Recognition that ADHD persists into adulthood has substantially increased the prescription stimulant treatment of adults with the disorder (see above). It has also resulted in a corresponding escalation of nonprescription stimulant use in many college students confirmed by numerous surveys. Studies consistently show that students report using stimulant medications, legally or illicitly, to improve academic performance, specifically to increase concentration and the ability to stay up longer and study. Intuitively, it would seem logical that drugs that improve attention and concentration should also promote learning and academic achievement. Inherent in terms like “cognitive enhancers,” “smart drugs,” and “neuroenhancers” is the assumption that MPH and d-AMP enhance cognition. Major magazines such as The New Yorker
have reported a trend toward growing use of prescription stimulants by college students for “neuroenhancement”. In fact, some students are faking ADHD to gain access to prescription stimulant medication, which has led to a shortage of ADHD drugs such as Adderall (Mitchell 2012
). Unfortunately, media reports appear to condone this behavior as 95% of articles mentioned at least one possible benefit of using prescription drugs for neuroenhancement, but only 58% mentioned any risks or side effects (Partridge et al. 2011
). Duke University recently enacted a new policy prohibiting the nonmedical use of prescription stimulants for any academic purposes (McLaughlin 2012). Students received an email stating policy changes including, “The unauthorized use of prescription medication to enhance academic performance has been added to the definition of Cheating.” In the past, the use of such drugs without a prescription was only a violation under the University's drug policy. Oddly, the assumption that prescription stimulants are truly “cognitive enhancers” is not really questioned. Stimulants reduce hyperactivity, impulsivity, and inattention in children and adults with ADHD, so it has been assumed that these drugs enhance long-term intellectual performance. However, contrary to simple implicit assumptions found in bioethics and media discourses, there are actually only a few studies on the enhancement effects of “cognitive enhancers” in individuals without ADHD.
Smith and Farah (2011
) reviewed data on prescription stimulants as neuroenhancers from over forty laboratory studies involving healthy, nonelderly adults. Most of the studies looked at one of three types of cognition: learning, working memory, and cognitive control. Effects of d-AMP or MPH on cognition were assessed by a variety of tasks (). A typical learning task asks subjects to memorize a list of paired words; an hour, a few days, or a week later, subjects are presented with the first words in the pairs and asked to come up with the second. In general, with single exposures of verbal material, the studies on learning showed that no benefits are seen immediately following learning, but later recall and recognition are enhanced. Of the six articles reporting on memory performance (Rapoport et al. 1978
; Soetens et al. 1993
; Camp-Bruno and Herting 1994
; Fleming et al. 1995
; Unrug et al. 1997
; Zeeuws and Soetens 2007
), encompassing eight separate experiments, only one of the experiments yielded significant memory enhancement on short delays (Rapoport et al. 1978
). In contrast, retention was reliably enhanced by d-AMP when subjects were tested after longer delays, with recall improved after 1 h through 1 week (Soetens et al. 1993
; Zeeuws and Soetens 2007
). These data suggest that when people are given rote-learning tasks their performance is improved by stimulants. The benefits were more apparent in studies where subjects had been asked to remember information for several days or longer. However, studies only found a correlation with rote memory tasks, not complex memory, which is more likely to appear on college exams.
