Social threat perception and the evolution of paranoia.

Rapid and efficient judgments about the significance of social threat are important for species survival and may recruit specialized neurocognitive systems, consistent with biological models of threat processing. We review cognitive, psychophysiological, neuropsychological, and neuroimaging evidence in support of specialized neural networks subserving the processing of facial displays of threat. Cognitive research suggests that faces depicting anger are detected quickly when presented amongst other facial expressions, on the basis of distinguishing facial features. Psychophysiological investigations using visual scanpath techniques provide evidence for increased foveal attention to facial features of threat-related expressions (anger, fear), which may facilitate rapid detection and subsequent appraisal of the significance of threat (such as the direction of impending threat). Neuropsychological and neuroimaging studies implicate a primary role for the amygdale and pre-frontal cortices in interpreting signs of danger from facial expressions and other social stimuli. Subtle disturbances in these neurocognitive systems underlying efficient threat detection (manifesting in attentional biases and aberrant neural activity) may result in abnormally heightened perception of social threat, as seen in clinical levels of social anxiety and/or persecutory delusions in schizophrenia. Clinical states of paranoia may therefore reflect normal variation (i.e. biases) in the adaptive mechanisms which have evolved, in the Darwinian sense, to facilitate efficient threat detection in humans. As such, clinical levels of paranoia may represent the inevitable cost of efficient threat perception--or 'justified' suspicion--that is necessary for survival of the human species.