It’s been a lousy couple of years for researchers who study the effects of computerized brain training. In October of 2014 a group of more than seventy academics published what they called a consensus statement, asserting that playing brain games had been shown to improve little more than the ability to play brain games. “Perhaps the most pernicious claim, devoid of any scientifically credible evidence, is that brain games prevent or reverse Alzheimer’s disease,” the group stated. “No studies have demonstrated that playing brain games cures or prevents Alzheimer’s disease or other forms of dementia.” Then, this past January, the Federal Trade Commission fined Lumosity, the largest and best-known provider of online brain games, two million dollars for making what the commission considered to be unsubstantiated claims of cognitive improvement. Even as dozens of researchers, some funded by the National Institutes of Health and other reputable government agencies, continued to insist that the field was not the neuroscientific equivalent of desktop fusion or coffee colonics, the fact remained that no brain game, nor any drug, dietary supplement, or lifestyle intervention, had ever been shown in a large, randomized trial to prevent dementia. That was the case until today, when surprising new results were announced at the Alzheimer’s Association annual meeting, in Toronto.

The findings arose from the Advanced Cognitive Training for Independent and Vital Elderly (ACTIVE) study, which boasts excellent bona fides. Its nearly three thousand participants were recruited back in 1998, and since then—with $23.6 million in funding from the National Institute on Aging and an additional $10.2 million from the National Institute of Nursing Research—the study has been the subject of more than fifty peer-reviewed scientific papers. The participants, who had an average age of 73.6 at the beginning of the trial, were randomly divided into four groups. The first group, which served as control, received no brain training at all. The next two were given ten hours of classroom instruction on how to improve memory or reasoning. The last group performed something called speed-of-processing training.

Imagine that you are looking at a computer screen. For the briefest instant, two images appear—one in the middle, one on the periphery. Then the computer prompts you to identify them. Was the central image a tiny car or a little truck? Where along the edge did the second image appear? The more accurate you get, the more fleetingly the pictures appear, the more similar the car and truck get, and the more distracting the background becomes. That is speed-of-processing training. It is always one step ahead of you, yet virtually everyone gets faster and more accurate with practice.

An example of a speed-of-processing test. The training stays one step ahead of you, yet virtually everyone gets faster and more accurate with practice. Photograph courtesy Posit Science Photograph courtesy Posit Science

Ten years after ACTIVE began, researchers were still in touch with all but forty-seven of the original participants. Some had been offered four hours of additional training, and all had been followed and periodically re-tested. By then, more than three hundred met the criteria for dementia, but their odds varied significantly based on which group they had been assigned to. Among those who had been given no training whatsoever, fourteen per cent met the criteria for dementia. (That’s about half the average rate for Americans in their mid-eighties, which is not especially surprising, since the study recruited only healthy adults when it began.) The comparable rate of dementia for the speed-of-processing group was slightly lower, at 12.1 per cent. And among those who had been invited to receive the additional training, 8.2 per cent developed dementia. In all, the researchers calculated, those who completed at least some of these booster sessions were forty-eight-per-cent less likely to be diagnosed with dementia after ten years than their peers in the control group. The reasoning and memory classes, meanwhile, appeared to have no effect.

“That’s a spectacular finding,” Susanne Jaeggi, the director of the Working Memory and Plasticity Laboratory at the University of California, Irvine, and one of the signatories of the 2014 consensus statement, told me. “We didn’t have any evidence that computerized training had any preventive effects on dementia. You could argue that this study provides evidence that it is possible.” Jonathan W. King, the project scientist at the National Institute on Aging who oversaw ACTIVE, expressed a similar view. “It’s quite remarkable,” he said shortly before the study was released. “We have not found any other device or drug that changes the incidence of dementia. So, if something like this checks out, it could be very interesting.”

If it checks out. That was the cautionary refrain from King, Jaeggi, and even Heather Snyder, the senior director of medical and scientific operations at the Alzheimer’s Association. “It is one study,” she told me. “We need to see it confirmed and replicated in a larger and more diverse population.” King pointed out that the findings still need to be published in a peer-reviewed journal. And Jaeggi said that she found it difficult to understand how a dozen or so hours of playing a computerized game could have a strong and lasting influence on the brain. “If you stop doing it after ten or even fourteen sessions, how on earth can you continue to have these effects ten years later?” she asked. (One possible way, King noted, is by preserving older adults’ ability to drive a car. “The speed-of-processing training has previously been shown to reduce the risk of at-fault car crashes and the chance that older people had to stop driving,” he said. “Because it’s applicable in daily life, they may be essentially practicing it in the course of driving.”)

The lead author of the new study is Jerri Edwards, an associate professor in the School of Aging Studies at the University of South Florida. She has been investigating speed-of-processing for more than twenty years with the researcher who first conceived of it, Karlene Ball, of the University of Alabama at Birmingham. Having previously published studies showing that it improves not only older adults’ driving ability but also their capacity to perform other important activities of daily living, Edwards said that she was not surprised by the latest findings. The problem with both the public’s and many scientists’ view of brain training, she told me, is that “people lump everything together.” As ACTIVE suggests, different methods of training may have distinct benefits, or none at all. Already Edwards’s new findings have prompted the Alzheimer’s Association to update its position. In a paper published just last year, the organization said that there was enough evidence to conclude that a healthy diet, lifelong learning, and brain training may reduce the risk of cognitive decline—the kind of gradual slowing of thinking and reaction times that has long been known to begin as early as the twenties. Now, it says, brain training may also reduce the risk of dementia.

Of course, Edwards’s findings may not stand up to peer review, or they may turn out to be a fluke that cannot be replicated by others. Perhaps her central conclusion—that a dozen hours of training cuts the risk of dementia nearly in half, ten years later—will have to be walked back. And without question, a biological or behavioral explanation for how such a brief treatment can last a decade will have to be found. But still, King said, even if it documents a more modest reduction, “I’m pretty sure people would still be interested and more studies of this kind would be done.” That, after all, is how science works. People fight hard for their views, and only after Seussian towers of studies have been piled up does the evidence become overwhelming one way or the other. Then yesterday’s heterodoxy becomes today’s new consensus. Or not.