Mechanisms triggered by transcranial magnetic exposure

Overview of current research

Abstract

The review attempts to describe the current understanding of the processes that occur in the brain during transcranial magnetic stimulation (TMS). It was shown that this effect is often used in attempts to activate speech processes in children, primarily boys. The study specifies the reason why speech problems are more common in boys compared to girls. It is noted that the physiological distribution of TMS is difficult to model, because the cerebrospinal fluid as well as white and gray matter have different conductivity. First, I propose three early hypotheses linking the changes in the brain and TMS: the disorganization of network activity; the competition hypothesis, which implies that TMS suppresses neural activity, i. e., reduces the signal but does not add noise; and the hypothesis that the brain improves signal detection at lower activity intensity. The emergence of new technologies made it possible not only to test these hypotheses but also to find out possible changes in the state of brain tissue activity at the site of TMS exposure. The article describes the results of the studies in which TMS was performed in parallel with EEG measurements and functional tomography and presents the data obtained during stimulation of the prefrontal cortex, sensory cortex and parietal region. These technologies made it possible to show that changes in the activity of brain neurons occur not only at the site of SCI impact but also in distant deep structures. The most important result was that weakly active populations of neurons and neurons that were activated before exposure to TMS were activated to the greatest extent during TMS. This result suggests that TMS will be particularly effective when used on children with speech problems if a speech task is presented immediately prior to exposure.