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Enhancing brain plasticity through strong magnetic waves

New study of Dirk Jancke published in PNAS (Proceedings of the National Academy of Sciences of the United States of America)


Optical imaging of TMS-enhanced cortical plasticity

Our perception is based on the brain’s complex activation patterns triggered through all sorts of sensory input, no matter if we listen to music, touch an object or explore our surroundings. At early stages of cortical processing, specific stimulus characteristics are topographically arranged within so-called feature maps. When we are looking at a house, for instance, its outline and edges are encoded according to different orientations and represented at adjacent locations in the visual cortex of the brain. Yet, these maps are not fixed, but alterable; they can be reorganized by learning, during which the encoding areas can be reduced or enlarged in order to regulate the processing of sensory input flexibly and efficiently.

Brain areas can specifically be inhibited or activated

However, cortical maps are not only shaped by sensory input (e.g. optical, auditory or tactile), but can also be influenced by non-sensory external stimulation, as for instance through transcranial magnetic stimulation (TMS). In this non-invasive and painless method, a magnetic coil is being positioned above the head and the brain area in question can be activated or inhibited through magnetic waves. This facilitates the reorganization of neural connections and can be put to therapeutic use – currently, TMS is being used as a treatment for a number of neurological diseases such as depression, epilepsy, amblyopia („lazy eye” syndrome) or after a stroke.
Yet, investigating the neuronal effects of TMS on the level of neuronal circuits remains challenging. The strong magnetic fields superimpose the signals of other methods suitable to reveal the effects of TMS. For instance, the magnetic pulse interferes with electrophysiological monitoring techniques, such as EEG.

Neurons respond more variably after magnetic stimulation

Dirk Jancke’s team from the Optical Imaging Lab at Ruhr University Bochum showed how strong magnetic fields affect the functional interconnectivity of neurons using voltage-dependent dyes. The researchers employed high frequency TMS and compared how neurons reacted to visual stimuli before and after the procedure. The result: After the magnetic stimulation the neurons responded more variably. „You could say that after the TMS the neurons were somewhat undecided and hence, potentially open to new tasks”, explains Dirk Jancke. „Therefore, we reasoned that the treatment provides us with a time window during which neurons can change their functional preference.”

The researchers also investigated the impact of a passive visual training after TMS treatment. A 20 minute exposure to visual stimuli containing a certain edge orientation led to the enlargement of those brain regions whose cells revealed a strong preference for the presented edge orientation. „Thus, the map in the visual cortex quickly adapted to the new information content of visual stimulation,” explains Jancke. „The selective triggering of perceptual sensory or motor learning after application of TMS, could therefore be a possible approach for therapeutic measures as well as for certain kinds of sensorimotor training.” /njs
Modified after press release from Ruhr University Bochum, RUB

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Vladislav Kozyrev, Robert Staadt, Ulf Eysel, Dirk Jancke: TMS-induced neuronal plasticity enables targeted remodeling of visual cortical maps, in: PNAS, 2018, DOI: 10.1073/pnas.1802798115

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