Methode und Mechanismen der transkraniellen Gleichstromstimulation

Zusammenfassung

Schwacher Gleichstrom induziert neuroplastische Veränderungen der Erregbarkeit des Kortex von Tier und Mensch. Die Erregbarkeitsveränderungen sind abhängig von der Polarität und der Dauer der Gleichstromstimulation sowie von der verwendeten Stromstärke. Die ursprünglich auf tierexperimentelle Untersuchungen aus den 50er und 60er Jahren zurückgehende Technik, konnte in jüngeren Studien erfolgreich auf die Anwendung am humanen Kortex übertragen werden. Hierbei führt kathodale transkranielle Gleichstromstimulation (tDCS) zu einer Verminderung und anodale Stimulation zu einer Erhöhung der mittels transkranieller Magnetstimulation (TMS) gemessenen kortikalen Erregbarkeit. Abhängig von der Stimulationsdauer können die Effekte jeweils bis zu einer Stunde nach Ende der Stimulation anhalten. Pharmakologische Humanstudien, die tDCS jeweils mit einer Prämedikation des Natriumkanal-Blockers Carbamazepin und des NMDA-Rezeptor-Antagonisten Dextromethorphan kombinierten, legen nahe, dass die Effekte auf eine polaritätsspezifische Verschiebung der Ruhemembranpotenzials zurückgehen, die dann zu einer NMDA-Rezeptor-vermittelten Transformation der synaptischen Stärke führt. Die Mechanismen der tDCS weisen somit eine gewisse Nähe zu bekannten neuroplastischen Phänomenen wie LTP und LTD auf. Hinsichtlich des therapeutischen Potenzials der tDCS konnten bisherige Pilotstudien positive Effekte der anodalen tDCS bei Patienten mit chronischem Schmerzsyndrom, Schlaganfall oder Depression nachweisen. Darüber hinaus begründen sowohl tierexperimentelle Daten als auch eine klinische Pilotstudie die Annahme, dass kathodale tDCS eine mögliche therapeutische Option bei pharmakoresistenten fokalen Epilepsien darstellt, insbesondere bei solchen mit oberflächennahen Foci, wie sie beispielsweise bei der Epilepsia partials continua oder bei kortikalen Dysplasien auftreten. Bevor die Ergebnisse zur therapeutischen Wirkung der jüngsten Pilotstudien zu einem breiteren klinischen Einsatz der tDCS bei Patienten mit Epilepsie, Schlaganfall oder Depression führen, sollten Untersuchungen zur Optimierung der Effektivität und Stabilität der erzeugten neuroplastischen Effekte z. B. durch Intensivierung der tDCS-Protokolle durchgeführt werden.

Abstract

Weak direct current stimulation induces neuroplastic changes of cortical excitability in animals and humans. The effects depend on polarity and duration of the direct current stimulation as well as on the applied current strength. Originally based on animal experiments of the 1950s and 1960s, the technique of transcranial direct current stimulation (tDCS) has recently been successfully transferred to the human motor cortex. Here, cathodal tDCS results in a decreased cortical excitability whereas the anodal form leads to an enhancement of TMS-assessed cortical excitability. Depending on the stimulation duration, after-effects can be achieved that last up to one hour. Pharmacological studies, which combined tDCS with a premedication of the Na channel-blocking carbamazepine and the NMDA receptor antagonist dextromethorphan, demonstrate that the after-effects of tDCS involve polarity-specific shifts of membrane potentials and a consecutive NMDA receptor-mediated transformation of synaptic strength. Therefore, the mechanisms of tDCS after-effects share similarities with those of the well-known neuroplastic effects of LTP and LTD. With respect to the therapeutic potential of tDCS, pilot studies suggest positive effects of anodal tDCS in patients with chronic pain, chronic stroke and major depression. For cathodal tDCS, recent animal and clinical studies demonstrated antiepileptic properties, supporting the hypothesis that cathodal tDCS might serve as a therapeutic option in drug-refractory focal epilepsy, particular in cases with superficial foci as in patients with epilepsia partialis continua or cortical dysplasia. Before these piloting results of beneficial tDCS effects can be transformed into a broader therapeutic application of tDCS in patients with epilepsy, chronic stroke or major depression, further research should optimize the power and stability of the induced neuroplastic effects.

Schlüsselwörter

Transkranielle Gleichstromstimulation (tDCS) - Transkranielle Magnetstimulation (TMS) - Neuroplastizität

Key words

Transcranial direct current stimulation (tDCS) - Transcranial magnetic stimulation (TMS) - Neuroplasicity

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