Neruomodulation is the alteration of neural activity through the use of some stimulus to modulate the behavior of neural pathways. Some common non-invasive methods used for neuromodulation are transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcranial magnetic stimulation (TMS). Neuromodulation can be effective at different stimulus intensities even if they are below the firing threshold of the intended target of stimulation. This versatility allows for many different applications of neuromodulation.
In 'Neuromodulatory Interventions for Traumatic Brain Injury' researcher Dr. Theresa Pape makes a case for the use of TMS as a treatment for traumatic brain injury (TBI). TBI can be defined as an alteration of brain function or pathology caused by an external force such as a collision playing football or a car accident. TBI can range from mild to severe where there is minimal loss in consciousness with mild TBI and an extended loss of consciousness possibly lasting years in severe TBI. In one part of her study Dr. Pape focused on the use of TMS paired with rehabilitation exercises to improve recovery after mild TBI. TMS can induce or enhance plasticity in a targeted neural network that, when paired with rehabilitation exercises, can help reshape or retrain neural pathways to improve behavior impacted by the TBI. While this has been shown to be effective for patients with mild TBI a different approach is required for severe TBI patients as they cannot engage with the same rehabilitation techniques.
The current industry standard treatment for patients with severe TBI is amantadine which is a drug that has been shown to promote functional recovery after severe brain injury. However many patients remain in a vegetative or minimally conscious state for years even with amantadine treatment. In a pilot study Dr. Pape paired TMS with amantadine and found that the paired treatment was more effective than amantadine alone or TMS alone. The study only contained four patients but is a promising result that requires more investigation.
While treating TBI is an effective application for the use of TMS it can also be effective in treating other brain injuries. Strokes effect hundreds of thousands of people a year and often lead to issues with motor function, cognitive function, and memory. The article 'Effects of high-frequency repetitive transcranial magnetic stimulation over the contralesional motor cortex on motor recovery in severe hemiplegic stroke: A randomized clinical trial' y Qi Wang et al. explored the use of TMS to promote the recovery of motor function after a hemiplegic stroke.
Hemiplegic strokes typically cause paralysis to one side of the face and body and are the result of damage to corticospinal tracts in one hemisphere of the brain. In their study Dr. Wang found that treating the damaged hemisphere of the brain with high-frequency TMS was no different from sham stimulation but that treating the healthy hemisphere with Hf-TMS showed significant improvement in motor function. This is because inducing plasticity in the healthy portion of the brain allows for the development of new pathways or modification of existing ones to compensate for the loss of function in the damaged portion of the brain. Treatment attempts with low-frequency TMS were not shown to be effective in the recovery of motor function.
The ability for TMS to enhance plasticity is an incredibly powerful tool for treating brain injury that could have potential for many other applications such as memory disorders and mental illness. However there are still some obstacles that need to be overcome. TMS is expensive, time consuming, and is not very portable which limits the access the average patient has to it. The risks it poses to patients are also not fully understood which make it difficult to get clinical trials approved. As we saw in the study with stroke patients the frequency of stimulation and region targeted are still not completely understood and require more investigation. As a whole neuromodulation is a promising tool for treating neurological ailments but more research is needed to make sure it is safe and accessible for the patients it would benefit.
References:
Pape, T. L., Herrold, A. A., Guernon, A., Aaronson, A. & Rosenow, J. M. (2020). Neuromodulatory interventions for traumatic brain injury. Journal of Head Trauma Rehabilitation, 35(6), 365-370. https://doi.org/10.1097/HTR.0000000000000643
Wang, Q., Zhang, D., Zhao, Y., Hai, H. & Ma, Y. (2020). Effects of high-frequency repetitive transcranial magnetic stimulation over the contralesional motor cortex on motor recovery in hemiplegic stroke: A randomized clinical trial. Brain Stimulation, 13(4), 979-986. https://doi.org/10.1016/j.brs.2020.03.020
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