# Effects of Cerebellar Transcranial Direct Current Stimulation on Cerebellar Brain Inhibition as a Function of TMS Coil Orientation

## TL;DR

This study shows that cerebellar stimulation affects brain inhibition differently depending on the direction of the magnetic coil used.

## Contribution

The study reveals that cerebellar stimulation's effect on brain inhibition depends on TMS coil orientation, with AP orientation being more sensitive.

## Key findings

- Anodal ctDCS increased cerebellar brain inhibition (CBI) for the anterior-posterior (AP) coil orientation.
- CBI measured with AP coil orientation (CBI-AP-7) is more sensitive to ctDCS effects than posterior-anterior (PA) orientation.
- Cerebellar stimulation had no significant effect on CBI for the posterior-anterior (PA) coil orientation.

## Abstract

Cerebellar brain inhibition (CBI) is a way to quantify the cerebellar influence on the motor cortex in humans. Studies suggest that the orientation of the transcranial magnetic stimulation (TMS) coil influences which motor networks are activated.

This study investigated the influence of cerebellar transcranial direct current stimulation (ctDCS) on CBI as a function of coil orientation (anterior–posterior [AP] vs. posterior–anterior [PA]). An interstimulus interval (ISI) of 7 ms (CBI‐AP‐7) was used for AP orientation and 5 ms (CBI‐PA‐5) for PA orientation.

Young and healthy participants received anodal, cathodal, or sham ctDCS treatment for 15 min on three different days. On each day, CBI was determined for both coil positions immediately after and 30, 60, and 120 min after ctDCS application.

For CBI‐PA‐5, no significant ctDCS effect was detected. For CBI‐AP‐7, there was an increase in CBI by anodal ctDCS and a decrease in CBI by cathodal ctDCS, although the latter did not reach statistical significance.

Findings provide further support that different cerebello–cerebral motor networks may be activated in CBI‐AP‐7 and CBI‐PA‐5, with only CBI‐AP‐7 being significantly affected by ctDCS. CBI‐AP‐7 may be a more sensitive tool for investigating CBI effects than the CBI‐PA‐5 procedure, which is most commonly used.

The impact of cerebellar direct current stimulation (ctDCS) on cerebellar brain inhibition (CBI) as a function of TMS coil orientation was investigated. Anodal ctDCS led to an increase in CBI for the anterior‐posterior (AP) orientation only. These results implicate, that different motor networks may be activated depending on the coil orientation and that CBI‐AP‐7 (CBI measured with AP position of the TMS coil and an interstimulus interval of 7 ms) may be a more sensitive tool for investigating CBI effects.