Impulsivity and compulsivity are behavioural traits that may underlie a range of psychological symptoms and which cross-cut categorical mental health condition diagnoses.

This was the opening message of Professor Robbins’ plenary lecture in which he described the similarities and differences between impulsivity and compulsivity, their close inter-relationship and some of the research into understanding the drivers and mechanism for these behaviour constructs.

He started with some definitions. Professor Robbins said impulsivity describes actions that are poorly conceived and inappropriately expressed. Compulsivity refers to actions that persist inappropriate to the situation and which have no relationship to the overall good.

Coined in this way, Professor Robbins therefore highlighted that impulsivity is a term that can be used to describe the beginning of a behaviour, whereas compulsive behaviour persists maladaptively and needs to be stopped.

Restless in lectures

A ripple of laughter ran through the auditorium when Professor Robbins reminded his audience that the Barratt Impulsivity Rating Scale includes an impulsivity-defining item of “Restless in lectures.”

Impulsivity and/or compulsivity are features of a number of mental disorders and Professor Robbins gave the example of substance abuse as a situation where there is drift from impulsive to compulsive behaviour over time. He highlighted that both these behaviours are part of human reward system that is mediated by cortico-striatal machinery and he described how that reward system is influenced by a ‘hot loop’ under the influence of serotoninergic and dopaminergic pathways.

Professor Robbins described how researchers have been interested in trying to determine whether changes seen in the brain and behaviours displayed by people with chronic substance abuse, for example, are caused by the drug of abuse, or whether some people have a predisposition for such behaviours.

Focussing on impulsivity, Professor Robbins said this seems related to impaired decision-making without reflection. He suggested that in stimulant abusers or alcohol dependent people, there is some evidence to suggest that a trait of impulsivity may be a causal factor in the condition, as a well as a feature that can be created by substance miss-use.

Reaping rewards

During his lecture, Professor Robbins described animal models that have been used to study reward and punishment, to track the change in behaviour from impulsivity to compulsivity under certain conditions, and to demonstrate an endophenotype for substance abuse. He reminded delegates that impulsivity is subject to “top-down” influences from the frontal cortex, which if damaged could result in impulsive behaviours.

Turning to compulsivity, Professor Robbins noted that the mechanisms of this behaviour include motor disinhibition, enhanced habit learning, and persistence in behaviour even when there is no reward. Cognitive rigidity also contributes to compulsivity. Neurotransmitters involved in compulsive behaviour include dopamine and glutamate transmission mediated via GABA receptors.

Professor Robbins said that animal studies suggest that in compulsive behaviour, goal directed behaviour is instrumental in initiating behaviour patterns, but it is the training and repetition aspect that is the building block of compulsivity, rather than the reward / reinforcer aspect. He explained that experiments in human subjects also show that if you devalue the goal (of the behaviour), it may impair goal directed actions but people will persist in the behaviour due to habit. Then, he said, certain medications enhance habit, bringing what he called “the double-whammy.”