In a study in PLoS One, researchers at Leiden University and the University of Amsterdam, led by Lorenza Colzato, employed the "stop-signal paradigm" to measure the length of time taken by subjects to initiate and suppress a prepared reaction.
The stop-signal task requires participants to react quickly and accurately by pressing a left or right key in response to the direction of a left- or right-pointing green arrow. In 30% of the trials, the green arrow turned red, in which case participants had to abort the go response. The results show that while both recreational users of cocaine and non-users performed similarly in terms of response initiation, users needed significantly more time to inhibit their responses.
The study is the first of its kind to investigate systematically action control, and the inhibitory control of unwanted response tendencies in particular, in recreational users, i.e. those who don't meet the criteria for abuse or dependency but who take cocaine (usually by snorting) on a monthly basis (1 to 4 grams). The researchers found that the magnitude of the inhibitory deficit in recreational users was smaller than previously observed in chronic users, suggesting that the degree of the impairment is proportional to the level of cocaine use.
Given the seemingly small quantities of cocaine involved, the findings of this study are rather worrying. Many real-life situations require the active inhibition of pre-potent actions, as in the case of traffic lights turning red or of criminal actions. This impairment of inhibitory control has serious implications for personal or societal functioning. This reduced level of inhibitory control may even be involved in the emergence of addiction: the more a drug is used, the less able users are to prevent themselves from using it.