Leaving Italy

How does the magnetic cortical stimulation work?

For this week’s post I will finally go back on the story of how I ended up doing a PhD in Germany and I will tell you about what I did after I graduated from my Master’s in Neurobiology.

Since I was still not sure about doing a PhD, I took advantage of the Erasmus post lauream traineeship and I decided to apply for it. This Erasmus project was brand new at the University of Pavia and it offered recent postgraduate students to spend a period of up to one year in a European University or research centre to work on project, in order to learn new techniques/help recent graduates to get into a working environment.

After applying to different places, I decided to join a group in Lyon working on neuropathic pain in the Centre for Neuroscience at the Hôpital Neurologique. This experience was very new and completely different from all the laboratory work I previously did: I had the chance to get acquainted with a number of techniques of human and clinical neurophysiology in the context of pain and somatosensory disorders, such as high-density electroencephalography (HD-EEG) from scalp recordings, stereo-EEG from intracerebral recordings in epileptic patients, somatosensory evoked potentials to A-delta and C-fiber activation by laser stimuli and data transformation (segmentation, correction, interpolation filtering, conditioned averaging, wavelet transformation, etc) for EEG analysis.

Apart from the very interesting experience of working with patients for the first time in my life (particularly hard in the beginning, since I was actually living in France and my knowledge of French was mostly limited to my middle school studies, even though it eventually got better while living there), what fascinated me the most was my participation in a program of cortical neurostimulation coupled with peripheral laser activation. Therefore, today for the SRF I would like to talk about the magnetic cortical stimulation for the treatment of pain.

“Science Related Fact” (SRF):

The Transcranial Magnetic Stimulation (TMS) is an advanced and very promising technique of non-invasive cortical stimulation that can be used for motor or cognitive disorders and some rare cases of chronic pain.

During TMS, a special metallic coil is applied on the scalp and it produces a magnetic field that passes through the scalp and skull, reaching the brain and generating a current that stimulates the cerebral cortex that lies below the coil (have a look below for a schematic of the TMS apparatus and the areas that can be reached by the magnetic field).

Schematics of the cerebral areas that can be stimulated with the TMS and a representation of the magnetic coil used to perform the technique. Modified from manorog.com

This current stimulates the nerve fibers and it produces different effects, depending on the stimulated area: for example, if we stimulate a motor area that controls the movements of the hand, we would be able to observe an involuntary contraction of the muscles of the hand. Moreover, this magnetic stimulus produces an adjustable response, that occurs as a sound similar to a click, and a sensation of skin tingling. The TMS stimulation is not painful and does not produce significant systemic side effects. The effects of this stimulation are both short and long-term: it is possible to modify the activation of one cerebral circuit after only one session, while after several sessions it is able to induce permanent changes by increasing the cerebral plasticity (in particular, by increasing the cerebral connexions between neurons and, consequently, the adaptation ability of the brain).

Usually, the TMS is repeated daily from two weeks to one month. After the first initial period, there are follow-up sessions that allow to consolidate the effects of the first initial month and prevent the risk of future set-backs.

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