Klinische Neurophysiologie 2010; 41 - ID155
DOI: 10.1055/s-0030-1250984

Boosting brain excitability by transcranial high frequency stimulation in the ripple range

V Moliadze 1, A Antal 1, W Paulus 1
  • 1Georg-August Universität Göttingen, Klinische Neurophysiologie, Göttingen, Deutschland

Introduction: High frequency neuronal oscillations in the range of 80–250Hz, termed the 'ripple range', play a key role both in normal and abnormal brain functions such as epilepsy. The concept described here is an attempt to modulate neuronal excitability by high frequency transcranial alternating current stimulation (tACS) in the ripple range, in a frequency-dependent fashion. Here, for the first time we have tested the effects of 80, 140 and 250Hz oscillations on motor evoked potential (MEP) amplitude

Methods: Altogether 12 subjects participated in the experiments. They received on separate days AC- (80Hz, 140Hz, 250Hz,) and sham stimulations in a randomized order. Stimulation was delivered by a battery-driven electrical stimulator (NeuroConn GmbH, Ilmenau, Germany) through conductive-rubber electrodes, placed in two saline-soaked sponges. To detect changes of excitability MEPs of the right first dorsal interosseus muscle (FDI) were recorded during and following stimulation of its motor-cortical representation field by single-pulse transcranial magnetic stimulation (TMS).

For the TMS train during the AC stimulation, the MEPs were subdivided into successive groups of 15, each covering a time range of 1min, and the means for each group were calculated. Following stimulation, 20 single test-pulse MEPs were recorded at, i.e., 0, 5, and 10min after stimulation and then every 10min up to 60min.

Results: Using tACS we could immediately increase motor cortex (M1) excitability as measured by TMS during 140Hz stimulation with an induced aftereffect of 1 hour. Controls by sham and 80Hz stimulation were without any effect. Furthermore, 250Hz was effective only with a delayed induction and reduced duration.

Interestingly, in our study, 140Hz stimulation excitatory after-effects are not sensitive to the physiological state of stimulating neurons.

Conclusions: Targeting of cortical ripples may have the potential to manipulate human cognitive functions and to further extend research in the therapeutic application of non-invasive rhythmic brain stimulation.