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Would you approve if someone asked you to place electrodes on your skull and apply current to your brain, in order to improve your focus or get rid of your depression? While you may think twice before allowing such an action, many people have preceded you, and their reactions are very enthusiastic.
“My brain feels immensely efficient at sorting incoming data and sensing information. I have also experienced deep states of calm introspection.” – “I am having the best sleep I have ever had consistently. I have an experience of alertness that far surpasses anything else I have ever seen.” – “I second-guess myself less and adapt more quickly. I make decisions more easily, with less fear, uncertainty and doubt.” – “I have been able to rein in my anxiety and thereby my anger and depression too.”
Reading this, it would not be surprising if these were reviews of a medicine like Ritalin or another stimulant or drug. However, these are reviews found on a website www.thebrainstimulator.net selling tDCS devices: devices with electrodes to be placed on your skull that apply current to your brain. What is tDCS, and what do we know about its risks and long term effects?
TDCS, which is the abbreviation of transcranial direct current stimulation, is a form of neurostimulation. Where other cranial electrotherapies mostly use alternating current, tDCS uses a weak, constant current. This current either depolarizes or hyperpolarizes the electric potential in the membrane of neurons, causing respectively more or less spontaneous cell firing. By varying the position of the electrodes and the power used, one could stimulate or depress a variety of neurological phenomena. Originally, scientists developed tDCS with the aim to help patients suffering from brain injuries, depressions or diseases like Parkinson or Alzheimer. However, a lot of reports have been published on other possible effects of tDCS, making it more and more popular for the healthy public. Although the studies are not considered convincing or even reliable by everyone, there are results stating that tDCS could improve learning and numerical reasoning, increase working memory and pain threshold, and decrease anxiety and depression.
The question that arose from these results is how reliable the studies were. When an adolescent explains on YouTube https://www.youtube.com/watch?v=X8PFqNTcrdA how he felt “really angry and depressed” when he placed the electrodes on certain locations on his skull, it seems obvious that his conclusion that he “guessed that was not a good idea”, is neither scientific or reliable. But what about the numerous reports that have been published on research on tDCS? How can we be sure that the effects of tDCS are really as noticeable and effective as they are said to be? Australian neuroscientist Jared Horvath did not trust all extremely positive research results, and decided to do a meta-analysis http://www.sciencedirect.com/science/article/pii/S0028393214004394 of all hundreds of studies that claimed to have found an impact on cognitive and behavioural activities. From this group of studies, Horvath first discarded all studies that were done without a control group. Furthermore, he excluded results that were only stated by one study, and therefore had never been replicated by any other researchers. After this, Horvath started analysing and comparing the results of the remaining 200+ studies.
The two main conclusions that Horvath draws from his meta-analysis are that the findings of studies investigating the same phenomenon differ highly, and that the differences in effects on individual participants can be such opposites that they outweigh each other. Regarding the first conclusion, Horvath explains that several studies on the effect of tDCS on working memory all come up with different conclusions and results. It seems sure that tDCS has some effect on working memory, but what the exact effect is, is unclear. Furthermore, many studies use rather small sample sizes, sometimes not even more than fifteen to twenty participants. Hence, as Horvath states, when one of these participants encounters a certain effect, it cannot be determined whether this effect is a common result, a placebo effect or an anomaly.
Roi Cohen Kadosh, a researcher at the University of Oxford, did research elaborating on Horvath’s other conclusion: the effect on the result of individual differences between participants under the same tDCS treatment. Kadosh published a research http://www.jneurosci.org/content/34/50/16605.shorthttp://www.jneurosci.org/content/34/50/16605.short on the effect of tDCS stimulation on participants who were either anxious or confident about their numerical reasoning and mathematical skills. It turned out that the nervous group experienced a positive effect of the tDCS with reduced reaction time and levels of stress. The more confident group, however, had an opposite experience where their reaction time increased. In this experiment, the participant were separated based on their confidence in their mathematical abilities. Imagine what would happen is this exact same group of participants was used in an experiment that does not differentiate on this feature. In that case, the individual results of an tDCS session would be highly different and even opposite, and would outweigh each other in the average result. These individual results would then outweigh each other in the average result of the effect of the tDCS session, such that it could be concluded that the session did not have any effect at all. According to Kadosh, such individual differences might also be misinterpreted in a study because of the setup of the group of participants. “It is highly likely that the research groups are sampling their participants from a similar environment and therefore reducing the impact of individual differences”, so Kadosh states. Not only confidence in abilities, but also gender, age, medications, both physical and mental health and even being right- or left-handed can influence the individual outcome of a tDCS session.
Besides the dissension on the positive effects of tDCS, there is a lot of uncertainty about the negative effects of it, especially in the long term. What is most scary to researchers on this subject, is the growing popularity of DIY (do it yourself) tDCS devices. On YouTube and on the Reddit community of tDCS, there are plenty of tutorials on how to make the electrodes by yourself. Considering that most online bought devices can cost over 100 USD, it is not surprising that a homemade device costing only about 10 USD for the components, like a 9 Volt battery and two sponges, is attractive. However, the downside of this is that people start experimenting with the current and the positions of the electrodes themselves, without proper information or guidelines except for the shared experiences of other users on social media. This gives situations where someone asks the Reddit community https://www.reddit.com/r/tDCS/comments/7fq22d/help_please/ for help when her 20 minute sessions twice a day only have negative effects on her depression, or where a YouTube commenter tips the aforementioned angry and depressed adolescent that he might try to switch the anode and cathode, to apply the current in reverse direction. Of course, all these advices are well-intended, but is it really safe to electrify your brain with so little and unprofessional background information?
This was exactly what 39 researchers from Harvard Medical School, the University of Pennsylvania and other universities and research communities doubted. This drove them to write an open letter http://www.tmslab.org/publications/595.pdf , warning all users of (homemade) tDCS devices of the risks they are facing. The main message of the researchers is that there is a lot that is yet unknown. For example, the effect of targeting a certain part of the brain to the surrounding parts has not yet been found. Furthermore, there are no studies yet where tDCS is applied as frequently as some home-users do. Taking in consideration the individual reactions and the effects of little changes in the current’s amplitude or session duration as well, the total effect of tDCS for home-users is very unpredictable and hence considered highly risky. In addition, the researchers discourage the use of tDCS on children, considering that their brain is not yet fully developed and hence possible damages can have even worse, and longer lasting, effects. For online bought tDCS devices, the same risks hold, although there might be some protection such as pre-installed limits on, for example, the currents’ amplitude. However, producers are not obligated to implement such limits, since tDCS is not yet approved as a medical device by the United States Food and Drug Administration (FDA), although they are planning to do so. Hence, tDCS devices are not yet under control and regulation of this federal agency yet, giving producers more freedom in the way they design their product.
Given all risks and uncertainties of tDCS, it does not seem very attractive to place electrodes somewhere on your skull, especially with some homemade, 10 USD device. On the other hand, reading all excitingly positive reactions on social media, it must be in some way pleasant to electrify your own brain. However, no matter how enthusiastic you may be, keep in mind the powerful lesson given by most researchers on this topic: do not try this at home. And furthermore, an electrode may give you alertness and a positive feeling just as a cup of coffee can do, but real health and happiness will take more than some wires, batteries and sponges.
This article is written by Marleen Schumacher