Far Field Effects of Cortical tDCS in the Cerebellum may Contribute to its Effects on Learning.

In previous studies, we have used imaging and tDCS to examine the brain basis of learning to detect objects hidden in a complex visual environment. Learning this task resulted in increased activity in right lateral frontal and parietal cortices, and reduced activity in occipital-temporal regions bilaterally. We hypothesized that anodal and cathodal stimulation over regions showing increased and decreased activity with learning, respectively, would both result in increased performance. In agreement with this, we found that both anodal F10 or P4 vs. cathodal contralateral arm stimulation (Clark et al., 2012; Coffman et al. 2012; Falcone et al. 2012), and cathodal T5 vs. anodal left arm stimulation were associated with increased performance (Clark et al., 2013). However, F10 anode vs. T5 cathode did not result in significantly increased performance. Modeling of these showed that the effective protocols using scalp vs. left arm electrodes produced effects in the cerebellum (with opposite polarities), but the ineffective protocol (F10 anode vs. T5 cathode) did not. Therefore, it's possible that the observed effects of tDCS on learning might have resulted from an effect of stimulation on the cerebellum, rather than an effect on cortex, or a combination of cerebellum and cortex. Cerebellar stimulation has previously been used to modulate motor control, cognition, learning, and aff5ct (Ferrucci et. al., 2013), all of which might influence performance on this task. We are currently planning studies to compare the effects of cerebellar vs. cortical stimulation on learning and performance of this task.