Frequency-dependent modulation of cerebellar excitability during the application of non-invasive alternating current stimulation

Danny Spampinato,Esin Avci,John Rothwell,Lorenzo Rocchi

doi:10.1016/j.brs.2021.01.007

Danny Spampinato, Esin Avci + Show 2 more

Open Access

https://doi.org/10.1016/j.brs.2021.01.007

Copy DOI

Abstract

Backgroundit is well-known that the cerebellum is critical for the integrity of motor and cognitive actions. Applying non-invasive brain stimulation techniques over this region results in neurophysiological and behavioural changes, which have been associated with the modulation of cerebellar-cerebral cortex connectivity. Here, we investigated whether online application of cerebellar transcranial alternating current stimulation (tACS) results in changes to this pathway. Methodsthirteen healthy individuals participated in two sessions of cerebellar tACS delivered at different frequencies (5Hz and 50Hz). We used transcranial magnetic stimulation to measure cerebellar-motor cortex (M1) inhibition (CBI), short-intracortical inhibition (SICI) and short-afferent inhibition (SAI) before, during and after the application of tACS. Resultswe found that CBI was specifically strengthened during the application of 5Hz cerebellar tACS. No changes were detected immediately following the application of 5Hz stimulation, nor at any time point with 50Hz stimulation. We also found no changes to M1 intracortical circuits (i.e. SICI) or sensorimotor interaction (i.e. SAI), indicating that the effects of 5Hz tACS over the cerebellum are site-specific. Conclusionscerebellar tACS can modulate cerebellar excitability in a time- and frequency-dependent manner. Additionally, cerebellar tACS does not appear to induce any long-lasting effects (i.e. plasticity), suggesting that stimulation enhances oscillations within the cerebellum only throughout the stimulation period. As such, cerebellar tACS may have significant implications for diseases manifesting with abnormal cerebellar oscillatory activity and also for future behavioural studies.

Highlights

The cerebellum plays a vital role in the several daily actions humans perform, including adapting and fine-tuning of movements [1], as well as in performing behaviours with cognitive demands [2,3]
cortex (M1) inhibition (CBI) changes only occur during 5Hz cerebellar transcranial alternating current stimulation (tACS)
When we compared CBI prior to, during and after the application of cerebellar tACS, we found variable changes depending on the frequency selected

Summary

Introduction

The cerebellum plays a vital role in the several daily actions humans perform, including adapting and fine-tuning of movements [1], as well as in performing behaviours with cognitive demands [2,3]. There are inconsistencies in terms of both the magnitude and direction of effects with these approaches [19,20]. This is most likely due to the substantial interindividual variability and lack of neural predictors in response to brain stimulation. In part, this is explained by the limited range in which stimulation can target the cerebellum [21], including where stimulation should be applied (e.g. location of figure-eight TMS coil) and which montage should be selected (e.g. polar-dependency of tDCS)

Methods

Results

Discussion

Conclusion