In 1991, one of the first scientific papers reporting the use of repetitive TMS was published by Alvaro Pascual-Leone, now a professor of neurology at Harvard Medical School, and his colleagues. In this study, the research team observed that the application of repetitive TMS to regions of the left hemisphere of the brain could interrupt speech production, a phenomenon sometimes referred to as a “speech arrest” (Horvath et al., 2010). A few years later, in 1995, Kolbinger and his colleagues, affiliated with universities in Germany and Austria, were among the firsts to publish the results of a proof-of-concept study (i.e., a study aimed at showing the feasibility of an innovation) in which repetitive TMS was used in people with major depression refractory to pharmacological treatments. A reduction in symptoms was observed following the TMS treatment (Kolbinger et al., 1995).

In the late 1990s, research teams combined TMS with neuroimaging techniques such as magnetic resonance imaging (MRI) and positron emission tomography (Horvath et al., 2010). These studies showed that TMS affected brain activity directly underneath the coil, but also in nearby regions, though with a reduced magnitude (e.g., Paus et al., 1997).

From the beginning of the use of TMS, several ethical considerations have been raised. These considerations included the safety of TMS devices, as well as potential long-term side effects (Horvath et al., 2010). These considerations led to the publication of the first safety guidelines for the safe usage of TMS in 1998 by Wassermann (Horvath et al., 2010). Since that time, other international safety guidelines have been published and then revised to minimize the risks associated with TMS (Rossi et al., 2009 and 2020). These guidelines are rigorously followed by the members of our laboratory, which are also trained by Dr. Pascale Tremblay on the principles and safety of TMS.

Over the years, TMS has proven to be an important research tool in the field of neuroscience and psychiatry, to study the functioning of the brain and spinal cord in healthy people or people with neurological or psychiatric disorders.  It is a tool that we use in our laboratory to understand how the brain allows us to perceive and produce speech. On the clinical side, repetitive TMS was approved in 2002 by Health Canada. It was also approved by the US Food and Drug Administration (FDA) for the treatment of drug-resistant depression in 2008, migraines in 2013, and obsessive-compulsive disorder in 2018 (Horvath et al., 2011; Stultz et al., 2020). TMS is used as a therapeutic tool in the clinic, since it can induce medium—or long-term changes in the excitability and connectivity of neural networks (Ziemann, 2017), a phenomenon called “plasticity induced by experience.”

Finally, research is still ongoing to better understand how TMS affect brain activity, its mechanism of action. One approach is to TMS with neuroimaging techniques such as electroencephalography, or mathematical modelling techniques, making it possible to visualize the distribution of the electric field following stimulation. Hence, the history of the TMS is still being written!