Neurophysiological correlates of subjective significance

Objective The neural substrates of emotional response have traditionally been studied using universal sets of emotionally loaded stimuli, regardless of their subjective significance for the individual subject. Related brain activity has been typically traced with fMRIʹs temporal resolution of seconds. In this study, unique brain responses to subjectively significant stimuli were analyzed and traced with millisecond temporal resolution. Methods Electrical brain activity (event related potentials) was recorded from 16 normal subjects, to subjectively significant auditory stimuli and its brain sources were imaged. Subjective significance of the stimuli was individually assessed for each subject. Results Unique and significant brain activity to subjectively significant stimuli began as early as 200 ms after stimulus onset, with increased brain activity in the vicinity of several brain areas, including frontal gyri, Brocaʹs area, Wernickeʹs area, insula, precuneus and cingulate gyri. The time course of activity in these areas was traced and found concurrent. Conclusions Although the subjectively significant stimuli of this study were not divided according to their positive or negative affective valence, they elicited a distinct brain response compared to neutral stimuli, with a uniform pattern across subjects. Significance These results demonstrate that subjectively significant stimuli are associated with characteristic brain activity, that studying the neural substrate and time course of processing subjectively significant stimuli is feasible and that the neurophysiological manifestations of emotions are attainable.