Utilising TMS-EEG to Assess the Response to Cerebellar-Brain Inhibition

Area of Science:

• Neuroscience
• Neurophysiology
• Brain Stimulation

Background:

• Cerebellar-brain inhibition (CBI) assesses cerebellar pathways to the motor cortex using transcranial magnetic stimulation (TMS).
• Current CBI methods can be uncomfortable, necessitating alternative approaches for evaluating cerebellum-cortex connectivity.
• TMS-evoked electroencephalography potentials (TEPs) offer a potential non-invasive measure of cortical excitability.

Purpose of the Study:

• To investigate the utility of combined TMS-EEG for measuring responses to CBI.
• To compare the effects of different TMS coil types (figure-of-eight and double cone) on TEPs during CBI.
• To determine if TMS-EEG can differentiate true CBI from sham stimulation.

Main Methods:

• Thirty-three healthy volunteers participated in three experiments.
• Experiment 1: CBI induced with a figure-of-eight coil over the cerebellum, followed by TMS to the motor cortex and EEG recording.
• Experiment 2: CBI induced with a double cone coil over the cerebellum, followed by TMS to the motor cortex and EEG recording.
• Experiment 3: Multisensory sham stimulation control condition.

Main Results:

• Both figure-of-eight and double cone coils significantly suppressed early TEPs elicited by motor cortex TMS.
• The TEP changes correlated with motor inhibitory effects of CBI when using the double cone coil.
• Sham stimulation did not alter the TEPs, indicating specificity of the observed effects.

Conclusions:

• Combined TMS-EEG can successfully index CBI responses, providing a potential alternative to uncomfortable traditional methods.
• Both tested coil types appear to engage cerebellar projections, though potentially through different mechanisms.
• TMS-EEG offers a valuable tool for studying cerebellum-motor cortex interactions non-invasively.