Then there are the DIY brain stimulators.
The technical term is transcranial direct current stimulation (or tDCS), and it involves hooking up electrodes to the skull and then turning on a small electric current, typically powered by a 9-volt battery.
This small but growing community cites as its inspiration studies that have found some tentative promise for tDCS to enhance memory, alertness, and the ability to learn new tasks, and to decrease symptoms of anxiety and depression. Anecdotally, users report that tDCS also helps them ease into a flow state (i.e., being “in the zone”), where they can get many tasks done without distraction.
But now researchers are worried that this DIY movement is getting ahead of the science, putting people at risk of burns and poorly understood changes to the brain.
Neurologists think tDCS could be riskier than it seems
Thirty-nine scientists — many of whom study the effects of tDCS — have signed on to a letter published online in the journal Annals of Neurology. In it, they urge the DIY community to be cautious and skeptical.
“While some risks, such as burns to the skin and complications resulting from electrical equipment failures, are well recognized, other problematic issues may not be immediately apparent,” the authors write. “We perceive an ethical obligation to draw the attention of both professionals and DIY users to some of these issues.”
Many of the initial studies on tDCS had small sample sizes, which are prone to producing results that overstate effects or finding an effect in error. One meta study in the journal Brain Stimulation found a net zero effect of tDCS on cognitive functioning, and called for more replication studies of tDCS experiments. Another systematic review found only small physiological effects of tDCS on brain function.
The researchers who signed on to the Annals of Neurology letter aren’t saying there’s no effect of brain zaps. Instead, they’re arguing there’s not yet enough science to support DIY experimentation. And for that reason, DIYers should be a lot more wary of sending currents into their brains.
“I'd say we're most concerned about when people experiment for much longer and much more frequently than we've experimented with,” Michael Fox, a brain stimulation researcher at Harvard and a co-author of the letter, told WBUR.
Here are the main concerns outlines in the letter.
1) There are unknowns about what electricity does to the brain or how deeply it penetrates
Stimulation affects more of the brain than a user may think. Electrodes are often placed in specific scalp locations to target specific brain regions. However, stimulation extends well beyond the regions beneath the electrodes. Current flows between electrodes in complex ways based on different tissues in the head, and can affect the function of various structures along its path. Further, the effects of tDCS can extend beyond brain regions directly affected by the stimulation to connected brain regions and networks. These indirect effects of stimulation on connected brain networks may alter brain functions that are unintended.
2) The effects of stimulation may vary wildly depending on the target brain activity
Stimulation while reading a book, meditating, visually fixating on a point, watching TV, doing arithmetic, sleeping, or playing video games could all cause different changes in the brain. In fact, even activity occurring before tDCS or the time of day tDCS is administered may change the effects of stimulation. Which activity or time of the day is best to achieve a certain change in brain function is not yet known.
3) Enhancing one brain function may hurt another
[B]rain networks interact with each other, such that modifying activity in one network can change the activity in other networks. Therefore, stimulating one brain area may improve the ability to perform one task but hurt the ability to perform another. For example, tDCS can enhance the rate of learning new material, but at the cost of processing learned material, and vice versa, depending on the stimulation site. Such tradeoffs are likely under-recognized as most tDCS studies focus on just one or two tasks. Further, such cognitive trade-offs could develop over time and only become recognizable long after the stimulation.
4) The researchers worry DIYers may try zaps with higher and higher intensities. But there’s no evidence to suggest more is better.
For example, increasing the stimulation amplitude from 1 mA to 2 mA or increasing the duration from 10 min to 20 min might be expected to double the effect, but in fact can actually reverse the effect and cause the opposite change in brain function. More stimulation is not necessarily better; more is simply different.
5) There’s a high amount of individual variability in effects of tDCS that’s not well-understood.
Even across groups of subjects, tDCS effects can be highly variable. Up to 30% of experimental subjects respond with changes in cortical excitability in the opposite direction from other subjects using identical tDCS settings. Even with consistent changes in cortical excitability, these changes can have different effects on individuals’ ability to perform a task.
Overall, it’s important for self-experimenters of any stripe — dieters, fitness buffs, mindfulness trainees, etc. — to know there’s rarely a scientifically validated silver bullet for self-improvement. Evidence-backed insight emerges in fits and starts and often contradicts itself. It takes years for a consensus to emerge, and the consensus is almost always more subtle than initial exploratory studies suggest.
Does tDCS have potential to help people learn and think better? Maybe. But the science isn’t strong enough yet.