Modelling the electric field and the current density generated by cerebellar transcranial DC stimulation in humans
Introduction
Transcranial Direct Current Stimulation (tDCS) is a non-invasive technique that modulates brain excitability (Priori, 2003, Nitsche and Paulus, 2011, Brunoni et al., 2012). tDCS over the cerebellum (or cerebellar tDCS) influences working memory (Ferrucci et al., 2008) and the processing of negative facial emotion (Ferrucci et al., 2012), motor control (Jayaram et al., 2012), and cerebello-cerebral connections (Galea et al., 2009) in healthy subjects. Cerebellar tDCS has also been recently proposed for the treatment of cerebellar disorders (Manto, 2008).
Among the open issues concerning cerebellar tDCS, the electric current density (J) and the electric field (E) that cross the skull and reach the cerebellum remain unknown. We therefore aimed to evaluate the electric quantities induced within the skull by cerebellar tDCS by using computational electromagnetic techniques on three realistic human models (of different age and sex), allowing to analyze current flow through the brain, the cerebellum and the brainstem. This could be of some help particularly in the investigation about the possible involvement of the cerebral cortex during cerebellar stimulation. Moreover, this study could provide answer to possible concerns about the safety of this tDCS application, providing information about the electric field in the brainstem and the heart.
Section snippets
Methods
Simulations were conducted using the simulation platform SEMCAD X (by SPEAG, Schmid & Partner Engineering, AG, Zurich, Switzerland, www.speag.com), solving the Laplace equation to determine the electric potential (φ) distribution inside the human tissueswhere σ is the electrical conductivity of the human tissues. The E and J field distributions were obtained by means of the following relations:
Three human realistic models of the Virtual Family (Christ et al., 2010) were used.
Results
The higher J-field amplitudes generated by cerebellar tDCS were near the active electrode in the cerebellum at cortical level within the posterior lobe (Fig. 2). The J spread over the occipital cortex – quantified as the percentage of occipital volume where the amplitude of J-field is greater than 70% of the peak of J in the cerebellum – was only 4% for “Duke” and much less than 1% for “Ella” and “Billie”. The J slightly spreads also to the more anterior area of the cerebellum, particularly in
Discussions and conclusions
We here reported the first modeling study on the electric field generated by transcutaneous cerebellar DC stimulation in humans. Despite some inter-individual differences, cerebellar tDCS generates the highest electric field and current density below the stimulating electrode in the posterior cerebellum with a slight spread to other structures (Fig. 2). Within the cerebellum the current density distribution varies across different subjects, being maximum toward the more anterior part in the
Financial disclosures
Prof. Alberto Priori and Dr. Roberta Ferrucci reports no financial interests or potential conflicts of interests; Roberta Ferrucci and Alberto Priori are stakeholders of Newronika s.r.l., a spin-off company of the Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico and of the Università degli Studi di Milano.
Acknowledgment
The authors wish to thank Schmid & Partner Engineering AG (www.speag.com) for having provided the simulation software SEMCAD X.
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