Learn faster by magnetic brain stimulation

Bochum's researchers investigate the effect of TMS stimulus patterns specifically alter the activity of certain neurons

What sounds like science fiction is actually possible: Due to the magnetic stimulation from the outside can be the activity of certain brain nerve cells selectively influence. What it happens in the brain exactly was still unclear. Bochum physicians led by Prof. Dr. Klaus Funke (Department of Neurophysiology) have now shown that various stimulus patterns act in different cells and inhibit their activity or increase. Certain stimulus patterns led so mean that rats learning more easily.

The findings could help to that the brain stimulation can be used in future targeted against brain dysfunction. The researchers have published their studies in the Journal of Neuroscience and in the European Journal of Neuroscience.

Magnetic pulses stimulate the brain

Transcranial magnetic stimulation, or TMS for short, is a relatively new method for pain-free stimulation of brain nerve cells. The method, first introduced by Anthony Barker in 1985, is based on the fact that a magnetic field can be used to stimulate the cerebral cortex, the cortex, which lies directly under the cranial bone. TMS is used in diagnostics, in basic research and as a potential therapeutic tool. When used diagnostically, a single magnetic pulse is used to test the activation of nerve cells in a cortex area in order to assess changes in diseases or after taking medication or after previous artificial stimulation of the brain. A single magnetic pulse can also be used to test the involvement of a specific area of ​​the cortex in a sensory, motor or cognitive task, as it temporarily disrupts its natural activity, ie temporarily "switches off" the area.

Repeated stimuli alter brain activity

Since the mid-1990s, repetitive TMS has been used to specifically change how nerve cells in the human cortex can be activated: “In general, low-frequency stimulation reduces cell activity by one Hz, ie one magnetic pulse per second. At higher frequencies of five to 50 pulses per second, the activity of the cells increases,” explains Prof. Funke. The researchers are primarily concerned with special stimulus patterns such as the so-called theta burst stimulation (TBS). 50 Hz bursts (bursts) are repeated at 5 Hz. "This rhythm is based on the natural theta rhythm of four to seven Hertz, which can be observed in the EEG," says Funke. The effect depends primarily on whether such stimulus patterns are given continuously (cTBS, attenuating effect) or with interruptions (intermittent, iTBS, enhancing effect).

Contact points between cells are strengthened or weakened

How exactly the activity of nerve cells is changed by repeated stimulation is largely unknown. It is assumed that the contact points (synapses) between the cells are strengthened (synaptic potentiation) or weakened (synaptic depression) by repeated stimulation, a process that also plays an important role in learning. It was also recently shown that the effects of TMS and learning interact in humans.

Inhibitory cortex cells are particularly sensitive to stimulation

The Bochum researchers have now been able to show for the first time that artificial cortex stimulation specifically changes the activity of certain inhibitory nerve cells depending on the stimulus protocol used. The interaction of excitatory and inhibitory nerve cells is an absolute prerequisite for the healthy functioning of the brain. Neurons specialized for inhibition show a far greater variety of shapes and structure of activity than their excitatory partners. Among other things, they produce different functional proteins in their cell bodies. In his studies, Prof. Funke concentrated on examining the proteins parvalbumin (PV), calbindin-D28k (CB) and calretinin (CR). They are formed by various inhibitory cells depending on their activity, so that their amount provides information about the activity of the corresponding nerve cells.

Stimulus patterns have a special effect on certain cells

The investigations have shown, for example, that the activating stimulation with interruptions (iTBS stimulation protocol) almost only reduces PV formation, while the activity-dampening continuous stimulation (cTBS protocol) or a likewise dampening 1 Hz stimulation mainly reduces CB production reduce. CR formation was not altered by any challenge protocol tested. The registration of the electrical activity of nerve cells confirmed an altered inhibition of cortical activity.

Learn faster after stimulation

In a second study, recently published in the European Journal of Neuroscience, Prof. Funke's working group was also able to show that rats learn faster if they were treated with an activating stimulus protocol (iTBS) before each training session, but not if the inhibitory cTBS protocol was used. It was shown that the initially reduced formation of the protein parvalbumin (PV) was increased again by the learning procedure, but only in the brain areas involved in the learning process. In animals not engaged in the specific learning task, PV production remained reduced after the activating stimulation. "So the iTBS treatment initially reduces the activity of certain inhibitory nerve cells in general, so that the subsequent learning activities can be stored more easily," concludes Prof. Funke. “This process is called 'gating'. In a second step, the learning activity normalizes the inhibition and PV formation again.”

Treat more carefully in the future

Repetitive TMS is already being used on an experimental basis to treat brain dysfunction, particularly major depression, with limited success. In addition, it could be shown that functional disorders of the inhibitory nerve cells play an important role in neuropsychiatric diseases such as schizophrenia. "It is certainly still too early to derive new forms of treatment for functional disorders of the brain from the results of our study, but the findings make an important contribution to a possibly more specific application of TMS in the future," hopes Prof. Funke.

cover shots

Benali, A., Trippe, J., Weiler, E., Mix, A., Petrasch-Parwez, E., Girzalsky, W., Eysel, UT, Erdmann, R. and Funke, K. (2011) Theta- burst transcranial magnetic stimulation alters cortical inhibition. J. Neurosci., in press.

Mix A, Benali A, Eysel UT, Funke K (2010) Continuous and intermittent transcranial magnetic theta burst stimulation modifying tactile learning performance and cortical protein expression in the rat differently. In: Eur. J. Neurosci. 32(9):1575-86. doi: 10.1111/j.1460-9568.2010.07425.x. Epub 2010 Oct 18.

Source: Bochum [ Ruhr University ]