Transcranial Direct Current Stimulation: Cognitive Benefits, Limits, Ethical Concerns and Future Usage

Abstract Transcranial Direct Current Stimulation (tDCS) has become a popular tool for treating illness and pain, as well as for cognitive enhancement. Although tDCS has been found to be affective, it is still important to evaluate safety and ethical concerns. In this paper I present studies using tDCS. I also evaluate the ethical implications of tDCS, especially for the use of brain stimulation on healthy people.

Introduction Transcranial Direct Current Stimulation, also known as tDCS, is a form of non-invasive brain stimulation. Trials using tDCS began around the 1950s for treating depression, but it faded as a technique since most of the results were mixed (Dockery, Hueckel-Weng, Birbaumer, & Plewnia, 2009, p.17). Research with tDCS has become more popular recently, therefore it is important to understand what tDCS does, how it affects the brain, and what the ethical concerns are. TDCS has a wide cognitive scope, but it faces limits. TDCS is safe and has many applications such as to enhance learning and memory, to reduce pain, as well as to treat various mental illnesses like depression and schizophrenia. TDCS clinical studies vary as far as organization, but there is a similar structure and schedule to applying stimulation. An anode and cathode are placed on the body. The anode has a positive polarity, it is placed on the region of the brain that is being targeted for a specific task

(Parasuraman & McKinley, 2014, p. 2). The cathode has a negative polarity, it is placed over a region of the brain that a researcher is seeking to depress. In order to test how effective tDCS is in a trial the researchers should have a control group. The control groups are referred to as the sham groups, sham, in this case, means placebo. The participants in the sham group do not actually receive active stimulation. The sham group’s results will be compared to 1mA, 2mA, or both levels of stimulation (Hoy, Emonson, Arnold, Thomson, Daskalakis, & Fitzgerald, 2013, p. 1778). The procedure will include multiple sessions of tDCS spread out over a few days or weeks. Additionally, the reason tDCS works is because by exciting neurons, tDCS increases neural plasticity, which means that neural connections can change (Coffman, Trumbo, Flores, Garcia, van der Merwe, Wassermann, & ...Clark, 2012, p. 1600). Non-invasive brain stimulation has become a popular research tool for depression, pain, schizophrenia, learning and memory. TDCS is valuable for improving the quality of life of people who are resistant to medication. It is not the case that everyone responds the same to medication. For those who are resistant, tDCS is an alternative that can be used and it can be paired with existing treatments (Brunoni, Boggio, De Raedt, Bensenor, Lotufo, Namur, &…Vanderhasselt, 2014, p. 47). Another important use of tDCS is for cognitive enhancement. Since tDCS can benefit the lives of people who are ill, then it could be the case that it can be used on healthy people to improve cognitive functions, even when there are no existing functional issues. Studies exist evaluating the effect of tDCS on healthy subjects, these include the effect on working memory, learning, and problem solving. If it is the case that brain stimulation can improve the cognitive functions of healthy people, then it could be used by anyone for anything they want to improve on. For example, if Jim is bad at sports, he may be

able to use tDCS on his motor cortex to improve his motor coordination. The use of tDCS on healthy people raises ethical concerns that I will evaluated. I claim that tDCS has a wide cognitive scope, but it faces limits and ethical problems. TDCS has been regarded as a safe form of non-invasive brain stimulation that has many applications. In order for tDCS to be used more often both as a treatment for illness and as a cognitive enhancement, the ethical concerns should be addressed and the mixed results from various studies should be significantly reduced. In this paper I will present studies in which tDCS is effective, as well as cases in which it is not. I will also present the ethical concerns that have been raised in order to have a more critical view of tDCS, and I will respond to these critiques. After this evaluation I will conclude with describing what a future with more tDCS looks like.

Discussing the Safety of tDCS First, it is critical to understand that across tDCS trials, the side effects have been mild and non-life threatening. In a meta-analysis of tDCS research, Brunoni and colleagues evaluated the side effects of tDCS. The researchers found that the most common side effects were itching and tingling sensations (Brunoni, A., Amadera, J., Berbel, B., Volz, M., Rizzerio, B., & Fregni, 2011, p. 1136). Additional side effects included headaches, and slight burning sensations. Fatigue was also reported as a common effect, but this could be related to the duration of the study being conducted (Antal, Boros, Paulus & Poreisz, 2007, p. 213).In the analysis, the researchers discovered that there may actually be a lack of proper reporting of side effects, so in order to obtain a clear view of side effects of stimulation, more monitoring must be done and subjects in studies should fill out questionnaires about their experiences (Brunoni, et

