Neural mechanisms underlying selective attention to threat.

Biased competition models of selective attention suggest that attentional competition is influenced both by bottom-up sensory mechanisms sensitive to stimulus salience and top-down control mechanisms that support the processing of task-relevant stimuli. This provides a framework for investigating the neural mechanisms underlying selective attention to threat. Both subcortical regions implicated in threat detection--specifically the amygdala--and prefrontal cortical regions implicated in top-down attentional control are activated in response to task-irrelevant threat stimuli. A number of questions including the automaticity of the amygdala response to threat distractors, the modulation by anxiety of the amygdala and prefrontal response to these stimuli, and the impact of genetic and environmental factors upon this circuitry are addressed. The empirical literature is considered in the context of theoretical accounts of the neural substrate of selective attention and conscious awareness. It is suggested that the neural activity provoked by a given visual stimulus is influenced by factors impacting upon the strength of the bottom-up trace (e.g., presentation time, backward masking), stimulus salience (including threat relatedness), competition with other visual stimuli for perceptual processing resources, and the augmentation of the stimulus trace by allocation of top-down attentional resources. Individual differences in trait and state anxiety, and in genetic makeup, are thought to modulate the influence of stimulus valence and top-down attention through their impact upon amygdala and prefrontal function.