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Neurocognitive endophenotypes of impulsivity and compulsivity: towards

dimensional psychiatry

Trevor Robbins, Claire Gillan, Dana Smith, Sanne de Wit, and Karen Ersche

The authors of this article aim to fix the problem of the lack of biological footing in the

DSM by encouraging a new approach to psychiatry based on neurocognitiveendophenotypes.

Currently, diagnoses in clinical psychology can be difficult due to complex and

heterogeneous symptoms in any given disorder combined with the array of

comorbidities and other disorders a patient may have. DSM criteria are often based

more upon descriptions of superficial behavioural signs and verbal reports of patients

and associates rather than being rooted in biology.

Neurocognitive endophenotypes are well-defined behavioural or cognitive processes

associated with discrete deficits in defined neural systems. Often these present in

first-degree relatives of patients due to genetic components. Methods involving theseendophenotypes allow for early detection of disorders, avoid exclusive uses of clinical

rating scales, and deal with the issue of comorbidities and multiple diagnoses. The

article focuses on a broad range of disorders: substance dependence, OCD, ADHD,

eating disorders all of which could be labeled impulsive-compulsive disorders.

Impulsivityis a trait leading to actions which are poorly conceived, prematurely

expressed, risky or inappropriate to the situation and that often result in negative

consequences. Compulsivityis similar to Impulsivity in that it involves a failure of

response inhibition. However, it leads to actions inappropriate to the situation which

persist and have no obvious relationship to the overall goal.

OCD

OCD patients and their families are predisposed to Tourettes syndrome. They share

common dysfunctions in frontal-striatal circuits and various other deficits rooted in

biological causes. These deficits provide a potential biological basis for compulsivity

as a neurocognitive endophenotype.

Drug addiction

Impulsivity and compulsivity are both evident in drug-dependent individuals. High

impulsivity is predisposing for the development of compulsive drug-taking as seen in

animal and human studies detailed in the article. Drug users and their siblings both

rate high in impulsivity, which could indicate a familial vulnerability. This fitsendophenotype criteria and indicates a genetic basis. Drug users and their siblings

were also found to be almost equivalently impaired on a test of response inhibition

which involves white matter changes.

ADHD

Impulsivity is a key symptom of ADHD. ADHD patients have a propensity for drug

abuse as the disorder is highly comorbid with drug-dependency.

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OCD and Drug Dependence

The compulsive nature of drug abuse is supported by similarities in brain structure

and functional abnormalities that are found in both substance dependent individuals,

and OCD patients (such as decreases in OFC gray matter density). Drug-dependent

individuals and their non-dependent siblings report high levels of obsessive-compulsive behaviour indicating an underlying factor or endophenotype.

OCD, Substance abuse, and Compulsive Eating Disorders

There is high comorbidity between drug use and binge eating. The conditions share

numerous behavioural and physiological similarities, and diagnostic criteria. Both are

characterized by altered activity of the midbrain dopaminergic system and various

other physical changes.

Conclusion

Due to the common behaviours and biological traits seen among substance users,

compulsive eaters and patients with OCD or ADHD, the authors argue that there is astrong case for an underlying link between these disorders. Eventually, tests of

compulsivity and impulsivity will hopefully enhance diagnostic systems such as the

DSM by providing objective, quantitative assessments of impulsive-compulsive

syndromes.

Discussion:

Do Robbins et al. have sufficient evidence to claim the existence of these

neurocognitive endophenotypes? Why or why not? Does a fully objective system

ignore the value of the insights of experienced clinicians?

Drug addiction, gambling, and eating disorders are not higher in OCD patients.Robbins et al. claim this lack of comorbidity does not necessarily mean they dont all

stem from a common endophenotypes as they could be expressed in superficially

contrasting ways. Considering the fact that correlations would be expected if there

were an underlying factor, is the authors justification adequate?

Multiple Choice Question:

Which of the following characteristics is a trait associated with the neurocognitive

endophenotype of compulsivity and NOT impulsivity:

A Action performed is inappropriate for situation

B Action leads to undesirable consequences

C Major component of drug dependenceD Failure of response inhibition (top-down control)

E Actions persist without specific goals