Gamma tACS over M1 and cerebellar hemisphere improves motor performance in a phase-specific manner

Non-Invasive Cerebellar Stimulation in Neurodegenerative Ataxia: A Literature Review

“…Moreover, transcranial alternating current stimulation (tACS) also has recently emerged as a new technique to modulate cortical oscillations and entrain brain rhythms in specific frequencies [101]. By applying cerebellar tACS at a frequency matching the basal firing rate of Purkinje cells (50 Hz), researchers have shown that tACS may modulate CBI and improve the performance of a motor tasks in healthy controls [102][103][104][105][106]. Whether these novel types of stimulation might be effective also in the treatment of cerebellar ataxias is still unknown.…”

“…Critically, evaluation of target engagement using imaging or physiologic biomarkers, as well as the assessment of "dose" by using modelling to calculate the induced currents in the brain to define individual stimulation parameters, would be essential. Moreover, the cerebellum can show significant structural changes in term of climbing fiber Purkinje cell and parallel fiber Purkinje cell wirings in cerebellar ataxia and other disorders [102][103][104][105][106], and some wiring features can be rapidly changed within days and affect cerebellar synchronization [107]. These structural changes may affect the effect of TMS and tDCS, and should be considered future studies.…”

Oscillating neural networks: perspectives from rhythmic brain stimulation

“…However, the tACS current output can be split into many sites of stimulation, resulting in 0° and 180° phase-lags (see Figure 1.9 for some examples). Broadly, anti-phase relationships are thought to decouple network nodes (down-regulating coherence, Helfrich et al, 2014a;Polanía et al, 2015), whereas in-phase relationships are thought to couple the targeted structures (increasing functional cooperation; Polanía et al, 2012), though with exceptions (e.g., Strüber et al, 2014;Tseng et al, 2016;Miyaguchi et al, 2019). Targeting phase relationships across neural networks with multi-electrode arrays.…”

“…Multi-electrode tACS montages have been used to couple and decouple structures in the same cerebral hemisphere (e.g., left frontoparietal network, Polanía et al, 2012;Hu et al, 2018; right frontoparietal network, Violante et al, 2017;van Schouwenburg et al, 2018;left temporoparietal network, Tseng et al, 2016) or between cerebral hemispheres (e.g., bilateral parietooccipital cortices, Helfrich et al, 2014a;Strüber et al, 2014;Bland et al, 2018;bilateral motor cortices, Bächinger et al, 2017;Heise et al, 2017; left motor cortex and right cerebellum, Miyaguchi et al, 2019). Intrahemispheric networks can even be coupled and decoupled bilaterally (e.g., Polanía et al, 2015;Alekseichuk et al, 2017).…”

“…Anti-phase tACS either led to interhemispheric coupling with a consistent 180°-lag (i.e., increased coherence, Strüber et al, 2014; remembering that MSC does not consider the phase-lag) or to decoupling with no consistent phase relationship (i.e., decreased coherence, Helfrich et al, 2014a). Clearly, increased coherence does not always reflect increased functional cooperation, and anti-phase tACS does not always decrease coherence-with some evidence that the latter can actually foster functional cooperation (even with a 180° offset; e.g., Tseng et al, 2016;Miyaguchi et al, 2019). This makes sense given that neural communication is not instantaneous, with greater phase-lags expected over longer distances or with higher frequencies (see section 1.3.2).…”