The part of the brain that is the hub of emotions is the limbic system. It is hidden roughly in the centre of the brain. The amygdala and the hippocampus are two of the most well-known structures. Sitting at the top of this area is the cingulate cortex. It is shown in red in the diagram above. It looks a little like a fat worm. Unlike a worm this region of the brain have neurons that connect above and below into crucial elements of the limbic system. The ACC not only process information but passes it into and out of the limbic system. The whole limbic area is significant for the experience of anxiety. For researchers interested in OCD the cingulate cortex is particularly of interest. Specifically, the section towards the front (anterior cingulate cortex) shows abnormal activity compared to people without OCD.
In 2015 Massachusetts researchers Brian Brennan and others examined the anterior cingulate cortex (ACC). They identified that the front tip of the ACC (rostral subdivision) experienced abnormal activity of neurotransmitters. Neurotransmitters provide a chemical mechanism to send signal between neurons. In overly simplistic terms the neurotransmitters are chemicals that connect two special brain cells (neurons) in the same way that a pool of water would help conduct electricity between two live wires. Specifically abnormal glutamatergic neurotransmission has been repeatedly found by a number of researchers to be a problem in this area of the brain. This study specifically identified that the glutamine to glutamate ratio was different between healthy and OCD individuals in the ACC. There are genes that help control these glutamatergic neurotransmitters and we will discover in later posts that these faulty genes for poor glutamatergic balance can be found in OCD suffers. It is no doubt overly simplistic but there is at least a plausible hypothesis to the inheritance and the expression of OCD using this pathway.
A key element of the study shows that deactivation of the rostral area of the ACC (rACC) is specific to OCD-related stimuli and was not present in emotional salient stimuli unrelated to OCD. That is an image of germs will more likely trigger the observed abnormal neurotransmitter issue than a picture of a cute cat. The researchers conclude that there is an inability to disengage attention from emotional and OCD related stimulus reducing the persons capacity at a cognitive task. That is the brain stays fixated on the fear for much longer and problem solving capabilities nosedive. Brian Brennan suggested that the fear centre (amygdala) becomes excited by an emotional OCD stimulus and the tip of the anterior cingulate cortex fails to dampen down the amygdala’s excitement. This would result in an inability to focus rationally on the stimulus and leave a heightened sense of fear. A sensation experienced by individuals with OCD.
References: An Examination of Rostral Anterior Cingulate Cortex Function and Neurochemistry in Obsessive–Compulsive Disorder Neuropsychopharmacology (2015) 40, 1866–1876 © 2015 American College of Neuropsychopharmacology. All rights reserved 0893-133X/15 Image attribution: By see below (see below) [CC BY-SA 2.1 jp (https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en)], via Wikimedia Commons Disclaimer: This content is not intended to provide medical or mental health advice. It is intended to stimulate an increased understanding of OCD. The content may not be accurate or express the views of the journal article authors.