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Using tDCS to Reduce Aggression in Inmates

By Celeste Fong

Image courtesy of Pixabay

Earlier this year, a Spanish research team published a pilot study in Neuroscience suggesting that neuromodulation of the brain by transcranial direct current stimulation (tDCS) could reduce aggression in prisoners (Molero-Chamizo et al., 2019). The study was conducted on 41 imprisoned males, consisting of both murderers and non-murderers, who filled out self-report aggression questionnaires before and after undergoing three rounds of tDCS stimulation. The team found lower self-perceived aggression scores after stimulation in the prefrontal cortex. With these results, the team supposedly had approval from the Spanish government, prison officials, and a university ethics committee to move forward with a follow-up study involving at least 12 convicted murderers and other inmates, as well as non-imprisoned volunteers. However, shortly after news of the new study was released, the Spanish Interior Ministry put it on hold. While the reason for this decision has not been said, one can see the worry that such a research proposal may have. Stimulating the brain has always been a controversial topic. Moreover, conducting such work on prison populations poses its own concerns. The potential to shape less aggressive populations could have far reaching societal benefits, but this ultimately raises the question of whether or not a potentially safer world could outweigh the risks present in its research. 

Andrés Molero-Chamizo, the lead researcher of the study, remains optimistic, saying “it could help to keep order inside a prison” (Adam, 2019). Here, his point is clear. The Spanish prison system’s most pressing issue for a number of years has been overcrowding as a result of a lack of staff (Pascual & Aranda, 2016), while the United States is notorious for high incarceration rates (Sawyer & Wagner, 2019). Having less aggressive or violent prisoners could create a better environment for both workers and inmates. Less conflict between inmates, or between inmates and guards, as a result of tDCS, increases security and efficiency, and promotes a method of rehabilitation that could lead to shorter prison sentences (Samuel, 2019). Further, if the stimulation is shown to have a continued positive effect on aggressive tendencies, lower recidivism rates could follow, as former inmates would be less likely to recommit violent crimes (Mooney & Daffern, 2015). Shorter sentences and lower recidivism rates means fewer individuals in the prison system, which prevents overcrowding and allows for an improved quality of care for inmates.  

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Although stimulating prisoners’ brains could produce such substantial benefits, there are a number of ethical concerns regarding this type of experimental research that cannot be ignored. Perhaps the most pertinent of these concerns lies in using prisoners in research. Potential participants must provide their consent, where they decide autonomously, free from influence and coercion, to engage in research. The prison system is an inherently coercive environment where inmates, detained involuntarily and held against their will without the capacity for consent or autonomy, are often persuaded to behave in certain ways in order to receive benefits (including better treatment or reduced sentencing). Inmates can be influenced to participate in potentially dangerous research studies like this one, which involve stimulation of the brain with the intention of altering function, because there is the incentive to develop better behaviors. Showing a desire for rehabilitation, and then demonstrating such rehabilitation, can also increase the chances that an inmate will be given parole, thus reducing his or her sentence length. As a result, it is difficult to create an environment where we can ensure that inmates can authentically decide to participate in this type of research. 

Beyond concerns over the use of vulnerable populations in research studies, other potential worries lie in the use of stimulation itself, particularly as tDCS is intended to alter natural neural functioning by changing cortical excitability through the external application of electrical currents (Nitsche & Paulus, 2000). The question is whether or not an actor who becomes less aggressive through stimulation of the brain is somehow different from one who becomes less aggressive through work done by his or her own accord. This issue is one of identity. As a society, we tend to value self-authenticity as a facet of identity. In other words, we often aim to live a life that is authentic to us, where we can act according to our own values and beliefs to achieve our own goals to become the self we aspire to be. Does the use of stimulation somehow prevent an actor from behaving authentically? And are the resulting efforts of his or her actions somehow discounted as a result of the addition of stimulation? If it is the case that an actor who has the assistance of an external influence like tDCS is no longer able to act authentically, and thus, in a manner consistent with his or her own self-identity, there becomes a serious ethical issue with the use of brains stimulation in prisoners.  