al., 2011, p. 1143). When the side effects are properly reported within each study, people will be more likely to accept the results, as well as accept tDCS as a safe form of non-invasive brain stimulation. Although the most common side effects are mild and not lasting, the most severe side effect discovered after stimulation with tDCS is skin lesions (Pascual-Leone, Rodriguez-Eloy Opisso, & Soler, 2014, p. 386). Fortunately, the skin lesions are small, none of them more than a couple centimeters, and they are not painfully formed during stimulation. Even though skin lesions have developed, they are not common and there are simple ways to avoid them. In order to reduce the formation of skin lesions, Pascual-Leone and colleagues propose specific rules for using electrode. The electrodes should be plastic and used with an electrode cream in order to lessen how much the electrodes directly touch skin (Pascual-Leone, et al., 2014, p. 387). Skin lesions should not, and does not, deter us from using tDCS on people. Side effects for medication for depression include suicidal thoughts, gastrointestinal problems, nausea, anxiety, and insomnia. Comparing the side effects for the treatments of medication and tDCS would lead most people to say that the side effects for tDCS are less harmful. If tDCS is effective, then it would be better to use it as a treatment, rather than using a lot of medication that could cause more severe side effects.

The Effect of tDCS on Mental Illness Mental health is a prominent topic in society today. Many people suffer with issues ranging from minor anxiety, to major depressive disorder and schizophrenia. All of these contribute to lowering the quality of life of an individual. With depression alone, it takes a few

months in order to get the dose of medication correct for an individual in order to start reducing depressive symptoms. Unfortunately for some people, medication does not always work. Some medication can cause more suicidal thoughts and feelings. In this section I will introduce studies that use tDCS to treat mental illness. These cases are important since if tDCS is effective, then it can be paired with cognitive treatment, rather than medication and cognitive treatment, to better reduce symptoms and bring a higher quality of life back to people struggling with mental illness. I believe the most relevant study on the influence of tDCS on depression is “Cognitive Control Therapy and Transcranial Direct Current Stimulation for Depression: A Randomized, Double-Blinded, Controlled Trial.” In this 4 week trial, the participants received tDCS on the dorsolateral prefrontal cortex (DLPFC) combined with cognitive control therapy (Brunoni, et al., 2014, p. 44). Assessments indicated that the combined therapy helped improve symptoms, especially when the participants were older. The researchers discussed that the reasons for this could be that older adults already have a higher capability to learn faster and benefit more from this treatment (Brunoni, et al., 2014, p. 48). Unfortunately, it is important to keep in mind that tDCS is not always effective. “In Treatement of Depression with Transcranial Direct Current Stimulation (tDCS): A Review,” Nitsche and colleagues highlighted that replications of studies using tDCS to treat depression are not always successful (Nitsche, Boggio, Fregni, Pascual-Leone, 2009, p. 16). The researchers attribute this result to differences in severity of depression in individuals. Some people may be more resistant to treatment because they are in a deeper state of depression. They note that it is not clear which specific areas of the prefrontal cortex influences the effects of tDCS, so there is still more to be known. This is something to keep in mind when people seek treatment for depression.

TDCS can help people diagnosed with schizophrenia who have problems with everyday cognitive function be better able to complete cognitive tasks (Hoy, Arnold, Emonson, Daskalakis, & Fitzgerald, 2014, p. 99). In one study, participants received tDCS on the DLPFC, either 1mA or 2maA, then completed a working memory task. 2mA of stimulation improved performance on the task, whereas sham stimulation did not. This shows that tDCS can help improve functions of those diagnosed with schizophrenia, which would certainly improve their quality of life. TDCS has been effective for treating depression and schizophrenia, but it does not treat all kinds of mental illness. In a study conducted evaluating the effect of tDCS on cigarette craving, when tDCS was applied to the DLPFC, it did not reduce cigarette craving of people who were trying to quit smoking (Xu, Fregni, Brody, & Rahman, 2013, p. 4). This indicates that tDCS cannot be used as an ultimate treatment for mental illnesses. TDCS needs to be tested for each individual illness before it is accepted as a treatment. Although it has been shown that tDCS can be a treatment for mental illness, it is still critical that patients receive cognitive therapy with their stimulation therapy. TDCS can be effective in reducing depressive symptoms, but those who suffer with depression need to know how to manage their thoughts and behaviors cognitively as well. In the future this will allow them to have the techniques to combat their illness before getting stimulation or medication that alters their brain function. This applies to people diagnosed with schizophrenia and any other illnesses that may be found that can be treated with tDCS.

