Neurotransmitters are responsible for relaying information from one neuron to another. If a person has low levels of serotonin then normal transmission of mood - relevant information - doesn't take place and a person may experience low moods, other mental processes may also be affected. Some cases of OCD can be explained by a reduction in the functioning of the serotonin system in the brain.
Decision making systems
Some cases of OCD (hoarding disorder) is usually associated with impaired decision making. This may then be associated with abnormal functioning of the lateral and the frontal lobes of the brain. The frontal lobes are the parts of your brain responsible for logical thinking and making decisions. There is also evidence to suggest that an area called the left parahippocampalgyrus is associated with processing unpleasant emotions, functions abnormally in OCD. (Hoarding disorder - people can't decide if they should throw something out.)
Parahippocampalgyrus
People with OCD have a dysfunctional PHG - which is associated with unpleasant emotions.
