In the first study, we aimed to identify the oscillations supporting the communication between the cerebellum and the cortex and determine whether this dialogue is shaped by their structural connections. To this aim, we combined two cutting-edge techniques already used, independently, for the study of cortical connectivity: transcranial magnetic stimulation concurrent to electroencephalography (TMS-EEG) and diffusion magnetic resonance imaging (dMRI). DMRI is a type of MRI sequence that assesses the local fiber orientations and infers long-range pathways connecting distant regions of the brain (fiber tractography). DMRI has excellent spatial resolution but does not provide any temporal information on brain signalling dynamics. On the other hand, online TMS-EEG allows (via EEG) the measure of changes in brain oscillatory activity either during TMS single-pulses or brief bursts tuned in frequency and phase. By using EEG and its high temporal resolution, one can extract the information on the responses induced by TMS and evaluate the temporal dynamics of connections between brain areas (i.e. cerebellum and the cortex). We have collected the data from n=20 healthy participants who underwent both dMRI and TMS-EEG. Additionally, resting state fMRI datasets were also recorded for each individual. Data analysis is still ongoing, but current preliminary analyses support the tolerability and feasibility of cerebellar TMS-EEG recordings, and our ability to assess signs of communication through oscillations between the cerebellum and the frontal cortex while minimizing unspecific effects (responses triggered by the TMS clicking sound, scalp-tapping, etc).
The second part of my work consisted of addressing two research questions: (1) does pre-movement beta oscillatory activity (20 Hz) reflect the ability of the cerebellar-cortical network to adapt to the changes of the environment? (2) can we enhance motor adaptation by entraining cerebellar oscillations? In the first study, we analysed the data of 17 healthy participants performing a visuomotor adaptation task while their brain oscillatory activity was recorded with magnetoencephalography (MEG). We aimed to characterize pre-movement oscillatory related to the adaptation to visual biases. Preliminary results show a modulation of anticipatory beta activity (20 Hz) based on motor adjustments due to the bias, localized in a network including the right cerebellum (crus II), the left parietal inferior lobule and the right frontal inferior lobe. Finally, I also collaborated on a second study in which we analysed data from 16 Writer’s Cramp (WC) dystonic patients and age- and gender-matched healthy controls who performed the visuomotor task during MEG recordings. Here, we aimed at determining whether cerebellar oscillations related to motor adaptation are affected in WC patients. Furthermore, we wanted to determine whether it is possible to boost motor adaptation by driving cerebellar oscillations with transcranial alternating current stimulation (tACS). Transcranial ACS is an electrical non-invasive stimulation technique that can entrain brain oscillations and modulate motor performance. Our results show that anticipatory cerebellar activity in WC patients, compared to healthy controls, was normal at beta frequency but abnormal at gamma frequency, which was also related to aberrant adaptation. Furthermore, tACS (but not placebo stimulation) was able to compensate for cerebellar gamma dysrhythmia and increase patients’ learning performance via modulation of a thalamic relay. The findings of the second study are currently being submitted for publication.
The results of this project have been presented at 2 national and 3 international conferences (1 poster award). One study is being prepared for submission to a top-tier journal and one abstract has been published.
