OCD is a chronic, long-lasting disorder in which a person has uncontrollable, reoccurring thoughts, described as obsessions and behaviors – or compulsions – which they feel the urge to repeat again and again. Severe cases are considered mental health disorders and can lead to loss of work and relationships, as well as social isolation and, in extreme cases, suicidal thoughts.
Scientists analyzing the brains of person with OCD spectrum disorder (OCD) sufferers using a highly-sophisticated MRI scanner found an imbalance between two neurochemicals in an area key to habits and decision-making.
“Those who don’t have OCD but are prone to compulsive behavior have increased levels of one of the same neurochemicals,” said the study, from researchers at the University of Cambridge. The neuroscientists behind the study hailed the discovery as a ‘major piece of the puzzle’ of understanding OCD. The study used a powerful 7-Tesla Magnetic Resonance Spectroscopy (MRS) scanner – one of only seven in the UK – at the Wolfson Brain Imaging Centre at Cambridge.
They used the sophisticated machine to scan 31 people clinically diagnosed as OCD sufferers, as well as 30 healthy volunteers as a control group.
The researchers also conducted tests and questionnaires with all participants, to gauge person with OCD spectrum disorder and habitual tendencies. We tested whether people were more prone to repeating the same responses, like a habit, or adapting their behavior to better pursue goals. Compulsions and habits are not the same, but impaired regulation of habits can be the basis of compulsions and shift people away from their goal-directed behavior,”said Professor Trevor Robbins a senior author of the study from Cambridge’s Department of Psychology.
The research team measured levels of glutamate and GABA – two major neurotransmitter chemicals – in regions of the cerebral cortex; the outermost and most highly developed part of the human brain. Glutamate is an “excitatory” neurochemical which facilitates electrical impulses that fire neurons to send information around brain networks.GABA, on the other hand, is an ‘inhibitory’ neurotransmitter which works against glutamate by dampening neural excitability, thus creating a balance.
It was additionally found that the severity of OCD symptoms, along with the inclination towards habitual and compulsive behavior, was related to higher glutamate levels in another part of the brain – the supplementary motor region.
This was found to be the case in OCD patients as well as in healthy participants with milder compulsive tendencies. The affected areas of the brain are both centrally involved in deciding the balance between our conscious goals and more automatic habits.
“The research, therefore suggests that compulsions ‘arise from a deregulated brain system for controlling habits,” said the study’s authors.
“Understanding obsessive-compulsive disorder is a central question for psychiatry. Symptoms of intrusive thoughts and repetitive rituals can confine patients to their homes for months on end; We have now shown definitive changes in these key neurotransmitters in OCD sufferers. Excess glutamate and reduced GABA is disrupting the neural circuitry in key regions of the OCD brain. Our findings are a major piece of the puzzle for understanding the mechanisms behind OCD. The results suggest new strategies for medication in OCD based on available drugs that regulate glutamate, In particular, drugs that inhibit presynaptic glutamate receptors. A presynaptic receptor is the part of a nerve cell that controls the release of neurotransmitter chemicals. Current OCD treatments are limited: whilst some sufferers with milder symptoms can benefit from anti-depressants, there are few options for those with severe symptoms. Some treatments are also extreme, such as deep-brain stimulation and even surgery to remove or alter parts of the brain. The studies’ results could now be used to guide future treatment therapies, including medication and non-invasive ‘magnetic stimulation’ through the scalp, which is already showing some promise in treating OCD,” Prof Robbins commented.
“Some treatments already target glutamate imbalance in a roundabout way. Now we have the evidence for why certain approaches seem to have some beneficial effect,” said Dr. Marjan Biria, another lead author of the study, who conducted the work in Robbins’ Cambridge lab.
Edited by Eunice Anyango Oyule and Judy J. Rotich
