Written by Ana Sousa and Daniel Ribeiro
A study looking at the use of tRNS, a non-invasive brain stimulation technique that is being used to manipulate motor function
How cool would it be to be able to move someone else’s hand? Perhaps we could make our friends do some tasks for us. Or we could make kids finally clean their rooms. Although making children focus on housework or homework might be truly rocket science, making someone do a basic hand movement is not so much.
Scientists have been doing this by passing an electrical current through someone’s skull. Does this sound scary? To be clear here, it is not like giving electrical shocks to someone. There is no need to fear it, as it is a common and non-invasive procedure that goes by the name of Transcranial Electrical Stimulation. This is a group of techniques that have been studied in the past years by scientists. One of these techniques has been used to study the region of the brain responsible for the movement of the human body – the motor cortex.
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A recent paper published last month in the Scientific Reports of Nature Research shed some light on the parameters of the Transcranial Random Noise Stimulation (tRNS) technique (1). Regardless of its long, complicated name, tRNS is promising in the investigation of motor, sensory and cognitive tasks. It has been used successfully to improve visual detection or discrimination (2-3) and can improve the perception of facial identity (4).
This method may be effective in the reduction of pain in multiple sclerosis (4) as well as reducing depressive symptoms (5) and being effective in other diseases such as schizophrenia and Parkinson’s disease (6-7). Despite these results and the growing acceptance in the scientific community, the way tRNS operates is still a bit mysterious. Research has been focused on the role of tRNS in cognitive functions (1) but this time the published paper studied one stimulation parameter that might be the key to refine it: the high-frequency band.
To understand this basic parameter, one must wonder how the overall technique work. It was first applied in humans in 2008 by Turney et al from Göttingen University (8). The difference between tRNS and other electrical stimulation techniques is that the electrical current runs in random alternating frequencies, which means that although the range is controlled and is known, the brain cannot “predict” the order of the frequencies and doesn’t adapt to them.
“A good example to explain the phenomenon of the random frequency is comparing to when you smoke”, said Rita Donato, one of the study authors and current researcher at the Proaction Lab from the University of Coimbra, Portugal. “The first cigarette has a greater effect because you haven’t smoked for a while, but after two months of smoking, you don’t feel the smoking effect as much”. According to the PhD student, the same thing happens with the brain, that is, if you stimulate the brain with the same frequency it adapts to it, thus, a random frequency current stimulates the brain’s neurons in a non-expectable way.
This randomness impact makes the frequency to play an important role. Scientists wondered if the effect on the motor cortex on previous studies was working because of the use of a high frequency or if the range of the frequencies would hold the piece of the puzzle. The protocol for most tRNS studies was using a specific large frequency range, and not narrower subranges (1). “We decided to test if we could increase the brain excitability by using smaller scopes, these being 100-400Hz and 400-700Hz, while also testing a wider range of frequency similar to the protocol: 100-700Hz”, Rita Donato added.
The team from the University of Padova in Italy now demonstrated that using a wider range of a high-frequency band is more effective than using narrower ones. This means that the efficiency of the technology can be happening not because of the use of specific frequencies but because of the use of a range with a lot of random different frequencies.
The study of the motor cortex is a very noticeable way for study tRNS itself. By inducing this alternating current in that specific brain region scientists can induce the spontaneous movement of a hand and record the results.
The study collected data from 14 female students that had their motor cortexes stimulated. The generated hand’s movement was documented and then the data was analysed. “We realized that a wide frequency range seems to yield a more pronounced effect”, Rita Donato explained. “Our findings brought some awareness and I think in science things should be explained”, the researcher added. The study was done with a high-frequency band. Next step should be to do the study with a low-frequency band and see if it is possible to obtain similar results.
According to the PhD student, the application of some of these techniques is already happening for patients with motor and mental disorders, but further research is still necessary in order to use tRNS in clinical projects. However, other similar procedures are already being used to treat certain conditions. The application of tDCS, the Transcranial Direct-Current Stimulation is being used to enhance linguistic, mathematical and cognitive abilities (9). “It is exciting that the application of tDCS is improving visual acuity and also helping amblyopic patients [these patients have a problem with one eye that works less than the other]”, the researcher stated. The electrical stimulation improves the quality of life of those patients, so clinical application of electric stimulation is indeed possible.
People sometimes fear what they do not know, but after all, a little bit of electrical current in the brain can go a long way.
About the Authors: Rita Donato obtained her M.Sc. degree in Cognitive Neuroscience and Clinical Neuropsychology at the University of Padova. Currently, she is a third-year visiting research student at the Proaction Laboratory (Laboratory for the Perception and Recognition of Objects and Actions) of the University of Coimbra. Her project is focusing on the role of the dorsal and ventral stream in visual object processing using the functional magnetic resonance imaging (fMRI).
Moret, B., Donato, R., Nucci, M. et al. Transcranial random noise stimulation (tRNS): a wide range of frequencies is needed for increasing cortical excitability. Sci Rep 9, 15150 (2019) doi:10.1038/s41598-019-51553-7
Ghin, F., Pavan, A., Contillo, A. & Mather, G. The effects of high-frequency transcranial random noise stimulation (hf-tRNS) on global motion processing: An equivalent noise approach. Brain Stimul. 11, 1263–1275 (2018).
Pavan, A. et al. Modulatory mechanisms underlying high-frequency transcranial random noise stimulation (hf-tRNS): A combined stochastic resonance and equivalent noise approach. Brain Stimul. (2019).
Romanska, A., Rezlescu, C., Susilo, T., Duchaine, B. & Banissy, M. J. High-frequency transcranial random noise stimulation enhances perception of facial identity. Cereb. Cortex 25, 4334–4340 (2015).
Chan, H. N. et al. Treatment of major depressive disorder by transcranial random noise stimulation: Case report of a novel treatment. Biol. Psychiatry 72, e9–e10 (2012).
Palm, U. et al. Effects of transcranial random noise stimulation (tRNS) on affect, pain and attention in multiple sclerosis. Restor. Neurol. Neurosci. 34, 189–199 (2016).
Stephani, C., Nitsche, M. A., Sommer, M. & Paulus, W. Impairment of motor cortex plasticity in Parkinson’s disease, as revealed by theta-burst-transcranial magnetic stimulation and transcranial random noise stimulation. Parkinsonism Relat. Disord. 17, 297–298 (2011).
Terney D. et al. Increasing Human Brain Excitability by Transcranial High-Frequency Random Noise Stimulation. Journal of Neuroscience 28 (52) 14147-14155 (2008).
Brasil-Neto J., Learning, Memory, and Transcranial Direct Current Stimulation. Frontiers in Psychiatry 3, 80 (2012).
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