Dynamics of Induced Cortical Electrical Activity during the Pauses between Target and Trigger Stimuli on Formation of a Set to an Emotionally Negative Facial Expression

Abstract

Studies in healthy adults (n = 70) using a cognitive set model addressed the effects of increased loading on working memory, imposed by lengthening the pause between the target (facial image) and trigger stimuli, on recognition of a facial emotional expression. Increases in the interstimulus interval from 1 to 8 sec led to increases in set plasticity and decreases in the number of contrast illusions on recognition of facial expressions, along with reductions in trigger stimulus reaction times. Analysis of EEG dynamics in the alpha and theta ranges during individual segments of the interstimulus pause led to a hypothesis for the neural mechanisms of these changes in cognitive activity. The initial hypothesis was: repetition of stimuli with a particular pause leads to learning, which forms an internal representation of the time interval, this serving as a source for modulation of visual attention, decreasing it when no relevant event was expected and increasing it before onset of an event. Induced alpha rhythm synchronization at the middle of the interstimulus pause, which was clearly more marked in plastic forms of the set and in trials in which the facial expression was correctly recognized, was a measure of top-down inhibitory control, suppressing the influences of irrelevant stimuli on the cortex. The dynamics of the theta rhythm during the interstimulus pause evidently result from the emotional memory factor due to recognition of the negative facial expression.