People affected by disorders of compulsivity may share a common pattern of decision making and similarities in brain structure, according to a recent study.

Researchers from the University of Cambridge found that people  affected by binge eating, substance abuse and obsessive compulsive disorder have lower grey matter volumes (in other words, fewer nerve cells) in the brain regions involved in keeping track of goals and rewards.

"In our daily lives, we make decisions based either on habit or aimed at achieving a specific goal," researchers wrote. "However, we cannot always control the decision-making process and make repeat choices even when we know they are bad for us -- in many cases this will be relatively benign, such as being tempted by a cake whilst slimming, but extreme cases it can lead to disorders of compulsivity."

For the study, researchers compared nearly 150 individuals with disorders including methamphetamine dependence, obesity with binge eating and obsessive compulsive disorder, comparing them with healthy volunteers of the same age and gender.

Study participants first took part in a computerized task to test their ability to make choices aimed a receiving a reward over and above making compulsive choices. In a second study, the researchers compared brain scans taken using magnetic resonance imaging (MRI) in healthy individuals and a subset of obese individuals with or without binge eating disorder, a subtype of obesity.

The researchers found that all of the disorders were connected by a shift away from goal-directed behaviors towards automatic habitual choices.

The MRI scans showed that obese subjects with binge eating disorder have lower grey matter volumes -- a measure of the number of neurons -- in the orbitofrontal cortex and striatum of the brain compared to those who do not binge eat; these brain regions are involved in keeping track of goals and rewards. Even in healthy volunteers, lower grey matter volumes were associated with a shift towards more habitual choices.

 "Seemingly diverse choices -- drug taking, eating quickly despite weight gain, and compulsive cleaning or checking -- have an underlying common thread: rather that a person making a choice based on what they think will happen, their choice is automatic or habitual," Valerie Voon, principal investigator of the study, said in a statement.

The findings were recently published in the journal Molecular Psychiatry.