By Helen Shen
Noninvasive brain stimulation is having its heyday, as scientists and hobbyists alike look for ways to change the activity of neurons without cutting into the brain and implanting electrodes. One popular set of techniques, called transcranial electrical stimulation (TES), delivers electrical current via electrodes stuck to the scalp, typically above the target brain area. In recent years a number of studies have attributed wide-ranging benefits to TES including enhancing memory, improving math skills, alleviating depression and even speeding recovery from stroke. Such results have also spawned a cottage industry providing commercial TES kits for DIY brain hackers seeking to boost their mind power.
But little is known about how TES actually interacts with the brain, and some studies have raised serious doubts about the effectiveness of these techniques. A study published on February 2 in Nature Communicationsups the ante, reporting that conventional TES techniques do not deliver enough current to activate brain circuits or modulate brain rhythms. The electrical currents mostly fizzle out as they pass through the scalp and skull. “Anybody who has published a positive effect in this field is probably not going to like our paper,” says György Buzsáki, a neuroscientist at New York University and a senior author of the study.
The mechanisms behind TES have remained mysterious, in part because without penetrating the skull, researchers cannot measure neural responses while they apply stimulation. Conventional TES methods produce electrical noise that swamps any brain activity detected on the scalp.
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