Is emotion processed automatically? According to the prevailing view, the processing of faces with emotional content can occur without attention. In a paper published in Proceedings of the National Academy of Sciences, Pessoa et al. argue against this standpoint, presenting evidence that brain regions that respond differentially to emotional faces do so only when sufficient attentional resources are available.

Psychophysical studies indicate that visual processing outside the focus of attention is attenuated and can even be abolished. But is this true of emotional stimuli? Previous studies have indicated that emotional expressions can be processed automatically — that is, without attention. Pessoa et al. considered that the failure of these studies to detect an effect of attention on emotional processing might have been due to the failure of competing tasks to divert sufficient attention away from the emotional stimulus. To address this possibility, the authors used functional magnetic resonance imaging to measure activations in brain areas that are involved in emotional processing, and examined how these responses were modulated by attention. Importantly, they chose a competing task that would exhaust subjects' attentional resources.

A fearful, happy or neutral face was presented at the point of fixation for 200 ms, and bars were presented in the left and right periphery. In 'attended' trials — with the focus of attention on the face — subjects were asked to indicate whether the face was male or female; in 'unattended' trials, they had to comment on whether the bars were of similar orientations. Pessoa and colleagues found that, in attended trials, fearful and happy faces produced greater activations in the amygdala than neutral faces. Several other brain regions, including the fusiform gyrus, responded differentially to emotional stimuli in attended trials. However, when attention was arrested by the competing task, differential responses to emotional faces were eliminated. So, the processing of emotional expressions, like that of other visual stimuli, seems to be modulated by attention.

This study provides us with clues to the route of emotional processing by the amygdala and other brain regions. Pessoa et al. contend that the main pathway for the processing of emotional expressions is not an automatic, subcortical one; rather, they suggest that processing proceeds from the primary visual cortex to extrastriate areas, including the fusiform gyrus, and then to the amygdala.