Stress During Adolescence Shapes Performance in Adulthood: Context-Dependent Effects on Foraging and Vigilance

Exposure to chronic stress during adolescence can shape behaviour, cognition and physiology in adulthood, but the consequences of these long-term changes remain unclear. Prior studies reporting altered performance following exposure to stress in adolescence have generally interpreted lasting changes as impairments. However, we have recently shown that exposure to chronic unpredictable stress during adolescence (from post-natal days 30-70) can enhance performance in a context-dependent manner during a foraging task. Increases in foraging performance, (previously measured by the number of rewards obtained), are often associated with trade-offs in other behaviours, such as vigilance. Here, we examined the effect of stress exposure in adolescence on adult foraging in male Sprague Dawley rats to determine (1) whether the increase in foraging performance exhibited by animals exposed to stress in adolescence is balanced by a decrease in vigilance, and (2) whether stress in adolescence alters time allocation between foraging and vigilance behaviours in low- and high-threat conditions. We found no evidence of a trade-off between foraging and vigilance; under low-threat conditions, rats exposed to stress in adolescence spent more time being vigilant compared with unstressed rats, suggesting that exposure to stress in adolescence enhances anticipation of threat in adulthood. Under high-threat conditions, adolescent-stressed and unstressed rats did not differ in foraging and vigilance behaviours. Given that we have previously found that rats exposed to stress in adolescence nearly double food intake under high-threat, and we now show that high-performing rats do not spend more time foraging, it appears that stress exposure in adolescence may enhance foraging efficiency (food consumed/time) under high-threat conditions rather than time allocation between foraging and competing behaviours. We also examined the relationship, at the level of the individual, between foraging performance and foraging and vigilance behaviours. We found that changes in individual foraging performance between low- and high-threat conditions were independent of behavioural changes (i.e. both highly and poorly performing rats were equally active and contacted a similar number of patches). This suggests that the ability to obtain many rewards under high-threat conditions may be related to efficiency, rather than the frequency of foraging and effort-related behaviours.