The terms ‘impulsivity’ and ‘compulsivity’ have been used to describe a multitude of psychiatric conditions, leading researchers to question whether they reflect a shared trait. While impulsivity can refer to an action or a choice, the term often describes a trait that frequently leads to unplanned or risky behaviour. High trait impulsivity has been recognised as a risk factor for substance use disorders, and it represents a core feature of mania and disruptive behavioural disorders, such as attention deficit hyperactivity disorder (ADHD).
In contrast, ‘compulsivity’ broadly refers to the tendency to repeat a behaviour even when it may be harmful or maladaptive to the individual. This pattern of behaviour is central to obsessive-compulsive disorder (OCD), where individuals feel driven to perform mental or physical acts to reduce distress, even if those actions severely disrupt their day-to-day lives. Although not explicitly noted in current diagnostic criteria, work by Dr Samuel Chamberlain, a Wellcome Trust Fellow and Honorary Consultant Psychiatrist in the Department of Psychiatry, and others has identified elements of compulsivity in patients with trichotillomania (hair pulling), excoriation disorder (skin picking) and gambling disorder.
Interestingly, patients who develop compulsive behaviours may be inherently more impulsive. For example, preclinical neuroscience research has shown that, in rodents, heightened impulsivity predicts the development of compulsive drug-seeking and taking behaviour. Increased sensation seeking and impulsivity also relate to cocaine dependence in people.
This evidence presents a significant challenge for medical professionals, who rely on diagnostic categories to allocate resources but seek biological mechanisms to illuminate treatment targets. Dr Chamberlain explains: ‘Psychiatry has traditionally focused on defining and treating symptoms based on categories, and fixed thresholds. For example, if a person experiences a minimum number of inattentive and hyperactive/impulsive problems of childhood onset, they are labelled as having ADHD. This categorical approach is useful: it means we can measure the public health impact of a given problem and run treatment trials. For the individual, this categorical approach means that straightforward diagnoses can be made, and the person can obtain treatment.
The disadvantage of using only this approach is that nature is not so simple: many types of symptoms, associated cognitive problems, and personality traits exist on a continuum, from normal to extreme. These different levels of understanding are complementary and interrelated. The dimensional approach allows us to look ‘beneath the surface’ using all available information, to better understand the brain basis of psychiatric problems and why certain symptoms co-occur in the same individual.”
The task of integrating dimensional mechanisms with psychiatric diagnoses can be addressed, in part, by examining the full range of traits and symptoms in the general population. By doing this, researchers can acquire large amounts of data across many levels of measurement — molecular, physiological, cognitive and behavioural — and test how individual differences in these measures relates to disease status. Chamberlain and colleagues recently applied this approach to the study of impulsivity and compulsivity, aiming to identify a shared cognitive mechanism underlying the two constructs.
In their recent Psychological Medicine paper, the research team administered a wide range of questionnaires and cognitive tasks on cognition, personality and psychiatric symptoms to 576 adults. While volunteers who were currently seeking treatment for a mental health condition were excluded from the study, about 36% of the sample endorsed psychiatric symptoms in a clinical interview. When analysing their data, the team used a statistical technique to identify ‘factors,’ or latent variables that account for differences in the observed questionnaire scores and task performance. They went on to test whether one or two factors explained more of the variability in participants’ scores, where a two-factor solution would suggest that impulsivity and compulsivity reflect distinct underlying constructs.
Findings indicated that participants’ scores were indeed best explained by a two-factor solution. Moreover, the factors were moderately correlated with one another, aligning with previous evidence of the co-occurrence of these traits within the same person. Additional results showed that higher scores on either latent factor were associated with poorer quality of life. When discussing the study’s implications, Chamberlain commented:
The study shows that many types of psychiatric symptoms may be due to underlying core problems with impulsivity and compulsivity. Now that we can measure these underlying traits, we can study their basis in the brain and examine whether particular treatments can reduce them.
We hope that in the longer term this could lead to better diagnostic systems, understanding of underlying factors, and more effective treatments. For example, we have since been able to identify different predisposing factors for impulsivity and compulsivity across large numbers of individuals that can be used for early intervention.’
Taken together, this research provides support for dimensional psychiatry, but Chamberlain reminds us of the value of diversity in mental health research: ‘We need both categorical and dimensional approaches in psychiatry. We should not throw out the extensive decades of research into phenomenology and categorical diagnoses. At the same time, this approach in isolation can only go so far, and we also need latent dimensional measures incorporating different levels of understanding.’
Written by Maggie Westwater & Adrian Dahl Askelund