Overview of effects of prescription stimulants on cognitive performance in adults without ADHD
In contrast to the types of memory, which are long lasting and formed as a result of learning, working memory is a temporary store of information that plays a role in executive function. Several studies have assessed the effect of MPH or d-AMP on tasks examining various aspects of working memory (Sahakian and Owen 1992
; Oken et al. 1995
; Elliott et al. 1997
; Mehta et al. 2000
; Barch and Carter 2005
; Silber et al. 2006
; Clatworthy et al. 2009
) (see ). One classic approach to the assessment of working memory is the span task, in which a series of items is presented to the subject for repetition, transcription, or recognition. A spatial span task, in which the subjects must retain and reproduce the order in which boxes in a scattered spatial arrangement change color was employed by Elliott et al. (1997
) to assess the effects of MPH on working memory. For the subjects in the group who received placebo first, MPH increased spatial span. However, for the subjects who received MPH first, there was a nonsignificant opposite trend. The authors noted that the subjects in the first group performed at an overall lower level, and so, this may have contributed to the larger enhancement effect for less able subjects. Barch and Carter (2005
) obtained similar results and Mehta et al. (2000
) found evidence of greater accuracy with MPH. In the study by Mehta et al. (2000
), the effect depended on subjects' working memory ability: the lower a subject's score on placebo, the greater the improvement on MPH. In contrast to the three previous studies, Bray et al. (2004
) reported that MPH does not improve the cognitive function of sleep-deprived young adults. In sum, the evidence concerning stimulant effects of working memory is mixed, with some findings of enhancement and some null results, although no findings of overall performance impairment (Smith and Farah 2011
). However, the small effects were mainly evident in subjects who had low cognitive performance to start with, showing that the drug is more effective at correcting deficits than “enhancing performance.” Farah et al. (2009
) recently examined the effect of Adderall upon creativity, a component of cognition stimulants are suspected of stifling, in a double-blind, placebo-controlled trial. They found that the drug enhanced creativity on specific tasks, but the amount of enhancement depended upon the baseline performance of individuals: lower-performing individuals were more enhanced than high-performers. Thus, the drugs do not offer as much help to people with greater intellectual abilities.
The third type of cognition is cognitive control. Cognitive control is a broad concept that refers to guidance of cognitive processes in situations where the most natural, automatic, or available action is not necessarily the correct one (Smith and Farah 2011
). Attention and working memory are thought to rely on cognitive control and loss of cognitive control is a major component of many neuropsychiatric diseases such as schizophrenia. The effects of MPH and d-AMP have been determined on several tests used to study cognitive control, including the go/no-go task, the stop-signal task, and the Flanker test. In general, the effects of stimulants on cognitive control are not robust, but MPH and d-AMP appear to enhance cognitive control in some tasks for some people, especially those less likely to perform well on cognitive control tasks (Smith and Farah 2011
). The results of these studies currently provide limited support for the enthusiastic portrayals of cognitive enhancement.
The neural basis of error processing has become a key research interest in cognitive neuroscience. Recently, a single dose of MPH was shown to improve the ability of healthy volunteers to consciously detect performance errors (Hester et al. 2012
). Furthermore, this behavioral effect was associated with a strengthening of activation differences in the dorsal anterior cingulate cortex and inferior parietal lobe during the MPH condition for errors made with versus without awareness. How the brain monitors ongoing behavior for performance errors is a central question of cognitive neuroscience. Diminished awareness of performance errors limits the extent to which humans engage in corrective behavior and has been linked to loss of insight in ADHD and drug addiction.
As it remains unclear whether stimulant medication has the same effect on healthy individuals as for those with ADHD, it is possible that many reported effects of prescription stimulants in healthy individuals may stem from placebo effects. Looby and Earleywine (2011
) examined whether placebo effects influence reports of subjective mood and cognitive performance among college students who endorsed several risk factors for prescription stimulant misuse (e.g., low grade point average, fraternity/sorority involvement, binge drinking). Interestingly, participants believed that they had better ability to focus and persevere, particularly for a sustained amount of time, when they expected to receive MPH (Looby and Earleywine 2011
). This is similar to circumstances in which participants may engage in nonmedical-stimulant use to study or cram for extended hours. On the other hand, when experimental participants did not expect to receive MPH, their attention appeared disrupted resulting in inconsistent reaction times throughout the CPT. Interestingly, subjective feelings of being high and stimulated were produced solely by expecting to receive MPH. This finding is important to consider when examining initiation and maintenance of nonmedical prescription stimulant use. As motives for nonprescription stimulant use include the desire to feel high (Barrett et al. 2005
), it is likely that individuals who use a stimulant for this purpose will consequently feel high due to these demonstrated placebo effects, which will likely maintain misuse of the drug.