TDCS as a Treatment for Physical Problems We want to use tDCS to treat physical pain as well because some people are resistant to pain medication. There is a limit to how much medication a person can take, and having to be in pain constantly can be unbearable. Having another treatment that is safe and easy could be the simplest solution to reducing the amount of pain a person has. I believe that if someone has extreme long-lasting pain, that tDCS should be used to treat it. TDCS has been used to treat chronic pelvic pain. In “A preliminary Study of Transcranial Direct Current Stimulation for the Treatment of Refractory Chronic Pelvic Pain,” researchers explained that “chronic pelvic pain is related to a dysfunction in pain-related neural networks, including the limbic system…At the central level, pain leads to plastic changes in an extensive neural network that includes the spinal dorsal horn, limbic system, and cortical structures such as the somatosensory and prefrontal cortex (Fenton, Palmieri, Boggio, Fanning, & Fregni, 2009, p. 104).” These researchers hypothesized that using tDCS could help reverse the changes in plasticity, to reduce the amount of pain being experienced. The stimulation was directed at the motor cortex, and there was a 2 day treatment. After 2 weeks the subjects reported having less symptoms of their pelvic pain (Fenton, et al., 2009, p. 106). TDCS can also help treat pain for people who have had spinal cord injuries. In one study, tDCS was applied to the motor cortex, much like it was during the pelvic pain experiment, and treatment lasted for 3 weeks (Fregni, Boggio, Lima, Ferreira, Wagner, Rigonatti, & Castro, 2006, p. 198). The treatment significantly reduced pain for at least 24 hours, and no adverse side effects were reported (Fregni, et al., 2006, p. 203).

Visuospatial neglect typically occurs after stroke in some people, and results in an inability to process information on one side of their visual space. One study evaluated the effect of tDCS on a man who has visuospatial neglect. In this single-case study, the patient received regular therapy for this disorder, as well as biparietal tDCS (Brem, Unterburger, Speight & Jäncke 2014, p. 2). The measure in this study was attention on the side of the hemisphere that was damaged. TDCS improved attention and alertness, even after one session of tDCS (Brem, et al., 2014, p. 7). Although this is a promising treatment for visuospatial neglect, the study does not have much external validity since it was a single-case study. A common problem that people face post-stroke is a deficiency in hand movement capabilities. Applying tDCS to the motor cortex can help improve motor function (Hummel, Celnik, Giraux, Floel, Wu, Gerloff, & Cohen, 2005, p. 497). While completing a hand movement task, like picking up small objects, participants in a study were given stimulation, and the results indicated that those in the stimulation group had improved hand capabilities, but after being tested 10 days later the results were no longer significant (Hummel, et al., 2005, p. 496). This indicates that tDCS can help, but it may need to be given on a regular basis, since the damage is so strong. Research has also supported tDCS being safe for stroke patients. Rossi and colleagues studied change in autonomic functions in stroke patients who receive stimulation. They found that there were no side effects from the tDCS procedure (Rossi, Sallustio, Di Legge, Stanzione & Koch, 2013, p. 203). They did not find that it improved their ranking on a national stroke scale, however. These results tell us that tDCS is safe, but that stimulation alone does not produce effects on people who have had strokes, but when it is paired with tasks and used in different brain locations it can help hand function which is a significant benefit.

These results indicate that tDCS can treat a variety of physical problems. These studies are structured around very serious conditions, like lasting pain and functional issues, but I believe that tDCS could be used to treat recovery for people who need physical therapy for muscle damage. If someone needs physical therapy, tDCS could be combined with it in order to speed the recovery process. Overall, the benefit of tDCS being affective is that it continues to be a way to improve the quality of life for people who could be struggling with mental and physical problems. The Use of tDCS on Healthy People – Improve learning and memory TDCS can enhance cognitive functions for people who physically or mentally ill, so now it is time to wonder how tDCS can help healthy people, as well as question why we should even want to use it on healthy people. There are many ways to enhance our bodies. People exercise, do yoga, and change their diets all to make themselves capable of doing more and living more. Since we do so much to enhance ourselves physically, then we should be able to enhance our cognition as well. People already do things like this, there are apps that allow you to do “brain exercises,” and some people meditate which allows them to have more control over their thoughts. A healthy person may find tDCS attractive because it can help him/her learn faster and have a better memory. New skills that people find difficult can be made easier by a few sessions of tDCS. Although this kind of cognitive enhancement seems desirable, there are many ethical concerns that have come about from this discussion that need to be addressed. Before discussing these, I will give examples of tDCS working as a form of cognitive enhancement, and explain what it can and cannot do for us. Learning is one of the most important cognitive capabilities that we have. All of our lives we spend learning new things. The whole first quarter of our lives is dedicated to learning

