tDCS of the Cerebellum: Where Do We Stand in 2016? Technical Issues and Critical Review of the Literature

Abstract

Transcranial Direct Current Stimulation (tDCS) is an up-and-coming electrical neurostimulation technique increasingly used both in healthy subjects and in selected groups of patients. Due to the high density of neurons in the cerebellum, its peculiar anatomical organization with the cortex lying superficially below the skull and its diffuse connections with motor and associative areas of the cerebrum, the cerebellum is becoming a major target for neuromodulation of the cerebellocerebral networks. We discuss the recent studies based on cerebellar tDCS with a focus on the numerous technical and open issues which remain to be solved. Our current knowledge of the physiological impacts of tDCS on cerebellar circuitry is criticized. We provide a comparison with transcranial Alternating Current Stimulation (tACS), another promising transcranial electrical neurostimulation technique. Although both tDCS and tACS are becoming established techniques to modulate the cerebellocerebral networks, it is surprising that their impacts on cerebellar disorders remains unclear. A major reason is that the literature lacks large trials with a double-blind, sham-controlled, and cross-over experimental design in cerebellar patients.

Transcranial Cerebellar Direct Current Stimulation Enhances Verb Generation but Not Verb Naming in Poststroke Aphasia

“…It has been proposed that cerebellar tDCS is most likely to produce its effects by polarizing Purkinje cells (see Pope & Miall, 2014;van Dun, Bodranghien, Mariën, & Manto, 2016) and changing the levels/pattern of activity in the deep cerebellar output nuclei, thereby also affecting distant plasticity in human cortical areas (Grimaldi et al, 2016;van Dun et al, 2016). Indeed, it has been shown that, while anodal stimulation, through its excitatory effects, increases the discharge from the Purkinje cells, augmenting the inhibition of the facilitatory pathways from the cerebellar nuclei to the cerebral cortex; cathodal stimulation exerts the opposite F o r R e v i e w O n l y or sham tDCS over the right cerebellum.…”

A computational pipeline to determine lobular electric field distribution during cerebellar transcranial direct current stimulation

“…Marr-Albus-Ito hypothesis is the earliest and most studied mechanism that is based on the architecture of the cerebellar cortex and assigns specific functions to the climbing fiber-Purkinje cell and the mossy fiber-granule cell-parallel fiber-Purkinje cell circuits (Popa et al, 2016). A significant concentration of neurons in cerebellum is due to densely packed small granule cells (van Dun et al, 2016) that can support matrix memory based on Hebbian learning primarily for 'readout tables'. Cerebellum has an essential role in motor learning and coordination as well as non-motor functions such as sensory and cognitive processes (Buckner, 2013).…”

“…Here, neuroplasticity can be facilitated with an extrinsic stimuli using noninvasive brain stimulation (NIBS) (Hallett, 2005), which has been shown recently to modulate brain (Shafi et al, 2012) and spinal (Wolpaw, 2010) network interactions. Specifically, Purkinje cell firing has several of the characteristics of a forward internal model (Ebner, 2013) which is the main target of cerebellar transcranial direct current stimulation (ctDCS) (Galea et al, 2009) -a painless non-invasive technique where a weak direct current (i.e., up to 2mA) is delivered through a scalp electrode overlying the cerebellum (van Dun et al, 2016).…”

Non-invasive Cerebellar Stimulation: Moving Towards Clinical Applications for Cerebellar and Extra-Cerebellar Disorders

“…Due to its numerous connections with the motor and associative cortical regions, its high density of neurons (in particular in the cerebellar cortex), its electrical properties, and its position immediately below the skull, the cerebellum is now considered as a real target to modulate distant cortical regions [9,10].…”