What kind of Impact does TMS make in the Brain?

A Visual Cortex Study

Researchers at the Ruhr University in Bochum/Germany have obtained new findings on the question of how Transcranial Magnetic Stimulation (TMS) affect the functional connectivity of the neurons. In order to visualize the effects, they used fluorescent dye, providing data over the activation of the neurons with light. Using this technique, they showed that TMS affected the neuronal connections in the visual cortex of the brain for the restructuring process in animal patterns.

Although TMS is utilized for the treatment of a series of psychiatric and neurological brain diseases, such as depression and Alzheimer’s disease, there are very few studies on how exactly TMS works. Assoc. Prof. Dirk Jancke, MD, and his team from the Optical Imaging Laboratory in Bochum told The Proceedings of the National Academy of Sciences* about the new findings they obtained.

An analysis of its effects over the cortical maps located in visual cortex

Researchers investigated how TMS practices affected the organization of the orientation maps deemed to be located in the visual region of the brain. (These maps are partially determined genetically and shaped by our interactions with our surroundings) For instance, neurons typically react to the contrast edges of specific directions that create the borders of the objects in the visual cortex. While the neurons, which preferably respond to the edges of a specific orientation, are grouped closely, clusters of neurons having other orientation preferences are slowly placed further and they therefore create a completely systematic map throughout all orientations.

The research team compared the behavior of the neurons with a specific pre-procedure and post-procedure angular orientation, using TMS as well as visual stimuli. Conclusion: The neurons gave more variable responses following the magnetic stimulation. Therefore, this means specific orientation preferences were less apparent prior to the TMS procedure. “You may say that the neurons were a little unstable following the TMS and that they were potentially open to new tasks in turn. Accordingly, we inferred that the treatment provided us with a time interval for the induction of the plastic processes, in which the neurons may change their functional preferences.

The maps are reshaped by implementing TMS along with a brief visual training

Subsequently, the team researched the effects of a passive visual training following a TMS treatment. A 20-minute exposure to a specific angular orientation image caused an expansion of the regions where the visual training of the brain took place. “This type of procedure could be a helpful approach for therapeutic interventions and for specific sensorimotor training forms”, says Dirk Jancke about the post-study scenery.

Methodological challenges

Transcranial magnetic stimulation is a non-invasive, painless procedure. A coil/helmet/headpiece is placed on the head, and the brain region in question can be activated or inhibited through magnetic waves. The magnetic field is analyzed through electrical measurement techniques, such as EEG in particular, and additionally via functional magnetic resonance imaging methods.

Dirk Jancke’s team used tension-dependent fluorescent dyes embedded into the membranes of the neurons in order to measure the brain activity after the TMS for the purpose of obtaining a higher resolution result, instead of EEG and fMRI. As soon as a neuron’s activity was modulated, the dye molecules changed their emission densities. Therefore, light signals could provide information about the sudden changes in the activity of the neuron groups.

In brief, this study, which discussed the cortex connections in maps before and after the TMS procedure implemented on the visual cortex, aimed to display the changes in the neuron through clearer imaging techniques. It was observed that the neuron activities increased following the TMS procedure, and it was concluded that this situation positively affected the maps on the visual cortex.

* Proceedings of the National Academy of Science (PNAS)

KAYNAK:

• Vladislav Kozyrev, Robert Staadt, Ulf T. Eysel, Dirk Jancke. TMS-induced neuronal plasticity enables targeted remodeling of visual cortical maps. Proceedings of the National Academy of Sciences, 2018; 201802798 DOI: 10.1073/pnas.1802798115, ScienceDaily.