Comment: Affective Chronometry Has Come of Age

An individual's affective style is influenced by many things, including the manner in which an individual responds to an emotional challenge. Emotional response is composed of a number of factors, two of which are the initial reactivity to an emotional stimulus and the subsequent recovery once the stimulus terminates or ceases to be relevant. However, most neuroimaging studies examining emotional processing in humans focus on the magnitude of initial reactivity to a stimulus rather than the prolonged response. In this study, we use functional magnetic resonance imaging to study the time course of amygdala activity in healthy adults in response to presentation of negative images. We split the amygdala time course into an initial reactivity period and a recovery period beginning after the offset of the stimulus. We find that initial reactivity in the amygdala does not predict trait measures of affective style. Conversely, amygdala recovery shows predictive power such that slower amygdala recovery from negative images predicts greater trait neuroticism, in addition to lower levels of likability of a set of social stimuli (neutral faces). These data underscore the importance of taking into account temporal dynamics when studying affective processing using neuroimaging.

The ability to simultaneously acquire objective physiological measures of emotion concurrent with fMRI holds the promise to enhance our understanding of the biological bases of affect and thus improve our knowledge of the neural circuitry underlying psychiatric disorders. However, the vast majority of neuroimaging studies to date examining emotion have not anchored the examination of emotion-responding circuitry to objective measures of emotional processing. To that end, we acquired EMG activity of a valence-sensitive facial muscle involved in the frowning response (corrugator muscle) concurrent with fMRI while twenty-six human participants viewed negative and neutral images. Trial-by-trial increases in corrugator EMG activity to negative pictures were associated with greater amygdala activity and a concurrent decrease in ventromedial PFC activity. Thus, this study highlights the reciprocal relation between amygdalar and ventromedial PFC in the encoding of emotional valence as reflected by facial expression.