Alpha-Amylase increases predict a freezing-like response and cortical alpha oscillations
Individual differences in the reactivity of the sympathetic nervous system in response to stressful situations are thought to be an important predictor for psychological well-being and the focus of current scientific investigations. Here, we explored whether increased sympathetic nervous activity (SNA) was associated with reduced alpha power and with increased freezing-like behaviour (i.e., body sway) while watching threatening stimuli, reflecting enhanced attention. Salivary alpha-amylase (sAA) was used as a proxy for sympathetic nervous activity, which is elevated in stressful situations. A passive viewing task with affective pictures (unpleasant, neutral, pleasant) was carried out, and pre- and post- task sAA samples were taken. Oscillatory brain activity in the EEG and body sway were assessed simultaneously during the task. The results point to an increase in sAA being associated with reduced alpha power decrease to the unpleasant compared to the neutral pictures as well as increased freezing-like behaviour (i.e., reduction in body sway for unpleasant versus neutral pictures). It appears that an increase in SNA is linked to less attentional valence differentiation. Furthermore, our study corroborates findings from the animal literature in that the SNA increase is linked to a freezing-like response.