Insight Into the Effects of Clinical Repetitive Transcranial Magnetic Stimulation on the Brain From Positron Emission Tomography and Magnetic Resonance Imaging Studies: A Narrative Review

Abstract

Repetitive transcranial magnetic stimulation (rTMS) has been proposed as a therapeutic tool to alleviate symptoms for neurological and psychiatric diseases such as chronic pain, stroke, Parkinson’s disease, major depressive disorder, and others. Although the therapeutic potential of rTMS has been widely explored, the neurological basis of its effects is still not fully understood. Fortunately, the continuous development of imaging techniques has advanced our understanding of rTMS neurobiological underpinnings on the healthy and diseased brain. The objective of the current work is to summarize relevant findings from positron emission tomography (PET) and magnetic resonance imaging (MRI) techniques evaluating rTMS effects. We included studies that investigated the modulation of neurotransmission (evaluated with PET and magnetic resonance spectroscopy), brain activity (evaluated with PET), resting-state connectivity (evaluated with resting-state functional MRI), and microstructure (diffusion tensor imaging). Overall, results from imaging studies suggest that the effects of rTMS are complex and involve multiple neurotransmission systems, regions, and networks. The effects of stimulation seem to not only be dependent in the frequency used, but also in the participants characteristics such as disease progression. In patient populations, pre-stimulation evaluation was reported to predict responsiveness to stimulation, while post-stimulation neuroimaging measurements showed to be correlated with symptomatic improvement. These studies demonstrate the complexity of rTMS effects and highlight the relevance of imaging techniques.

Cerebral blood flow changes induced by high-frequency repetitive transcranial magnetic stimulation combined with cognitive training in Alzheimer's disease

“…Finally, additional measurements such as task fMRI or resting-state fMRI were not conducted to further clarify what exactly happened at the functional connectivity level. Because the effects of rTMS are complex and involve multiple neurotransmission systems, regions, and networks ( 54 ), further studies combining TMS with imaging studies would advance our understanding of the neurobiological underpinnings of rTMS, either using positron emission tomography (PET) or MR techniques.…”

An Exploratory Study of a Novel Combined Therapeutic Modality for Obsessive-Compulsive Disorder

“…Bidet-Caulet et al pointed out that the prefrontal lobe was closely related to cognitive function [ 40 ]. Therefore, we can further postulate that CBT and repeated high-frequency rTMS at the prefrontal lobe could modulate cortical excitement, activeness and plasticity [ 41 ], which induces the changes of Dopamine and other neurotransmitters [ 42 ], leading to changes in brain functional connection and microstructural change of the white matter [ 43 , 44 ] and finally participating in improving the insight of OCD patients. This may be the mechanism of CTM in improving the insight of OCD patients, though further study is required to verify our postulation.…”

Potential Applications of Motor Imagery for Improving Standing Posture Balance in Rehabilitation

“…Transcranial magnetic stimulation (TMS) is a technique that noninvasively modulates brain activity through the induction of currents by rapidly changing magnetic field pulses [50]. In addition, by reviewing the literature through 2018, guidelines were established for treatment with repetitive transcranial magnetic stimulation (rTMS) in Europe in 2020.…”