The OFC and ACC (highlighted) play a central role in inhibitory decision-making. This area is found to be abnormal in patients exhibiting OCD or addiction.

Addiction is one of the most chal­lenging and costliest problems facing society today, with signifi­cant mortality compounding annual costs from untreated substance abuse that ex­ceed a whopping $400 billion, according to the Schneider Institute for Health Policy. Scientists have investigated the neurobio­logical mechanisms underlying addiction, in hopes of creating a definitive treat­ment. Addiction is currently managed as a chronic relapsing disorder, however, a rather imprecise definition that fails to encompass the full scope of this problem. A more concrete model of addiction can, among other things, help address the ques­tion of whether addiction and other neuro­logical disorders share any characteristics that could aid in the development of suc­cessful treatment regimes for both.

The current model of addiction con­sists of two related processes. First, it ar­gues that substance use causes increased incentive in the subcortical region of the brain due to higher sensitization. In short, chronic drug use leads to neuroadaptations that sensitize the reward system to drugs, transforming ordinary wanting into exces­sive drug craving. This sensitization per­sists even after physiological dependency is eliminated (e.g. withdrawal symptoms are gone), which explains the high rates of relapse in drug addiction. This process alone accounts for the craving, desire, and preoccupation with drugs amongst addicts, but fails to explain the inability to control or regulate this behavior. The second process that occurs is impaired inhibitory control, in which addicts are unable to regulate their alcohol or drug intake despite being cogni­zant of the self-destructive consequences. This occurs due to a dysfunction in brain regions underlying inhibitory control over behavior. Specifically, two frontal regions of the brain, the anterior cingulate cortex (ACC) and the orbitofrontal cortex (OFC), are involved in evaluating the future conse­quences of one’s own actions and inhibit­ing inappropriate behaviors.

Recent studies have demonstrated that addiction and Obsessive Compulsive Disorder (OCD) share many similarities in terms of brain and cognitive impairment. OCD is a mental disorder characterized by intrusive, repetitive thoughts resulting in compulsive behaviors that the sufferer feels obligated to perform, which temporarily re­lieve the intruding thought. For example, a germaphobe who has OCD may fre­quently wash his hands for fear of contracting a bacterial infection. Interestingly, studies show that addicts and OCD patients with OFC lesions both show a disconnect be­tween knowledge and behavior in reward-based decision making tests. This means that knowledge that a behavior is maladap­tive does not preclude the sufferer from carrying it out, a key clinical feature of both OCD and addiction.

In one study, researchers measured similarities between OCD and alcoholism using the Yale-Brown Obsessive Compul­sive Scale (Y-BOCS), one of the standard measures of OCD behavior, and found sim­ilarities between obsession and compulsion in both diseases. Addiction has even been predicted with high accuracy using symp­toms of OCD. Another study used the same Y-BOCS scale to demonstrate that the level of obsessionality and compulsivity in opi­ate addiction was even higher than in al­coholism. These neuropsychological stud­ies have shown that in addiction and OCD, patients have severely affected ACC and OFC regions of the brain, responsible for inhibiting deleterious behaviors. Further­more, describing the uncontrolled compul­sive behavior of addiction in terms of OCD may also be medically relevant.

Neuroimaging studies have helped to elucidate both the similarities and dif­ferences underlying brain activity in both OCD and addiction. While dysfunction in the ACC and OFC has been reported in both conditions, metabolic activity differs depending on the stimuli provided. Under neutral conditions (e.g. if one were to ex­amine the brains of OCD suffers and ad­dicts without the influence of the intrusive thought or drug), the ACC and OFC are under-active in addiction, and over-active in OCD. This means that addicts have a limited regard for the future and high vulnerability to succumb to drug-related behaviors, whereas OCD patients are excessively concerned about the future consequences of their actions. Under prov­ocation, however, both conditions display an abnormally over-active ACC and OFC, suggesting the inhibitory system is acti­vated, yet due to the lesions, operating ab­normally. This over-activation is caused by an intense overwhelming of motivational desires, which leads to impulsivity and the tendency towards substance abuse in ad­dicts, and compulsive behaviors in OCD sufferers.

The neurobiological connection be­tween OCD and addiction will hopefully lead to clinical and therapeutic treatments for addiction. Interestingly, while current models of addiction do not include inhibi­tory dysfunction, current treatment methods and therapies incorporate techniques that target the inhibitory system. The process of motivational interviewing helps the patient explore the “pros” and “cons” of continued drug use and develop strategies to cope with cravings. Some current drug treatments, such as selective serotonin reuptake inhibi­tors (SSRI), address the model of inhibi­tory dysfunction and reduce drug intake in addicted individuals. Interestingly, SSRIs are used to treat both OCD and addiction, and these drugs are involved in delivering a rich supply of serotonin to the OFC in the inhibitory response pathway. It is clear that there is a strong connection between OCD and addiction, and a more rigorous study of both the neurobiological and behavioral similarities between the two diseases will help to deliver more successful treatment programs for addicts.