in schools. TDCS enhances learning ability, which has many benefits. In a study based on target detection tasks, researchers discuss how simple target detection is a desirable skill to have, since it can lead to our survival (Coffman, et al., 2012, p. 1594). This is especially important for people in the military, but even in regular society there are bomb threats, school shootings, and health crisis. Identifying these threats could be life-saving. In this study, participants scanned images to search for threats, including snipers and bombers, which were hidden in various locations. The goal of the study was to apply tDCS during a training period to see if tDCS influenced the ability of people to notice threats faster and more accurately. There was a significant effect. The researchers indicated that participants were better at detecting targets after training, than when the images were new (Coffman, et al., 2012, p. 1600). This means that when you have practice with something, tDCS is more influential than when you are doing something completely new. Additional support for tDCS influencing learning is another study conducted by Kineses and colleagues (Kineses, Antal, Nitsche, Bartfai & Paulus, 2003, p. 116). In their study, the task required people to make predictions based on specific combinations of geometric forms, each corresponding to particular weather outcomes. The researchers discovered that anodal, rather than cathodal, stimulation improved learning during probability tasks. A guideline that can be created from these results is that we should always practice something before introducing tDCS, and this will lead to more improvement in mastering a skill. Another skill that is used in everyday life is planning. Planning gives us the advantage of being able to look ahead and make decisions based on present and future states. In one study, tDCS was applied to participants that were solving planning tasks (Dockery, et al., 2009, p. 7272). One of the most significant aspects of this study was that the researchers had a different

protocol for tDCS application than other studies. They indicated that cathodal tDCS was applied during the learning phase, which they say is important because cathodal stimulation causes the area of the brain it is on to suppress (Dockery, et al., p. 7275). Anodal stimulation was applied after learning occurred, which enhanced the participant’s ability to perform the task. This tells us that the way tDCS is applied is critical to the enhancement of cognitive functions. Not only should researchers focus on stimulating particular areas of the brain to increase plasticity, but they should also know that cathodal stimulation is important in getting people to focus on a task. Additionally working memory, more specifically reaction time to a task, was improved by tDCS (Daskalakis, Fitzgerald, Hoy, Teo, 2011, p. 2). The strength of tDCS was evaluated to see if 1 mA or 2 mA would influence working memory differently. The strength of the current had no effect, but there was overall improvement with stimulation. Unfortunately this is not highly supported, since in another working memory task, it appeared that tDCS slowed the reaction time of participants (Born, Marshall, Matthias, Siebner, 2005, p. 4). More studies will need to be conducted to determine if working memory can be enhanced with tDCS, and which brain locations should be activated. We know more about what tDCS can do, but what it cannot do is also critical to understand. Though tDCS has improved depressive symptoms, for healthy people it does not change mood either negatively or positively (Plazier, Joos, Vanneste, Ost, & De Ridder, 2012, p. 459). So on a bad day, or before a test when someone is feeling down, tDCS is not a simple solution for mood changes. Additionally, tDCS does not change some autonomic functions, such as body temperature and cortisol level (Raimundo, Uribe, & Brasil-Neto, 2012, p. 198). It does, however, change skin temperature, but this does not concern us since it makes sense that applying stimulation would cause our skin to be slightly heated.

Are the Effects of TDCS Long-Lasting? It appears that tDCS is effective as a clinical treatment, and it could possibly be used for cognitive enhancement. One of the most prominent questions that should be raised is how much stimulation is necessary, as well as how long do the effects last. Each trial has their own schedule for stimulation, but many of them have either daily sessions of tDCS, or weekly sessions. In the target detection tasks, the participants had to wait one hour before the tests occurred (Coffman, et al., 2012, p. 1595). In other tasks, such as the cognitive control therapy study, the evaluation occurred two weeks after the treatment had stopped (Brunoni, et al., 2014, p. 44). Additionally, the treatment for visuospatial neglect had an assessment given 3 months after the end of treatment (Brem, et al., 2014, p. 2). Unfortunately, none of the studies evaluated for this paper were longitudinal, the longest time between treatment and evaluation is only a few months. In order to have a more clear view of the effects of tDCS, we need to know how long the effects can possibly last, since that will inform us about how many times tDCS is necessary.

