Neurology of OCD



 A number of brain areas have been implicated in OCD, in particular a loop of overactivity in three areas that trigger fear and an urge to do something, a feeling that something is wrong and a feeling of unease on which attention is fixed.  If someone with a hand-washing compulsion is asked to imagine themselves in an unclean place these brain areas fire frantically.  A similar brain pattern in a person without OCD can be produced only if they are asked to think very hard about a major catastrophe such as, their home burning down with their loved ones inside (Carter, 1998).  Just considering this information it becomes clear as to why the compulsions to obey the obsession and relieve this degree of anxiety are so very intense and difficult to break out of.


The loop of overactivity implicated in OCD with the use of brain imagery, runs between the basal ganglia, the orbital prefrontal cortex and the prefrontal/cingulate cortex. 

The OCD loop of neural activity.  The basal ganglia (A), the orbital prefrontal cortex (B) and the cingulated cortex (C).



The orbital frontal cortex is an area at the front of the brain that fires when something contrary to our expectations occurs, providing a human error detector. 




Behavioural Physiologist E.T. Rolls and colleagues taught Rhesus Monkeys that when they licked a tube after a blue light illuminated, they would receive their favourite tipple, blackcurrant juice.  With brain imaging technology Rolls identified that the Monkey's OFC became active as soon as the blue light came on.  The signals were then changed so that green meant juice and blue meant salt water.  When the monkeys next saw blue, licked the tube and received salt water their OFC fired rampantly.  The firing quietened only when the monkeys corrected their responses, stopped licking the tube when the blue light came on and tried other options, thereby shifting their attention and focus onto something else. 


A firing OFC alerts us when something has gone wrong in the world around us and our expectations and reality are out of kilter.  The area also controls our impulses giving us the ability to inhibit our behaviour or the desire to act.  Overactivity in this area explains why people with OCD feel things are ‘not right’ and have an overwhelming desire to act to correct this feeling by completing a compulsive behaviour e.g. hand washing. 




The second overactive part of the brain explains the fear, panic and terror experienced in OCD when the error detection system is activated.  The OFC is connected to the brains emotional centre, the limbic system, more specifically the Caudate Nucleus and Putamen, together known as the striatum or basal ganglia. This area receives information from the pre-frontal cortex and the amygdala among other brain areas.  The amygdala is also located in the limbic system and is the part that generates fear or the flight or fight response.  The caudate nucleus is involved in controlling thought and emotion, and the putamen stores procedural memories of automatic behaviour (e.g. riding a bike), and is involved in controlling motor activity and movement.  These areas therefore trigger the urge to do something together with the fear, anxiety and general feeling of unease felt by those with OCD.




The third overactive part of the brain is the cingulate cortex, an area in the midbrain that registers conscious emotion and is involved with keeping our attention fixed on a certain stimulus or trigger.  For people with OCD this means that their attention is fixed on the trigger for their OCD, and the emotional fear and anxiety response coming up from the basal ganglia or emotional brain.




To put these areas into context lets look at someone whose OCD involves washing their hands to protect themselves from germs.  As they see or feel some area of dirt or contamination these three brain areas will fire frantically.  The orbital frontal cortex identifies that something is wrong with the error detection system, and heightens the urge to act.  This signal is sent to the limbic system that triggers fear and anxiety together with an insatiable urge to do something about the dirt or contamination. This feeds into the cingulate cortex that keeps attention on the dirt and the feeling of anxiety and fear.  With all these areas feeding to and from each other when a person with a hand-washing obsession sees or feels dirt or contamination, it is no surprise that they will be compelled to wash their hands.  With a strong belief that washing their hands will keep them safe and eliminate any contamination, only this action will convince the brain that the danger has passesd and enable the deactivation of the error detection loop.




It is believed that the overactivity in the three areas above occurs because one of the brains messenger chemicals dopamine produces excessive excitation in the areas, whilst another serotonin, results in a lack of inhibition of these areas. 

For further information please see the books, The Mind & The Brain by Jeffrey .M. Schwartz, M.D., and Mapping the Mind by Rita Carter.