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.