DMAE, or dimethylaminoethanol, is a compound found in high levels in anchovies and sardines. Small amounts of it are also naturally produced in the human brain. Health-food outlets sell it in capsule form to "boost brain power." It probably won't make you smarter, but some evidence suggests it may have benefits against the impulsive and disruptive behaviors caused by attention deficit hyperactivity disorder (ADHD). It may also have a role in treating memory lapses and Alzheimer's disease, as well as some troubling movement disorders.
The supplement has an interesting history. Initially, drug makers were interested in selling the product as a medication for attention deficit disorder when studies in the 1970s showed that deanol, the chemical name for DMAE, reduced hyperactivity and improved concentration in schoolchildren with learning disabilities and behavior problems. However, when further testing was deemed too expensive, it was packaged as a nutritional supplement, since this substance is naturally found in fish.