Thursday, June 05, 2008

Body odors - brain processing different from similar common odors

Here is an edited paste-up of text and abstract from Lundström et al.
Humans are highly accurate at identifying individuals based solely on their body odors, being able to use signals conveyed in body odor to make accurate kin–nonkin judgments, and to detect minute differences in genetic composition of unknown individuals. While visual and auditory stimuli of high social and ecological importance are processed in the brain by specialized neuronal networks, such specialized processing has not yet been demonstrated for olfactory stimuli. The authors used positron emission tomography to ask whether the central processing of body odors differs from perceptually similar non-body odors as women smelled odors collected from friends and non-friends who had slept for seven nights with tight cotton t-shirts with cotton nursing pads sewn into the underarm area. Body odors activated a network consisting of the posterior cingulate cortex, occipital gyrus, angular gyrus, and the anterior cingulate cortex, none of which is believed to be related to olfactory processing. However, together they form an interesting pattern. Posterior cingulate cortex is known to be active in response to emotional stimuli, whereas the anterior cingulate cortex is believed to regulate attentional efforts. This suggests processing of body odors is similar to what previously has been demonstrated for highly emotional stimuli, such as visual images of snakes, where the posterior cingulate cortex works in concert with the anterior cingulate cortex. A separation in the processing of odors based on their source was observed. Smelling a friend's body odor activated regions previously seen for familiar stimuli, whereas smelling a stranger activated amygdala and insular regions akin to what has previously been demonstrated for fearful stimuli.

The data provide evidence that social olfactory stimuli of high ecological relevance are processed by specialized neuronal networks, just as has been demonstrated for auditory and visual stimuli.

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