A cognitive neuroscience study of stress and motivation

Humans regularly encounter threatening stimuli, whether the mundane brooding expressions displayed by angry interlocutors or the extraordinary survival risks posed by extreme conditions in spaceflight. Neural system mobilization to stress has been implicated in anxiety and affective disorders, cancer and cardiac disorders, and, in space, problems from microgravity, radiation, and sleep deprivation. The present study considered the complex interaction of neural systems in two cases of performance under stress: (1) viewing of angry faces to determine the neural systems activated by survival-threatening stimuli, and (2) engaging in a frustration-provoking task; and examined how stress reactions are recruited as a function of the individual's perception of the stressor as a risk to survival.; In Experiment 1, faces were presented to normal participants and brain activation was measured with functional magnetic resonance imaging. Assessment over four runs determined whether responses to angry faces showed adaptation relative to neutral faces. In contrast to previous studies that reported habituation to fearful faces in amygdala and prefrontal cortex, the angry faces evoked sensitization in hippocampus, caudate, putamen, thalamus, fronto-orbital cortex, and insula. Off-line measures indicated that participants considered the angry and fearful faces to be non-rewarding and uniformly rated them as unpleasant, stress- and anxiety-inducing and threatening relative to happy and neutral faces. Angry faces were perceived to be significantly more direct threats than fearful faces. They recruited brain regions known to be activated during pain perception and elicited a perceptual equivalent of cutaneous allodynia.; In Experiment 2, normal participants engaged in space-docking simulations while their performance and heart and breathing rates were monitored. Penalty/reward context was varied across blocks of trials in high and low stress sessions. A training task set the frustration-provoking level of time pressure for each participant. Participants were subsequently queried as to their perception of the penalty/reward contexts. Participants who reported being motivated by monetary compensation, a proxy for survival risk, performed best overall and with least increase in heart rate in the neutral, followed by the context rewarding context, and worst in the penalizing context and performed better with lower heart rate increase in the low stress than in the high stress session.; In sum, these two experiments identified effects of survival stress on human physiology and performance by identifying the brain regions activated and performance differences resulting from survival stress under varying motivational contexts.