AUTHOR COPY Restorative Neurology and Neuroscience 30 (2012) 255–263 DOI 10.3233/RNN-2012-110208 IOS Press 255 Cathodal stimulation of human MT+ leads to elevated fMRI signal: A tDCS-fMRI study Andrea Antal a,1,∗ , Gyula Kov´ acs b,c,1 , Leila Chaieb a , Csaba Cziraki b,c , Walter Paulus a and Mark W. Greenlee b a Department of Clinical Neurophysiology, University Medical Center, Georg-August University of G¨ ottingen, G¨ ottingen, Germany b Institute of Psychology, University of Regensburg, Regensburg, Germany c Department of Cognitive Science, Budapest University of Technology and Economics, Budapest, Hungary Abstract. Purpose: Transcranial direct current stimulation (tDCS) was reintroduced about a decade ago as a tool for inducing long-lasting changes in cortical excitability. Recently it has been shown that both motor and cognitive functions can be influenced by tDCS. Here, we tested the effect of tDCS on the blood-oxygen level dependent (BOLD) signal evoked by coherent visual motion using functional magnetic resonance imaging (fMRI). Methods: The subjects underwent 10 min of cathodal and sham tDCS, applied over the right MT+. Following stimulation, random dot kinomatograms (RDK) with different percentages (10%, 30%, 50%) of coherently moving dots were presented. Results: All motion stimuli activated MT+ in both stimulation conditions. However, cathodal stimulation led to an increase in fMRI signal in MT+ when compared to sham stimulation. This effect did not depend on the coherence level of the visual stimulus. Conclusions: Here, we show for the first time, that cathodal tDCS stimulation leads to elevated fMRI signal in the human visual cortex. Keywords: Area MT+, fMRI, motion perception, transcranial direct current stimulation (tDCS) 1. Introduction Currently non-invasive external stimulation tech- niques such as transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) have become popular tools in research of human brain functions (for reviews see: Cowey and Walsh, 2001; Fregni and Pascual-Leone, 2007; Nitsche et al., 2008, Antal et al., 2011; Nitsche and Paulus, 2011, Song et al., 2011). TMS generates a strong magnetic impulse that is able to induce an electric field within the cortex and elicit action potentials. 1 These authors contributed equally. ∗ Corresponding author: Andrea Antal, PhD, Department of Clin- ical Neurophysiology, Georg-August University of G¨ ottingen, 37075 G¨ ottingen, Robert Koch Straße 40, Germany, Tel.: +49 551 398461; Fax: +49 551 398126; E-mail: Aantal@gwdg.de. The net effect is a transient interruption of normal brain activity and corresponding behavioral impair- ments have been demonstrated in various motor and cognitive tasks (e.g., Sack et al., 2007). In contrast to this, tDCS represents the other end of the stim- ulation spectrum by delivering a continuous electric current. In early animal studies it was shown that apply- ing anodal tDCS to the surface of both the motor and the visual cortex increases cortical excitability, prob- ably by depolarizing neuronal membranes, and thus increasing the spontaneous firing rate of the cells, whilst a cathodal current results in the reverse effect, most likely due to a hyperpolarizing effect (Creutzfeld et al., 1962). In humans the induced after-effects depended on the polarity, the duration and intensity of the stimulation (Nitsche and Paulus, 2000, 2001). In particular, measuring the amplitude of motor evoked 0922-6028/12/$27.50 © 2012 – IOS Press and the authors. All rights reserved