TMS & Other Therapies

How Does Transcranial Magnetic Stimulation Change the Brain?

November 17, 2018

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While recent research continues to show the success of Transcranial Magnetic Stimulation (TMS) on treating non-responsive depression, OCD, PTSD, and more, the exact manner in which the treatment changes the brain is still being research.

TMS is a form of brain stimulation derived from similar simulations, like Electroconvulsive Therapy, where parts of the brain believed to control mood are stimulated to alleviate symptoms of depression. It is generally understood these stimulation help balance the neural pathways connected to mood. Little is know, however, about how TMS impacts the brain on a cellular level.

brain neuron cells
How does TMS affect the brain on a cellular level?

Neural Mapping Orientation

Until now it has remained unclear how the relatively nonspecific nature of TMS leads to specific neuronal reorganization. They are also missing a detailed picture of TMS-triggered reorganization of functional brain modules.

While it it generally believed that the adult central nervous system remains relatively fixed, this is some evidence the cortical networks can be remodeled through perceptual training or experiences. The environment and mechanism to do so though is up for debate. TMS is showing promise to help to reorganize the networks in a non-invasive way.

To attempt begin to understand more clearly the impact of TMS more deeply, researchers at Ruhr-Universität Bochum used real-time optical imaging in an animal experimental setting to track functional changes in visual feature maps over several square millimeters of the brain during TMS treatment.

To do so they injected fluorescent dyes that share information on the activity of neurons through light. They were then able to show that TMS predisposes neuronal connections in the visual cortex of the brain for processes of reorganisation.

fluorescent colored brain illustrations
Fluorescent dyes were used to visualize neural activity.

What this reveals is that TMS creates a temporary cortical state, where neurons display increased excitability and increased response variability, which enables a short window of adaptability. The team of associate professor Dr Dirk Jancke of the Optical Imaging Lab in Bochum describes its new discoveries in the journal Proceedings of the National Academy of Science (PNAS).

Studying Effects of TMS on the Visual Cortex

To test how TMS affects the reorganization of the brain’s neural networks, the researchers investigated the visual part of the brain. The organizational maps are partly genetic, and partly shaped by one’s environment. In the visual cortex, neurons react to contrast edges of certain orientations, helping to define the boundaries of objects. Neurons that prefer to respond to edges of a specific orientation are closely grouped whereas clusters of neurons with other orientation preferences are gradually located further away. Together these neurons form a systematic map across all orientations.

Researchers utilized high frequency TMS and analyzed the behavior of neurons after visual stimuli with a specific angular orientation, before and after treatment. They discovered that after TMS the neurons response was less pronounced, more variable to specific orientations. In a way, after treatment neurons where potentially open to new tasks.

Next they analyzed the impact of a 20 minute passive visual training after TMS treatment. During the training there was exposure to images of a specific angular orientation. They found this led to the areas of the brain that represent the training orientation were enlarged. This showed that to modify the brain’s connectivity patterns or maps, offering specific “training” after TMS can help reorganize neural pathways. The researcher believe this can prove to be a very helpful approach therapeutic interventions.

how neural mapping helps visualize the visual cortex after TMS
This research suggests that TMS may work by destabilizing neurons in the visual cortex, making it more adaptable, which then allows it to be remodeled. This further suggests that "training" after TMS can be helpful, as it may help reorganize neural pathways. Image courtesy of BrainPost

As research continues, and a deeper understanding of how TMS is affecting the brain’s neural networks emerges, this data can inform better ways to optimize the impact of TMS in therapeutic treatment.

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