Unriddling the Neural Circuitry of Impulse Control

Animals, including humans, display a range of impulsive behaviours. For example, sometimes we are unable to withhold ourselves from carrying out certain actions, even though we are aware that such actions will incur negative consequences. This type of impulsive behaviour is attributed to the alcoholic whom is perfectly aware that drinking is leading him down a path of self-destruction, but he is nevertheless incapable to withhold himself from engaging in such a behaviour. This type of behaviour is called “impulsive action” as it pertains to an individual’s inability to control their own imminent actions. Another type of impulsive behaviour is named “impulsive choice”. This type of behaviour pertains to an individual’s predisposition to overvalue and choose immediate but smaller rewards, over larger but delayed rewards. An example of this is the marshmallow test; wherein a child is presented with a marshmallow and told that if he does not eat it, he will later obtain more marshmallows. Impulsive children would rather eat one marshmallow now, than wait to obtain a larger reward later. It is important to understand that displaying impulsive behaviour is natural and it is only when it is overly expressed that it becomes detrimental to the individual. ADHD, drug addiction, bipolar disorder, problem gambling and eating disorders are disorders wherein impulsive behaviour is no longer being properly controlled.

Both types of impulsive behaviour are thought to be mediated by different neuronal circuits within the brain. Although we have some understanding of the circuitry already, the aim of this thesis was to further tease out these circuits. This was done by using precise methodologies which enabled us to target specific areas and connections within the brain with time locked precision. The experiments were performed in rats trained in tasks wherein they would have to wait for a cue before making a response or choose between a small immediate reward or larger but delayed reward. By using lasers (amongst other techniques) to stimulate neurons within the brain we were able to pinpoint the role of distinct circuits in not only impulsive behaviour but also attentional behaviour.