Working memory has been likened to a mental scratch pad: you use it to keep relevant data in mind while you're completing a task. (Imagine a cross-examination, in which a lawyer has to keep track of the answers a witness has given and formulate new questions based on them.) In one common test subjects are shown a series of items - usually letters or numbers - and then presented with challenges: was this number or letter in the series? Was this one? In the working-memory tests, subjects performed better on neuroenhancers, though several of the studies suggested that the effect depended on how good a subject's working memory was to begin with: the better it was, the less benefit the drugs provided.
Wild salmon. Deep-water fish, such as salmon, are rich in omega-3 essential fatty acids, which are essential for brain function, says Kulze. Both she and Pratt recommend wild salmon for its "cleanliness" and the fact that it is in plentiful supply. Omega-3s also contain anti-inflammatory substances. Other oily fish that provide the benefits of omega-3s are sardines and herring, says Kulze; she recommends a 4-ounce serving, two to three times a week.
Modafinil, also known as Provigil, Modalert, and Alertec, was originally made and marketed for sleep disorders, and has been prescribed in the US for this reason since 1998. It was found only by chance to help with focus and concentration, and it is only approved for the treatment of narcolepsy, shift work sleep disorder, and obstructive sleep apnea.

The use of cognition-enhancing drugs by healthy individuals in the absence of a medical indication spans numerous controversial issues, including the ethics and fairness of their use, concerns over adverse effects, and the diversion of prescription drugs for nonmedical uses, among others.[1][2] Nonetheless, the international sales of cognition-enhancing supplements exceeded US$1 billion in 2015 when global demand for these compounds grew.[3]