Non-invasive cerebellar stimulation to rearrange disrupted functional networks

Abstract

Non-invasive brain stimulation (NIBS) is a promising technique that has been proven to modify neural excitability using electric current (transcranial electric current, TES) or magnetic pulses (transcranial magnetic stimulation, TMS) (Janssen, Oostendorp, & Stegeman, 2015; Woods et al., 2016). Most research focused on stimulating the area directly beneath the electrodes or the coil to directly facilitate or inhibit the functioning of that area (e.g. motor cortex stimulation). Recently, a different strategy has been introduced in NIBS research, focusing on the cerebellum as a window upon functional connectivity networks (van Dun, Bodranghien, Manto, & Mariën, 2017). Indeed, the cerebellum is strongly connected to the motor and associative regions of the cerebrum via closed loops running in parallel, allowing communication in both directions. In addition, the cerebellum has the highest density of neurons and has a dense cortical cellularity, making it very susceptible to NIBS (van Dun & Manto, 2018; van Dun, Overwalle, Manto, & Marien, 2018). EEG studies using cerebellar TMS have shown that cerebellar stimulation induces activity in the contralateral cerebral hemisphere that spreads towards the bilateral prefrontal cortices and to the ipsilateral cerebral hemisphere within 40ms (Arimatsu, Sato, Ge, Ueno, & Iramina, 2007; Iramina, Maeno, Kowatari, & Ueno, 2002; Iramina, Maeno, Nonaka, & Ueno, 2003; Iramina, Maeno, & Ueno, 2004; Iwahashi et al., 2009). In addition, studies using cerebellar TES showed altered excitatory and inhibitory cortico-cortical and cerebello-cortical networks (e.g. Chothia, Doeltgen, & Bradnam, 2016; Galea, Jayaram, Ajagbe, & Celnik, 2009). Modulating remote functional connectivity via the cerebellum is especially interesting for subcortical lesions. These lesions are not reachable by NIBS but can disturb networks involving several cortical regions. By targeting the cerebellum with NIBS, it might be possible to target the whole disrupted network and regain some connectivity between the affected regions (van Dun et al., 2018). We will present functional MRI (fMRI) and behavioral data of a patient with a left basal ganglia hemorrhagic stroke resulting in hypokinetic dysarthria. Cerebellar stimulation (anode over left, cathode over right cerebellar hemisphere) was applied during language therapy. fMRI was taken before and after an 8-week protocol.