Image courtesy of Pixabay

Given this concern with authenticity, if the aim is to use tDCS on prisoners for rehabilitation purposes, as is the case with Molero-Chamizo’s study, we might wonder if those who became less aggressive with the aid of tDCS could truly be considered rehabilitated. That is, to trust that the effects of stimulation on reducing inmates’ aggressive or violent tendencies are sufficient enough for release from prison into an uncontrolled environment, where they will be allowed to act freely and without supervision. It could be that prisoners who undergo rehabilitation with the aid of stimulation cannot be responsible for their efforts or results in the same way as those who work to achieve their rehabilitation without it. The idea is that stimulation might act as a band-aid where inmates, by virtue of behaving inauthentically, are unable to understand changes in their behaviors as a result of stimulation. Then, for example, rather than learning to better interpret and respond to provoking stimuli, they have a device that has changed their reactions for them with potentially little to no effort on their behalf. In these instances, it might be difficult for them to grasp what is different about their responses in differing circumstances, limiting their ability to adapt to various environments. 

Finally, with regard to methodology, we have yet to determine what it means to be categorized as “non-violent” or “reduced aggression.” It is important to note that the pilot study conducted by Molero-Chamizo and his team tested self-reported aggression using the Buss-Perry Aggression Questionnaire, which asks participants how they relate to particular statements as being more or less characteristic of themselves. This means that aggression scores are indicative of self-interpretation rather than proactive or reactive behavior. Someone who says that they feel less aggressive does not necessarily mean that he or she will be less violent. Therefore, we cannot know if the work done by the pilot study definitively shows that tDCS makes prisoners less aggressive, just that prisoners interpret themselves as being less aggressive or emotionally provoked. 

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If we are to be a society that idealizes a rehabilitative prison system over a punitive one, then the value that tDCS can have towards these efforts is clear. However, we do not yet know how lower self-reported aggression translates to less violent actions. If it is the case that we can stimulate brains to reduce aggression in individuals, we must also acknowledge the portability and versatility of tDCS. For example, it is possible that such technology can be easily used in the home to reduce conflict, or in schools to reduce aggression in students in order to facilitate learning. While these uses are perhaps some years and policies away, it is important to recognize the potential implications that can be brought about by such emerging technologies, and how they might impact our future societies. Therefore, while we cannot discount the benefits that Molero-Chamizo and his team see in their work, it seems that this project will remain inherently controversial. Should this type of research continue, either through this follow-up study or through other means of studies, a bigger question for research ethics will always remain: at what point do potential outcomes of research justify questionable methods? 


Celeste Fong is a current student in the Masters in Bioethics program at Emory University. Having received her Bachelor’s degree in Neuroscience from the University of Alabama at Birmingham, she is interested in exploring how advances in neuroscienceresearch and technology can challenge society’s perception of itself and its values.

  1. Adam, D. (2019, March 06). Exclusive: Brain zap therapy for aggression to be tested on prisoners. Retrieved from 
  2. Molero-Chamizo, A., Martin Riquel, R., Moriana, J. A., Nitsche, M. A., & Rivera-Urbina, G. N. (2019). Bilateral Prefrontal Cortex Anodal tDCS Effects on Self-reported Aggressiveness in Imprisoned Violent Offenders. Neuroscience, 397, 31-40. doi:10.1016/j.neuroscience.2018.11.018
  3. Mooney, J. L., & Daffern, M. (2015). The relationship between aggressive behaviour in prison and violent offending following release. Psychology, Crime & Law, 21(4), 314-329. doi:10.1080/1068316X.2014.989163 
  4. Nitsche, M. A., & Paulus, W. (2000). Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation. J Physiol, 527 Pt 3, 633-639. doi:10.1111/j.1469-7793.2000.t01-1-00633.x 
  5. Pascual, E., & Aranda, M. (2016, December). Prisons in Spain- The penitentiary system. Retrieved from 
  6. Samuel, S. (2019, March 09). A controversial experiment will zap prisoners’ brains to curb aggression. Retrieved from 
  7. Sawyer, W., & Wagner, P. (2019, March 19). Mass Incarceration: The Whole Pie 2019. Retrieved from 

Want to cite this post?

Fong, C. (2019). Using tDCS to Reduce Aggression in Inmates. The Neuroethics Blog. Retrieved on , from


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