...stimulants such as amphetamine and methylphenidate (sold under trade names such as Adderall and Ritalin, respectively) are widely used for nonmedical reasons …cognitive enhancement with stimulants is commonplace on college campuses…use by college faculty and other professionals to enhance workplace productivity has been documented…The published literature includes substantially different estimates of the effectiveness of prescription stimulants as cognitive enhancers. A recent meta-analysis suggests that the effect is most likely real but small for executive function tests stressing inhibitory control, and probably nonexistent for executive function tests stressing working memory.Farah notes several studies suggesting that the effects of Adderall and another drug, modafinil (trade name Provigil) on ‘cognitive enhancement’ are actually effects on task motivation and mood.
The newest trend in cognitive enhancement is the use of transcranial electric stimulation. In the most widely used form, called transcranial direct current stimulation (tDCS), a weak current flows between an anode and a cathode placed on the head, altering the resting potential of neurons in the current's path….Transcranial electric stimulation is expanding …with new companies selling compact, visually appealing, user-friendly devices…published literature includes a mix of findings. One recent attempt to synthesize the literature with meta-analysis concluded that tDCS has no effect whatsoever on a wide range of cognitive abilities.
Why are we so ignorant about cognitive enhancement? Several factors seem to be at play. The majority of studies on enhancement effectiveness have been carried out on small samples, rarely more than 50 subjects, which limits their power. Furthermore, cognitive tasks typically lend themselves to a variety of different but reasonable outcome measures, such as overall errors, specific types of errors (for example, false alarms), and response times. In addition, there is usually more than one possible statistical approach to analyze the enhancement effect. Small samples and flexibility in design and analysis raise the likelihood of published false positives. In addition, pharmacologic and electric enhancements may differ in effectiveness depending on the biological and psychological traits of the user, which complicates the effort to understand the true enhancement potential of these technologies. Industry is understandably unmotivated to take on the expense of appropriate large-scale trials of enhancement, given that the stimulants used are illegally diverted and transcranial electric stimulation devices can be sold without such evidence. The inferential step from laboratory effect to real-world benefit adds another layer of challenge. Given that enhancements would likely be used for years, long-term effectiveness and safety are essential concerns but are particularly difficult and costly to determine. As a result, the only large-scale trial we may see is the enormous but uncontrolled and poorly monitored trial of people using these drugs and devices on their own.