Should Healthy People use tDCS? TDCS can improve some cognitive functions, but’ tDCS used as a cognitive enhancement raises some troubling ethical concerns. In An Ethical Discussion of the Use of Transcranial Direct Current Stimulation for Cognitive Enhancement in Healthy Individuals: A Fictional Case Study,” the idea of a “Brain Boosting” tDCS clinic is introduced (Lapenta, Valasek, Brunoni, & Boggio, 2014, p. 176). This clinic gives healthy people the opportunity to use tDCS as cognitive enhancement. One of the concerns raise from this discussion is if tDCS gives some people an unfair advantage than others (Lapenta, et al., 2014, p. 177). My response to

this concern is, as stated earlier, many people have opportunities to enhance their bodies. In a track race, one person may have their own person track that they can practice races on, while another does not have this. When they run the race, no one wonders if the person with their own track was cheating. Also, if you have access to notecards, which help you study, no one says that is cheating, even though other people may not have access to notecards. TDCS should not concern us as a form of cheating. Some more common concerns include that there is no specific training for someone who wants to apply tDCS to people (Cohen Kadosh, Levy, O'Shea, Shea, & Savulescu, 2012, p. R109). In fact, people are applying tDCS to themselves in their own homes which could be very dangerous without specific knowledge of neuroscience and psychology. The researchers in tDCS studies tend to be neuropsychologists who understand the brain very well. The reason knowing the brain is important is because if someone is seeking to enhance their motor function, but puts the electrodes on the prefrontal cortex, this will not change their motor capabilities. It’s possible that someone may apply too much stimulation since they are not seeing any results, which could result in brain damage. Researchers only apply stimulation for about 20 minutes and over a period of time. These guidelines should always be followed. People should be trained to apply tDCS in order to avoid any possible brain damage that could occur.

The effect of tDCS on Cognitive Development Since tDCS has improve learning ability, it would seem favorable for children to receive tDCS in schools in order to get the most out of their education as possible and to increase their chances of getting a good job in the future. Children go through cognitive

development at various ages, so this makes cognitive enhancement used on children controversial. In trying to enhance one function like language, there may be a detriment in other developments such as facial recognition (Cohen Kadosh, et al., 2012, p. R109). We do not know how the enhancement of one area changes the function of another aspect of cognition, since studies with tDCS are specific and focus on one level of cognition like learning or memory. Without knowing this, we cannot know all of the side effects of tDCS, so we should certainly not use tDCS on a developing mind. Additionally, if there was a side effect that was unexpected, there would be many questions about who would be responsible. It could be the responsibility of the person who applied tDCS, or it could be the parent for allowing a child to have brain stimulation. Another issue that arises from the idea of tDCS being used on children is that it appears that tDCS works more for older adults than those who are younger (Brunoni, et al., 2014, p. 47). This could be because the older people become the more neural connections there are, which can be changed. It is possible that tDCS would not work on children because they have not yet formed the cognitive skills to do certain tasks. The only answer right now to these problems is that tDCS should not be used on children. Once more is known about neural mechanisms and the influence tDCS has on it, then these questions could be considered. TDCS and Autonomy/Identity Autonomy is the ability for people to make uninfluenced decisions. If tDCS changes our cognitive functions, then it could be the case that decisions could not be autonomous. For example, in the military, professionals make critical choices about the lives of other people. In “Why Non-Invasive Brain Stimulation Should Not be Used in Military and Security Services,” the difference between clinical studies and real life are made (Sehm & Ragert, 2013, p. 1).

Clinical studies evaluate and monitor specific cognitive functions, but the decisions and processes made in real life are much different than those in scientific studies. The authors argue that it is not safe to allow military professionals to partake in brain stimulation, because there is no way to know right now how tDCS influences people outside of the lab. It is possible that tDCS has an effect on autonomy, but another question that comes about from this ethical discussion is whether tDCS influences identity. There is debate about what identity is. Some extremists believe that we are not the same person as we were as a child, since our bodies are not the same. In this view, tDCS would change identity since it changes neural plasticity. Most people would argue that even though we do not look the same or may have new skills, we are still the same person. One reasonable criteria of having the same identity is having a memory of past events. Given this notion of identity, tDCS does not change who we are, it only enhances what we have. TDCS does not reduce our ability to have memories, it actually makes our capabilities for memory stronger. Overall, we do not have to worry about tDCS changing identity.

Conclusion In conclusion, tDCS is a safe form of non-invasive brain stimulation that has a wide cognitive scope. The benefit of tDCS becoming more popular is that it can be another alternative for people who have mental or physical illness and need more than the help medication is giving them. TDCS treatment should always be paired with cognitive treatment to continue to give people the skills to work on their issues before seeking treatment and during treatment. In the future, researchers will attempt to treat other illnesses with tDCS and be more focused on the

possibilities of cognitive enhancement. This option could possibly make the quality of life for an individual better, and that is the most significant benefit of all.

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