The market for noninvasive brain stimulation has received considerable attention in recent months, as new vendors have entered the market and investigators have proposed new therapies. Earlier this month, the Swedish vendor Flow Neuroscience entered the U.K. market for depression with its £399 tDCS headset. In the U.S., Bay Area startup Humm announced plans to launch its consumer tACS headset that it says improves working memory.
But despite the new opportunities, some significant challenges confront the industry, and several new research studies and journal articles have raised issues that startups will have to consider. One such report, published in Nature Communications earlier this year, suggests that the effects of tACS stimulation may result from transcutaneous stimulation of peripheral nerves in the skin as opposed to direct cortical stimulation. The report’s authors, from KU Leuven in Belgium, proposed a hypothesis that rhythmic activity from peripheral nerves indirectly entrains cortical neurons. The electric fields that penetrate the skull and reach the cortex are too weak to produce entrainment, they contend.
Whether the application is a clinical therapy such as depression or a consumer wellness benefit like improving memory, brain device vendors will need to have a better understanding of the mechanisms of action involved with their product. At the 2019 Bioelectronic Medicine Forum in New York, Kip Ludwig from the University of Wisconsin stressed the importance of understanding issues like where the current is flowing in cranial stimulation systems and how they achieve their effect. “If you don’t have target engagement and specificity you’re never going to figure out the mechanisms of action,” he said. “If you never figure out mechanisms of action you’re not going to help people or if you do you won’t be able to improve the therapy.”
One of the leading experts on transcranial electrical stimulation, Marom Bikson from the City University of New York, stresses the significance of anatomical differences in individuals, which can dramatically influence where tDCS/tACS current flows in the brain. Other investigators have addressed issues such as heating at the skin surface and the effect of electrode polarity.
In another article published in the journal Science earlier this year, two bioethicists from Penn Medicine and the University of British Columbia raised concerns about the unregulated nature of consumer neurotech products. The authors propose an independent working group to monitor these devices.
The market for noninvasive brain stimulation is poised for growth in the years ahead. But the industry must keep its roots in solid science to make that growth sustainable.
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