What is it?
OCD, or obsessive-compulsive disorder, is a mental condition that is characterized by an uncontrollable need to repeatedly check things, perform rituals, or repeat thoughts. Common manifestations include obsessing about hand washing, counting things, and checking if a door is locked. These activities have a negative impact on the lives of the affected: they often take up a considerable part of the day, and the affected often understand that they make no sense.
OCD affects around 2.3% of the population at some point of their lives, with the yearly worldwide incidence rate being 1.2%. Without treatment, OCD often lasts for decades. OCD risk seems to be unrelated to sex, and most people develop symptoms in young adulthood.
What causes it?
While the exact mechanisms are not known, both genetics and environmental factors are thought to play a role. Child abuse or other early-life stressful events are predisposing factors. A persuasive theory suggests that modest versions of OCD have had an evolutionary advantage: if it isn’t as severe as the cases we classify as disordered, it can help the individual to maintain their hygiene and keep track of enemies, for example.
What happens during it?
Three areas of the brain are closely linked to OCD. They all are more active in those with OCD, their activity increases when symptoms are provoked, and their activity decreases when OCD is treated.
The first of these three parts is the orbitofrontal cortex, OFC. It has been found to play a key role in decision making, and particularly in telling other parts of the brain what rewards or punishments can be expected after performing an action. This process is important to learning, since the brain can then compare the expected rewards/punishments with the actual rewards/punishments that followed, and adjust its attitudes towards actions. The irrational fear of getting punished for not completing an action is characteristic to OCD, so the involvement of the OFC makes sense.
The second of these parts is the anterior cingulate cortex, ACC. Its main functions include detecting and evaluating the seriousness of mistakes, especially from the emotional perspective, and suggesting a course of action. The ACC is also involved in reward-based decision making and learning.
The third of these parts is the caudate nucleus. It has many functions, but the one we’re most interested in is its role in selecting appropriate behavior based on both current goals and the knowledge of probable outcomes. I mentioned briefly before the theory that OCD is actually evolutionarily beneficial functions becoming overly active. Cleaning oneself and watching out for enemies can clearly be a positive thing. These species-specific habits have been found to reside in the basal ganglia: a structure where the caudate nucleus is located. It’s therefore quite plausible to think that OCD is caused by the increased role of these mechanisms.
How can it be treated?
Therapy forms the bulk of OCD treatment. The person is exposed to the triggers of their compulsive behavior, while not letting them react the way they normally would. Someone might, for example, be told to touch something like a tissue that has been in contact with something “contaminated” like the floor, and not wash their hands immediately afterwards. The “severity” of the trigger is increased with progress. The person learns that not performing their rituals is not, after all, so dangerous. Medication is also commonly used, and electroconvulsive therapy as well as surgery may be beneficial in severe cases.
Sources: https://en.wikipedia.org/wiki/Obsessive–compulsive_disorder#Epidemiology, https://en.wikipedia.org/wiki/Biology_of_obsessive–compulsive_disorder, https://en.wikipedia.org/wiki/Cause_of_obsessive-compulsive_disorder, https://en.wikipedia.org/wiki/Orbitofrontal_cortex, https://en.wikipedia.org/wiki/Anterior_cingulate_cortex, https://en.wikipedia.org/wiki/Caudate_nucleus