The “brain game” industry is already a billion dollar market, and will reach the $6 billion mark within the next five years says Sharp Brains, a neuro-wellness market research firm. Promising to decrease your risk of Alzheimer’s disease or boost your IQ score if you’ll just start interacting with their products online, companies like Lumosity and CogniFit are leading the charge, but upstarts are also joining the fray. In just the past few months, companies like Peak and Memorado have secured millions in funding to build or expand their online cognitive enhancement offerings.

But key questions remain: Do these programs live up to the hype? Does neuroscience, the supposed foundation of so many of these technologies, back up the idea that the right app can reduce the risk of cognitive decline? And with such a booming market in play, does anyone — consumer or investor — even care if they do?

The first two questions have been a matter of intense debate within the scientific community, but until late last year, most of the discussion had been limited to professional meetings. In October 2014, however, the Stanford Center on Longevity and the Max Planck Institute for Human Development published a public consensus statement calling out the brain game industry for deceptive marketing practices as well as a lack of scientific foundation. They stated:

We object to the claim that brain games offer consumers a scientifically grounded avenue to reduce or reverse cognitive decline when there is no compelling scientific evidence to date that they do.

The statement resulted in a handful of headlines like, “Neuroscientists come out against brain game hype” and “Brain games exploit anxieties about memory loss for profit – scientists.”

Laura Carstensen, director of the Stanford Center for Longevity, was surprised that the statement had such reach, especially since a similar statement published in 2008 had gotten little to no media attention. But in the five years since the previous statement was released, brain games had become a big business and she and her colleagues felt it was important that consumers understand the products they were purchasing.

“It just felt irresponsible to remain silent. You couldn’t turn on the radio without hearing that brain games were one of the things you had to do to maintain health as you aged. You eat right, exercise, and play brain games,” she says. “And the evidence just wasn’t there to support it.”

But others in the neuroscience world heartily disagreed. Enough that a second group of neuroscientists, led by Michael Merzenich, co-founder and chief scientific officer of popular cognitive training company Posit Science, shot back their own statement a few weeks later, arguing that there was “a large and growing body” of evidence that the brain remains plastic, or open to change, throughout the lifespan. And, as such, certain kinds of cognitive training do indeed have benefit.

Which leads back to that third question: Does anyone care? For Luminosity, it’s been business as usual. Since the last October, the company has reportedly added 10 million users, now totaling 70 million in all. Erica Perng, a spokeswoman for the company, says that neither statement has altered the company’s course in terms of product development or marketing. “We continue to plug away at making better and better cognitive training, and conducting research to better understand the most effective ways to exercise one’s mind,” she says.

Alvaro Fernandez, co-founder and analyst for Sharp Brains, agrees that the market is still booming, despite the scientific squabbling, but says the debate has caused some consternation among consumers and investors alike. “Some investors were scared by the Stanford consensus. But as they realized that this is a very diverse market and you have organizations like the U.S. Army, Pearson, and AARP making significant investments into brain fitness, they saw that it remains strong market to invest in if they find the right company,” he says.

Merzenich hopes that the discussion may attenuate what some companies do in the future — and, with luck, help separate the brain fitness wheat from the chaff. “Not every ‘brain training’ program is useful neurologically,” he says. “My hope is that people do look at the science more closely so they can differentiate the companies that have lots of science to back up what they do from the companies that don’t.”

And that may be where this debate may be of most use moving forward. As the market keeps growing and evolving, its research studies may be the most important information for investors. “And people have been paying much more attention to study findings,” says Fernandez. “Because of that we have noticed a bifurcation in funding and future development. There are some investors who mostly care about consumer traction and mobile apps, with limited attention to science. But others are focusing on very specific health, sports, and productivity applications, and those investors want a very sophisticated understanding of the evidence.”

So moving forward, the real question cognitive training companies need to answer is: Under what conditions is a particular brain training application more likely to transfer into real-world benefits? The companies that can definitively (and empirically) answer that for their users — and their investors — will look very bright.