Magnetic stimulation has proven that reality can sometimes overtake fiction by proving that the activity of certain brain nerve cells can be deliberately influenced by changing the activity of distinct neuronal cell types.
Recent findings also included the discovery that certain stimulus patterns could result in rats learning more easily, which could now lead to cerebral stimulation being used to treat functional disorders of the brain in the future.
Transcranial magnetic stimulation (TMS) is a fairly recent method that consists in pain-free stimulation of cerebral nerve cells and was first presented by Anthony Barker in 1985. The method is based on the fact that the cortex, the rind of the brain located directly underneath the skull bone, can be stimulated by using a magnetic field. TMS has since then been used in diagnostics and research but has also proven to be a potential therapeutic instrument.
TMS has often been used in diagnostics relating to changes in deceases, or to the consumption of medications as one single magnetic pulse can help to test the activability of nerve cells in an area of the cortex. Experts have also pointed out that a single magnetic pulse can also be used to test the involvement of a certain area of the cortex in a sensorial, motoric or cognitive task, since it interfere with the area targeted and 'switches it off' for a short time.
For more than ten years repetitive TMS has also been used to make targeted changes to the activability of nerve cells in the human cortex. "In general, the activity of the cells drops as a result of a low-frequency stimulation, i.e. with one magnetic pulse per second. At higher frequencies from five to 50 pulses per second, the activity of the cells increases," Professor Funke, told Science Daily.
Researchers and Scientists are also particularly interested in the effects of distinct stimulus patterns like the so-called theta burst stimulation (TBS), in which 50 Hz bursts are repeated with 5 Hz. "This rhythm is based on the natural theta rhythm of four to seven Hertz which can be observed in an EEG," says Funke. The effect is above all dependent on whether such stimulus patterns are provided continuously (cTBS, attenuating effect) or with interruptions (intermittent, iTBS, strengthening effect).
Despite years of research, it is however still unknown how much repeated stimulation changes the activity of nerve but studies have shown that artificial cortex stimulation specifically changes the activity of certain inhibitory nerve cells. To continue functioning healthy, the brain needs a balanced interaction of excitatory and inhibitory nerve cells. However, compared to the excitatory nerve cells, inhibitory nerve cells show greater variety in terms of cell shape and activity structure while they produce several functional proteins in their cell body.
A recent study, led by professor Funke's group which was first published in theEuropean Journal of Neuroscience alsoshowed that rats also learned more quickly if they were treated with the activating stimulus protocol (iTBS) before each training, but not if the inhibiting cTBS protocol has been used.
While initially, formation of the protein Parvalbumin (PV) was reduced, it was rapidly increased after introduction of the learning procedure, but only in the areas of the brain involved in the learning process. "The iTBS treatment therefore initially reduces the activity of certain inhibiting nerve cells more generally, with the result that the following learning activities can be stored more easily," says the study.
Alsorepetitive TMS is currently used in clinical trials but has met limited success in areas concerning therapy of functional disorders of the brain such as severe depressions but helped prove that disorders of the inhibitory nerve cells play an important role in neuropsychiatric diseases such as schizophrenia.