Kakuda and his team are investigating the potential of repetitive transcranial magnetic stimulation (rTMS) to be implemented in stroke rehabilitation. TMS is a non-invasive procedure that is typically used to help improve symptoms of depression. To do this, it uses magnetic fields to
stimulate nerve cells in the brain. rTMS is another form of brain stimulation therapy used in the treatment of depression and anxiety. Kakuda explains more: ‘The first report of TMS application for humans was published in the Lancet in 1985 by English neurologist, Anthony Barker. He
successfully moved the hand of the subject with TMS applied over the contralateral motor area of the brain. The mechanism of TMS is based on Faraday's Law of Induction. The current passing through a stimulating coil placed over the head can produce a magnetic field, which penetrates the skull
and reaches the brain. After that, an ionic current is produced in the cerebral cortex by magnetic stimulation and the current stimulates the neuron in the cerebral cortex.’ In TMS, a magnetic field is generated by an electric current flowing through a stimulating coil. This induces
electric currents in the brain, stimulating neurons. In rTMS, the effect of the treatment on cortical excitability is dependent on the frequency of stimulation. For example, in high-frequency rTMS, there is a facilitatory affect, with an increase in cortical excitability, while low-frequency
rTMS has a suppressive effect, and a decrease in cortical excitability is seen. Kakuda explains more: ‘Low-frequency rTMS is defined as rTMS of less than or equal to 1 Herz. High-frequency rTMS is defined as rTMS of more than or equal to 10 Herz. Low-frequency rTMS can decrease local
neural activity of the brain (which means it’s suppressive), whereas high-frequency rTMS can increase the activity (which means it’s facilitatory). Therefore, the effect of rTMS can be bi-directional based on the frequency of stimulation. When the activity of the pathologically
hypoactive area of the brain needs to be increased therapeutically, high-frequency rTMS should be applied over the area. This neuromodulation effect of rTMS is mainly due to the changes in synaptic efficiency. For example, high-frequency rTMS can enhance synaptic efficiency in the stimulated
areas of the brain.’ As such, the researchers’ determined that high-frequency rTMS should be used for up-regulation, with direct activation of the compensatory area, whereas low-frequency rTMS is appropriate for down-regulation, whereby neural activity in the hemisphere is contralateral
to compensatory areas and there is a reduction of interhemispheric inhibition towards compensatory areas and disinhibition of compensatory areas and indirect activation of the areas. The team also found that with rTMS, neural plasticity should be enhanced prior to rehabilitative training.
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