When a brain injury is suffered, depending on the areas that have been damaged, there will be an impact or another on the behavior and cognition. For example, those patients who suffer from Broca's aphasia will have damaged part of their temporal lobe of the left hermisphere. Nevertheless, brain damage not only stays in the affected area, but a cerebral decompensation occurs between the two hemispheres called interhemispheric competition. At this point, the main questions are, what is this competition and how can it be compensated?
Neuropsychology advances faster and faster. The discovery of new tools and techniques, allow the exploration of the brain in more detail and perform interventions more accurately and safely. One of the biggest headaches of researchers is the to be able to intervene and investigate the brain without invading it and without damaging it. Until a few years ago, this seemed quite unlikely, but with technological advances transcranial magnetic stimulation appeared. What is one of the possible applications of this technique? Compensate for interhemispheric competition.
Throughout this article, the concept of interhemispheric competition will be deepened and the positive effects that transcranial magnetic stimulation (TMS) can have on this brain disorder can be seen.
- 1 Interhemispheric Competition
- 2 Transcranial magnetic stimulation
- 3 Interhemispheric competition and TMS
When the cerebral hemispheres are in a state of rest, they maintain a constant interaction. This interaction is dynamic, stable and balanced, and is carried out through an interaction in which the hemispheres are excited and constantly inhibit each other. For example, if the right hemisphere gets too excited, the left hemisphere inhibits it, and vice versa. In this way, in a state of rest, this balance is created.
Nevertheless, when some kind of brain damage occurs this balance disappears. The damaged hemisphere will become hypoactive and due to this it will not be able to correctly exert the inhibition on the healthy hemisphere. In this way, the healthy hemisphere will become hyperactive and when hyperactivated the inhibition on the damaged hemisphere will be greater. In summary, the damaged hemisphere will not only become hypoactive due to the injury, but also, the healthy hemisphere will inhibit it even more. The greater this imbalance, the worse the prognosis for the recovery of cognitive deficits.
Transcranial magnetic stimulation
As Ibiricu and Morales (2009) describe: “Transcranial magnetic stimulation is a non-invasive method to electrically stimulate the cerebral cortex and to assess the excitability of the motor cortex and the corticospinal tract. ” One of the challenges of neuropsychology was to have within its reach a non-invasive method that allowed the brain to intervene. For this reason, TMS (of its acronym in English) turns out to be so important. The stimulation produced by TMS can be both excitatory and inhibitory, that is, in the same way that an area of the brain can be activated, it can be “deactivated”.
The TMS is a magnetic stimulator consisting of a coil connected to one or more capacitors that stores a large amount of electrical energy and can be discharged in a very short period of time. As the Malavera team (2014) describes, “The stimulation coil consists of a fully insulated copper wire material coated with a plastic mold. With the active coil, the magnetic field easily penetrates skin, skull and meninges and induces a secondary electrical current in the brain tissue”. In this way, brain activity can be modulated safely.
To generate a magnetic field with sufficient intensity to stimulate the cortex, the current must be between seven and ten kiloamperes and is applied in a pulse lasting one millisecond. Through the current that induces the magnetic field, axons of both the cerebral cortex and the subcortical and underlying white matter are activated. Thus, The electric current will be applied to areas of the cerebral cortex as well as to other subcortical points that receive projections of the area on which the stimulation is taking place.
Interhemispheric competition and TMS
Through this technique, those with a damaged cerebral hemisphere could benefit. As we have seen, when there is an injury in a hemisphere, it becomes hypoactive and also receives an over-inhibition of the healthy hemisphere. With the help of low frequency TMS, the hyperactivity of the healthy hemisphere is reduced and, in this way, it will stop over-inhibiting the damaged hermisphere. Through this method, it is intended that the damaged hemisphere can function in the best possible way without the over-inhibition produced by the healthy hemisphere.
Ibiricu, M. and Morales, G. (2009). Transcranial magnetic stimulation. Annals of the health system of Navarra, 32 (3), 105-113.
Malavera, M., Silva, F., García, R., Rueda, L. and Carrillo, S. (2014). Fundamentals and clinical applications of transcranial magnetic stimulation in neuropsychiatry. Colombian Journal of Psychiatry, 43 (1), 32-39.