What we don't know about cognitive enhancement

The use of prescription drugs such as Ritalin, Adderall and Provigil for increasing attention and work capacity has been controversial. However, in the context of such back and forth fights about the desirability of pharmaceutical cognitive enhancement, we must step back and ask some basic scientific questions:
- Do these drugs enhance brain function in people without ADHD or narcolepsy?
- Do they work equally well in everyone?
- Are there any cognitive trade-offs for using these drugs?

This is why this review by Husain and Mehta is both timely and important. Some of the great points made include:

1. We do not understand cognitive systems well enough to understand the potential trade-offs that may exist from taking a cognitive enhancing drug. There are counter-intuitive findings everywhere. For example, young adults who carry the APOE-4 allele (which has been associated with a higher risk of dementia later in life) actually have better performance on decision making tasks than those carrying the APOE-3 version. Therefore, it is plausible that drugs targeting memory systems might have detrimental effects on decision making tasks.

2. It's difficult to know how well cognitive enhancing drugs work in healthy people in the "real world". Although several studies have shown increased performance for certain laboratory tests of cognitive ability, there is no clear consensus about how these tasks translate into real-world academic or job performance. Furthermore, as most studies show small effect sizes and results in some, but not all tasks, there is a very real possibility that these drugs have no measurable effect outside of the laboratory.

3. A small overall cognitive enhancing effect of a drug can come either from a small effect observed in all participants, or large effects in some participants and no effects in others. Previously, these authors have shown large individual difference in cognitive enhancers (I wrote about this here). In particular, participants with lower working memory capacity seem to have more enhancement from these drugs than those with larger working memories.

4. A common complaint, but relevant nonetheless: the long-term effects of these drugs, taken for enhancement purposes, is unknown.

What I particularly like about this paper is that it both outlines a needed future research plan while staying above the ideological ethical fray.  

Husain M, & Mehta MA (2011). Cognitive enhancement by drugs in health and disease. Trends in cognitive sciences, 15 (1), 28-36 PMID: 21146447