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By: Jessika Allen - Real Salt Lake

Is brain doping genius or dangerous?

      Athletes are always looking for ways to improve function in physical and cognitive performance no matter how miniscule that improvement might be1,5. Every year, new techniques, supplements, training philosophies, recovery plans, and technology is developed to help aid these athletes in their goal. Recently, high level athletes, including the Golden State Warriors¹ and the USA Ski and Snowboard Team², have been spotted wearing a new device called the Halo Sport3-7. The device is a headset that uses transcranial direct current stimulation (tDCS) to improve connections in the brain, sharpening mental performance and physical output1-7. Due to its recent development, questions around how the device works, its safety, and its competitive advantage are yet to be answered.   

      Like most new technology, the idea behind the Halo Sport, tDCS, comes from a diverse and interesting history1,8.  It started with the Egyptians studying catfish8. We do not know how they used the catfish, but they knew the catfish had some electrical properties8. Later, there is evidence that the torpedo fish was studied by scientists from the time of Plato through the time of the Roman empire8. They found the fish to have electrical properties that could be used to generate numbing effects and help with headaches8. In the 11th century, the electric catfish reappeared and was used by Ibn-Sidah to treat epilepsy1,8. TDCS gained further popularity when direct current was used during the beginnings of electrophysiology8.  Since these unrefined forms of tDCS, the technology has continued to evolve into its core today of a device with electrodes that produces a current while touching the scalp, causing changes in the brain8 

      The definition for transcranial direct current stimulation is when a weak direct current (DC), typically two to three milliamps, is run through the scalp via placement of electrodes, with a ramp up and ramp down period and the goal of creating change in one or both cortexes1,3,5, 6,8-23. At this point in time, scientists have shown that tDCS influences the brain; however, they have not discovered the exact reason this occurs14,16,23,24, especially in athletes6, though several theories exist8. One theory involves positive and negative stimulation. The Anodal (positive) stimulation is thought to set off the excitatory neurons and improve cortical excitability by increasing their resting membrane potential, while at the same time lowering the resting membrane potential for the inhibitory neurons in the same area1. The opposite effect occurs for the cathodal (negative) stimulation which decreases cortical excitability9. Similarly, another study mentions tDCS affecting neuronal firing rate and patterns along with synaptic release probability, uptake, and sensitivity10. These changes, potentially caused by one of the previous two mechanisms, are thought to alter the function of the target area and increase short-term neural plasticity which leads to short learning times and improved long-term learning. (a real-world investigation) The main areas tDCS is used over are the primary motor cortex (M1) to improve motor learning and the dorsolateral prefrontal cortex (DLPFC) to improve memory and cognitive function9.   

      A major concern of any new medical device is its safety, especially when that device’s purpose involves brain modulation. Overall, the research indicates that tDCS has an excellent safety record in a laboratory setting during short term use1,4,11,18,24. Side effects that have occurred are typically mild and can include sensations of burning or pain24, fatigue, headaches4,9,24, and skin redness12,24. Less likely but still a concern is nausea, mood changes, and seizures9. MRI studies have not yet shown tDCS to generate brain edema or alterations in the blood brain barrier or cerebral tissue9,12. Since tDCS uses a weak direct current of two to three milliamps, there is concern for electrical damage to the brain. However, several studies in rats have gone to the threshold of damage and then been scaled to estimate the rates required to negatively impact a human. The predicted human damage threshold ranges from 67 to 173 milliamps, far greater than the current used by the Halo Sport device12,24. There have also been several studies in rats, mice, and post-stroke humans that have demonstrated a probable neuro-protective effect from tDCS without any major negative events. Thus, it appears that tDCS can be safe to use in these populations12. Humans are all made differently3, and, although current models and experiments have not found head size and resulting current density to have a major effect on subjects12, it is still an area that could use further research. Although there have been numerous studies on short-term tDCS, there are minimal studies of the effects of daily long-term use2,11,12,24. The few cases where patients, with medical diagnoses, have used tDCS for over 100 visits have not shown adverse events despite extensive cumulative exposure12. However, prolonged exposure and cumulative effects have not been widely studied in a healthy population12.  Lastly, there are no set protocols for tDCS2. Current research protocols vary in the amount of current used, overall time the electrodes are left on, how many sessions occur, and required changes with the different placements of the electrodes2. Despite the lack of protocols, most studies have demonstrated no severe adverse events12. Overall, the research suggests that tDCS can be used safely with no evidence for irreversible injury; however, further research is needed to determine long-term cumulative effects, best protocol practice, and safety in all populations.  

      The main component that sets athletes apart from the general population is their physicality and skills. Nevertheless, at a certain level, everyone is physical gifted, and athletes must find something extra that allows them to make marginal improvements compared to their opponents11. Fatigue6, for example, is a major factor that can limit an athlete’s performance. Muscle fatigue can occur when the M1 fails to produce significant output in combination with decreased output from the peripheral muscles13,14.  Through use of tDCS, the M1 can be stimulated to delay fatigue1,6,11 and decrease perceived exertion2,11,13. This increase in time to exhaustion has been demonstrated in cyclists (anodal cathode was placed over the occipital cortex) at a continuous 80% peak force load14,15 and in runners at an 80% intensity13. Another study done in cyclists demonstrated improved peak power17, decreased heart rate, and decreased perception of effort at submaximal workloads when the anodal cathode was placed over the Left Temporal Cortex (T3) 11,14,15,16. In golfers, tDCS has been shown to help improve putting accuracy compared to the sham group and have greater carry over effects6. In weightlifting, a two to three percent weekly gain (compared to less than one percent in the sham group) in maximum output was found when tDCS was used at the beginning of a workout and the anode was placed at Cz (per 10-20 system) with the cathode placed on the shoulder6. Through use of the stimulation, athletes who had hit plateaus in training thought they were able to get past them more easily and demonstrated via coach feedback that they had made and retained gains6. Finally, though tDCS’s stimulation it primes the neurons in the brain getting them ready to communicate with your muscles faster1,2,5,6,17. When used by the U.S. Ski team to practice jumping, the Halo Sport improved their jump coordination by 80% compared to the sham group2. 

      While physical training is the focus for athletes, mental performance is also a key component17 that separates the good from the great. When the anode was placed over the left DLPFC during cycling, athletes exhibited improved cognitive performance and mood elevation,11,15. When stimulation is placed over the DLPFC, studies have demonstrated long-term improvements in memory and cognitive function leading to improved motor learning9. Moreover, after tDCS stimulation, scores on the Beck Depression Inventory decreased by 4.5 points7. Gains of 5 to 20 percentile ranks have been shown in athletes alternated, divided, and sustained attention along with recognition memory7. Since athletes are constantly expected to perform at such a high level and are more likely to deal with depression1 due to this, tDCS could be a valuable tool in helping athletes through these mental challenges along with the noted physical benefits7 

      Research involving tDCS for athletic performance has mainly consisted of single groups of muscle with the occasional small study diving into functional testing2,3,18-21. TDCS devices such as the Halo sport have begun to show up at the professional level in various teams,11,15.  These teams have all used tDCS but with unknown application,11,15. With this new technology becoming more popular but with limited in-depth sports-specific research supporting it, sports authorities should start determining if brain doping through tDCS fits into the current supplementation framework or if it provides an unfair advantage,11,15. 


Jessika Volz PT, DPT, ATC, FAAOMPT 

Assistant Athletic Trainer and Physical Therapist 

Real Salt Lake 



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