Abstract
Throughout history, many have searched for ways of stimulating the brain non-invasively. However, it was technically impossible until 1985 when Barker, Jalinous, and Freeston introduced a novel method of brain stimulation using magnetic fields which led the path towards the specialty discipline of non-invasive brain stimulation (NIBS). In recent years, there have been several advances in NIBS techniques especially transcranial magnetic stimulation (TMS)/repeated transcranial magnetic stimulation (rTMS), including the development of new stimulation protocols such as high-frequency TMS and intermittent theta burst stimulation, which have shown promising results in the treatment of mental health conditions. The development of new, more portable and user-friendly stimulation devices has made it easier for researchers and clinicians to use NIBS in different settings and for different patient populations. There is growing evidence for the use of NIBS in combination with other forms of therapy, such as cognitive behavioral therapy (CBT), to enhance its therapeutic effects. Researchers are exploring the utility of neuroimaging techniques, such as functional magnetic resonance imaging (fMRI), to guide the placement of stimulation electrodes and customize stimulation protocols for individual patients. Advances in neuroimaging and neurophysiology have helped researchers better understand the NIBS’ mode of action, leading to the development of more targeted and effective stimulation protocols. It was believed that, unlike most other surgical and medical subspecialties, psychiatry will never undergo technical advancements because it mainly relied on pharmacotherapy and psychotherapy to direct patient care. However, with the advent of NIBS, the field had relative progress. Currently, there are about seven FDA-approved TMS instruments for the treatment of various psychiatric and other medical conditions. But it was reported that these devices produce differences in terms of treatment outcomes. For example, when TMS is administered using the NeuroStar and MagVenture devices, there is a significant variation in the average time to remission for major depressive disorder. It was found that the average time to remission was shown to be shorter for patients treated with the MagVenture instrument, and their rates of overall 6-week remission were higher, as well as their rates of enhanced CBT response. 1 These findings prompt the following questions: Are TMS devices comparable, and if not, which one should be the gold standard of care?
Based on the research data published related to craving/addiction, schizophrenia, depression, anxiety disorders, obsessive compulsive disorder, conversion, and other medical conditions until March 2014, the guidelines were formulated for the therapeutic use of rTMS. Only one condition connected to mental health had sufficient body data to accept it at a level of certain efficacy (Level A), and that was the anti-depressant action of high-frequency rTMS over the left dorsolateral prefrontal cortex (DLPFC). High-frequency rTMS of the left DLPFC was suggested to have Level B, that is, probably efficacy, for the negative symptoms of schizophrenia. Low-frequency rTMS of the right DLPFC was also recommended for antidepressant action. For several other mental health conditions, a level C recommendation (potential efficacy) has been put forth such as auditory hallucination (low-frequency rTMS of the left temporoparietal cortex), post-traumatic stress disorder (high-frequency rTMS of the right DLPFC), cigarette consumption (high-frequency rTMS of the left DLPFC). 2 However, there is more work to be done to determine how to optimize stimulation parameters in everyday clinical practice.
The expert discussion that took place at the National Institutes of Health in June 1996 is still used as a reference for current safety measures, forming useful suggestions, and setting treatment guidelines. Also, numerous clinical researches have been conducted to decipher the associated risks of the TMS/rTMS administration. The possibility of inducing a seizure during the stimulation session is the most severe danger associated with rTMS, but it is also the least likely. The possibility of hearing loss due to the loud clicks of TMS is another issue, but this risk can be reduced by using earplugs. Also, the patients have reported headaches and pain at the delivery site as a side effect of TMS; however, these symptoms are transient and can be treated with analgesic drugs. The use of rTMS in treating depression has been FDA-approved for more than a decade and is currently offered in many places. Most of the patients who were availing treatment in a United States-based tertiary NIBS center reported that they learnt about TMS as a treatment option on their own and requested a referral for TMS from their psychiatrist. 3 However, many psychiatrists do not consider this treatment option at least when the USA is considered for this matter. This also poses the question: Whether the psychiatrists lack the necessary education on TMS/rTMS to consider it as a complementary therapy other than/to psychotropic medications?
Also, the data remains unknown for the frequency of referrals made for TMS/rTMS in the jurisdiction of other developed and developing countries. Hence, both physician and patient education should be emphasized. Maybe in the seemingly near future, as indications are established in disciplines other than psychiatry, the difficulty of training and educating physicians will probably resurface. One way to counter such shortcomings could be implementing nationwide super specialty and fellowship courses in NIBS and shifting focus towards introducing NIBS-related journals.
The last two decades have seen a heavy rise in the applications of TMS/rTMS to study human cognitive function, neuropsychology, and the pathophysiology of various neurological and psychiatric morbidities. Yet as of now in psychiatry the literature is limited to treatment-resistant depression among adults, limited studies have explored the efficacy in children with primary diagnoses of autism spectrum disorder, attention deficit hyperactivity disorder, and Tourette’s syndrome. 4 Findings about the utility or preliminary efficacy of rTMS as a treatment varies across the body of literature that is currently available, in part because of obvious reasons such as different protocols have been used, the chance of bias based on the clinical trial designs that have been used so far, variability of the research samples, and utilizing different outcome measures. Henceforth, the NIBS related research must be addressing the consistent limitations which were highlighted in the literature such as: carrying out trials in accordance with the guidelines for drug clinical studies, increasing the size of the samples and employing realistic placebo control and double blinding, use of cutting-edge statistical techniques including cluster analysis and randomized cross-over study designs, by utilizing neuro-navigated TMS to improve anatomical targeting, supporting new research to identify novel, attainable stimulation targets, raising the stimulation dosage, which has generally been low in numerous investigations, systematic application of priming techniques to enhance the effects of NIBS, identifying and enhancing clinically valid endpoint measures, exploring the use cases of NIBS in other clinical population. It is important to note that these advances in NIBS and safety profiles are promising, more research is needed to fully understand the potential benefits and limitations of NIBS, and to develop best practices for its use in clinical practice.