Research on marmosets as reported in The Conversation has revealed the role that a region of the brain called sgACC plays in emotional arousal. Over-activity of sgACC was already associated with the dampening of pleasure and reward stimulus, seen in depression.
A threat was presented to the marmosets in the form of a rubber snake and the marmosets were conditioned with a tone to create an association. The tone was later made without the snake to de-associate it from threat. The experimental group had over-activity induced in sgACC, the control group did not.
They found that marmosets who had not had sgACC over-stimulated responding normally to the de-association, calming down more quickly, but the over-activity group displayed fear and elevated blood pressure for much longer.
The over-activity of sgACC was also linked to abnormal heart function – increased heart rate and reduced variability in heart rate even at rest, without the presence of a threat.
Such changes reflect the presence of anxiety. The abnormal heart rates suggests that sgACC promotes the “flight or fight” response.
Brain imaging showed, with over-activity in sgACC, concurrent increased activity in the amygdala and hypothalamus, and reduced activity in the lateral prefrontal cortex, which is also seen in depression. Ketamine, a drug being investigated to treat depression, was shown to treat the depression aspects of sgACC over-activity, but in this case not anxiety – the marmosets remained fearful to stimulus.
