For many years it was believed by medical science that neuroplasticity, the phenomenon in which the human brain rapidly and readily creates neuronal interconnections tapered off as people got older. Children are renowned for learning anything and everything that catches their fancy (not always what we'd wish they'd learn) but the learning process seems to slow down the older they get. As adults, it's much harder to learn complex new skills from scratch. In recent years, a number of compounds have been developed that seem to kickstart neuroplasticity again, but they're mostly used for treating Alzheimer's Disease and not so readily as so-called smart drugs. However, occasionally an interesting clinical trial pops up here and there. Enter donepezil: A cholinesterase inhibitor which increases ambient levels of acetylcholine in the central nervous system. At Boston Children's Hospital not too long ago, Professor Takao Hensch of Harvard University administered a regimen of donapezil to a 14 year old girl being treated for lazy eye, or subnormal visual development in one eye. Similar to using valproate to kickstart critical period learning in the auditory cortex, administration of donepezil seems to have caused the patient's visual cortex to enter a critical period of learning and catch up to the neural circuitry driving her dominant eye. The patient's weaker eye was measurably stronger and her vision was measured to be more acute than before the test program began. What is not clear is whether this is a sense-specific improvement (i.e., does donepezil only improve plasticity in the visual cortex, or will it work in a more wholeistic way upon the human brain). It's too early to tell, and we don't yet have enough data, but the drug's clinical use for treating Alzheimer's seems to imply the latter. Definitely a development to monitor because it may be useful later.
As I mentioned earlier, children are capable of learning incredibly rapidly. This is in part due to neural plasticity, and in part due to a burning curiosity about the world around them which comes from being surrounded by novelty. When one doesn't have a whole lot of life experience, the vistas of the world are bright, shiny, and new. Growing older and building a larger base of knowledge upon which to draw (as well as the public school system punishing curiosity in an attempt to get every student on the same baseline) dims curiosity markedly, and it's hard to hang onto that sense of wonder and inquisitiveness the older one gets. Dr. Matthias Gruber and his research team at U.Cal Davis have been studying the neurological phenomenon of curiosity and their work seems to shore up something that gifted and talented education teachers have been saying for years. In a nutshell, when someone is curious about the topic of a question they are more likely to retain the information for longer periods of time because the mesolimbic dopamine system - the reward pathways of the brain - fire more often, and consequently increase activity in the hippocampus, which is involved in the creation and retrieval of long term memories. To put it another way, if you're interested in what you're learning, you're going to enjoy learning, and consequently what you're learning will stick better. So, what do we do with this information? It seems to inform some strategies for both pedagogy and autodidactism in that it seems possible that it would be easier to learn something less interesting by riding the reward system "high" by studying something more captivating in tandem. Coupled with a strategy of chunking (breaking a body of information into smaller pieces which are studied separately) it might be possible to switch off between more interesting and less interesting subjects in a study session and retain the less interesting stuff more reliably. This is pretty much one of the strategies I used in undergrad; while I didn't gather any metrics for later review and analysis, I did just this when studying things that I found less interesting or problematic and definitely did better on exams and final grades. One thing I did notice is that the subject matter could not be too wildly different; alternating calculus and Japanese didn't work very well, for example, but calculus and computational linguistics worked well together. Experimenting with such a strategy is left as an exercise for the motivated reader.