Natural predator and a human stimulus differently affect the behavior, cortisol and cerebral hemisphere activity of marmoset monkeys.

The behavior, cortisol concentration and cerebral hemisphere activity of twelve marmoset monkeys were determined during standardized predatory stress-related events. Each subject was submitted to three 5-min trials, randomly held at 2-week intervals: a human intruder, a taxidermized oncilla cat and a no-stimulus control trial. Stimuli were positioned outside the home-cage and the ensuing reaction recorded. Baseline tympanic membrane temperature (TMT) was subtracted from the post-trial measure to determine changes in blood flow induced by ipsilateral brain activity. Cortisol was assayed immediately after the post-trial TMT assessments. Both genders reacted fearfully/anxiously towards the stimuli - each condition inducing a distinct pattern. Cortisol increased only when females were confronted with the wildcat, with higher levels of alarm calls predicting lower cortisol release. When either stimulus was present, changes in TMT were detected, albeit only in the right ear. The specific directional shift in temperature was gender- and stimulus-dependent, requiring further investigation. The control trial did not alter any of the parameters. Marmosets thus exhibit flexible multileveled coping strategies towards different aversive events, yet in general these seem to be asymmetrically processed by the right cerebral hemisphere.