy discrimination equally well, but when the discrimination was made more difficult the PU rats required longer test sessions that C rats, made both more hits and more false alarms and had a higher responsivity index, indicating that the PU rats were more highly motivated than the C rats under this condition. Session duration increased on the more difficult discrimination; consequently time of day of testing changed somewhat and more for some rats than others. This may have been a confounding factor on the difficult discrimination and was specifically investigated in a follow-up experiment with the same rats. The results suggest that time may have been a conditioned stimulus and that the influence of this factor differed between C and PU rats.