Attention deficit and impulsivity: Driving, drugs and electrophysiology

Abstract

Impulsivity can be interpreted as a cognitive dysfunction or as a motivational dysfunction. Motivational dysfunctions are reflected in impulsive decision making such as increased preference for immediate reward over delayed more beneficial reward (delay aversion) or increased risk taking due to poor reflection on negative outcomes. Smoking is an example of impulsive decision making as it displays the tendency to choose for the immediate reward of cigarettes over reduced concern for long-term possible negative consequences. Therefore, risk taking and delay aversion were assessed in habitual smokers in relation to self-reported impulsivity. Smoking was related to motivational dysfunctions, but being a smoker in combination with being highly impulsive resulted in more extreme impulsive decisions. A disorder in which impulsivity is very prominent is Attention Deficit Hyperactivity Disorder (ADHD), which is usually treated with methylphenidate. However, 30 % of the children with ADHD do not respond to this treatment. Predicting treatment response would reduce the burden of trial-and-error treatment prescription. In the present study electroencephalographic (EEG) power measures, event-related potential (ERP) P300 amplitude, and working memory measures were obtained in 13 drug-naﶥ children with ADHD. P300 right fronto-central to parietal ratio was able to differentiate responders from non-responders. EEG power profiles suggested that responders were more cortically hypoaroused, but no significant group differences were found, possibly due to small sample size. EEG baseline measures in resting-state conditions may have the largest clinical potential in predicting methylphenidate response as these measures are easily obtained and have previously shown high accuracy in differentiating ADHD from healthy children. Although methylphenidate improves performance in ADHD, stimulants also have shown to improve cognitive performance in healthy individuals. Similarly methylphenidate improves an operational aspect of driving performance (lane keeping) in adult ADHD patients, as well as in healthy volunteers. To answer the question whether methylphenidate normalizes a decrement in lane keeping in ADHD or improves lane keeping beyond normal levels, lane keeping was compared between adult ADHD patients off-medication and healthy volunteers. The present study failed to find differences in lane keeping. Therefore we conclude that other aspects of driving, like risky, inattentive and impulsive driving may be the main cause of the increased accident rate in ADHD. In order to study inattention and distraction during driving we recorded brain potentials (ERPs) in response to irrelevant and possibly distracting events in the environment. In both simulated driving and on-the-road driving secondary auditory events did not affect driving performance. In contrast, attention orienting towards irrelevant events was reduced (as manifest in the P3a brain potential) during driving, presumably due to increased task load. Furthermore, alcohol had a dose-dependent deteriorating effect on driving performance as well as on attention orienting. Although reduced orienting of attention towards irrelevant events is useful, attention orienting towards unexpected events in the environment is necessary when the events are relevant. The method of measuring ERPs to auditory oddball stimuli during driving proved to be very useful and could be used in future research in ADHD patients, which display sub-optimal driving performance and increased distractibility, as well as the assessment of distractibility during driving in drug evaluation.