Why might rTMS be useful in the treatment of Aphasia?
After a brain injury and starting in the acute phase, changes occur in the organisational pattern of nerve networks that were not completely damaged. This is what we mean when we talk about neuroplasticity. Said plasticity depends on genetic factors, but also the different connection patterns we have developed during our life or that we may learn in the future. Nevertheless, these phenomena are not always positive for the functionality of a person with brain damage; there are also those which are known as “maladaptive changes”.
Rehabilitation is aimed at guiding this capacity for change so that it is functional for the patient, but we are still discovering all the mechanisms that guide these plasticity phenomena.
In our brain there is a balance between the two brain hemispheres, which are interconnected, and connected to other networks, by inhibitory pathways that travel through the corpus callosum and modulate the activity of said hemispheres. After an injury that primarily affects one of the hemispheres, the balance is broken and there is an increase in activity in the healthy hemisphere.
Classically, it was believed that increased activity in the healthy regions after an injury was a compensatory mechanism of the injury. Today we know that some of these changes occasionally form part of the manifestation of the disease. A lot of data suggests that the excess activity in healthy regions hinders a more functional reorganisation of the neurons that survived in the affected region.
With TMS we can increase or inhibit the excitability of specific regions of the cerebral cortex in a safe and controlled manner. We can educe the inhibition that comes from the contralateral hemisphere or increase the excitability of undamaged areas that are close to the injury, and optimise the results of rehabilitation procedures, as is the case of motor aphasia.