Friday, February 15, 2008

Subcortical Face Processing

Johnson, M.H. (October 2005). Subcortical Face Processing. Nature Neuroscience Reviews, Volume 6, 766-774.

The most well-known visual pathway uses parvocellular channels from the retina to the LGN and on to the primary visual cortex, where very complicated fine-grained image processing is carried out. However, evidence supports multiple visual pathways, and last I checked, 12 different visual pathways have been identified in the brain so far. This review paper discusses a specific subcortical face-detection system which involves the superior colliculus, pulvinar, and amygdala.

Researchers hypothesize that this pathway is more rapid than cortical routes, relies on rather low-fidelity (low-spatial-frequency) visual information, and can critically modulate cortical processing. One characterization is that this pathway is important for directing emotional attention, providing an emotional flavoring to higher-order visual processing. As this pathway is thought to bias the cortical processing of visual input -- detecting the prescence of faces, orienting us towards them, and activating dependent cortical regions -- this may a particularly important pathway during development when cortical structures (such as the fusiform face area, orbitofrontal cortices, and other cortical regions involved in the social brain network) are still being molded. Atypical processing of socially salient stimuli, seen in such disorders as autism, Turner syndrome, and Williams syndrome, may be associated with a failures in this subcortical pathways, leading to improper development and specialization of dependent cortical circuits.

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