Neural explanations of offending behaviour focus on areas of the brain and nervous system, and the action of neurotransmitters. For example, Raine et al. (1997) found that the offender group (murderers who had pleaded not guilty by reason of insanity) showed reduced activity in areas of the brain such as the prefrontal cortex and corpus callosum (the nerve fibres responsible for swift communication between the hemispheres). There were also abnormalities in the activity of the limbic system, including the amygdala and thalamus. In terms of neurotransmitters, serotonin has been linked to mood and impulsiveness, (particularly aggression), and could also be a cause of violent crime.