Psychopaths have a bad sense of smell

     Researchers at Sydeny's Macquarie University tested a theory that psychopathy - a severe personality disorder characterised by lack of empathy, antisocial behaviour and callousness - may be linked to impaired smell ability.

     Bothe phenomena have been independently traced to dysfunction in part of the brain called the orbito-frontal complex (OFC).  MehmetMahmut and Richard Stevenson of the Department of Psychology at Macquarie University trialled the olfactory sills of 79 individuals, aged 19 to 22 who had been diagnosed as non-criminal psychopaths and lived in the community.

     Using "sniffin" Sticks" - 18 pens that contain differnt scents such as orange, coffee and leather - they found the pasrticipants had problems in correctly identifying the smell, and then discriminasting it against a different odour.  Those who scored highest on a standard scorecard of psychopathic traits did worst on both counts, even though they knew that they were smelling something.

     Olfactory measures represent a potentially interesting marker of psychopathic traits, because performance expectancies are unclear in odour tests and may therefore be less susceptible to attempts to fake good or bad responses.  The OFC is a front part of the brain responsible for controlling impulses, planning and behaving  in line with social norms.

     It also appears to be important in processing olfactory signals, although the precise function is unclear, according to previous research.  From there, the signals go to OFC via a brain organ called the mediodorsal nucleus, located in the thalamus.  The study makes clear that a poor ense of smell does not by itself mean that someone is a psychopath.  Olfactory dysfunction can also occur in schizophrenia, Parkinson's and Alzheimer's disease, it notes.