For years, scientific studies suggested that smarts were mostly heritable and fixed through young adulthood—nothing one could willfully boost. But some recent studies hint that a segment of smarts, called fluid intelligence—where you use logic and patterns, rather than knowledge, to analyze and solve novel problems—can improve slightly with memory exercises. The alluring finding quickly gave life to a $1 billion brain training industry [Ad blocker needs to be turned off]. This industry, including companies such as Lumosity, Cogmed, and NeuroNation, has since promised everything from higher IQs to the ability to stay sharp through aging. The industry even boasts that it can help users overcome mental impairments from health conditions, such as attention deficit hyperactivity disorder (ADHD), traumatic brain injury, and the side effects of chemotherapy.

Those claims are clearly overblown and have been roundly criticized by scientists, the media, and federal regulators. Earlier this year, Lumosity agreed to pay $2 million to the Federal Trade Commission over claims of deceptive advertising. The FTC said Lumosity "preyed on consumers' fears about age-related cognitive decline." In the settlement, the FTC forbid the company from making any such claims that the training could sharpen consumers' minds in life-altering ways.

In a study designed to assess the experimental methods of earlier brain-training studies, researchers found that sampling bias and the placebo effect explained the positive results seen in the past. "Indeed, to our knowledge, the rigor of double-blind randomized clinical trials is nonexistent in this research area," the authors report. They even suggest that the overblown claims from brain training companies may have created a positive feedback loop, convincing people that brain training works and biasing follow-up research on the topic.