P 95. Acquisition of conditioned eyeblink responses is modulated by cerebellar tDCS

Abstract

Background Classical conditioning of the eyeblink reflex is a simple form of motor learning which depends on the integrity of the cerebellum. Acquistion of conditioned eyeblink responses is markedly impaired in patients with cerebellar disorders. Noninvasive transcranial direct current stimulation (tDCS) has been reported to modify the excitability of the cerebellum (Galea et al., 2009, 2010). The aim of the study was to assess whether acquisition of conditioned eyeblink responses (CRs) is modulated by cerebellar tDCS. Methods A standard delay conditioning paradigm (a 540 ms tone-CS coterminating with a 100 ms air-puff-US, 100 paired CS-US trials and 30 extinction CS-alone trials) was used in a total of 30 healthy subjects (18 f, 12 m, mean age 23.4 ± 1.9 years). TDCS (2 mA intensity, ramp like onset) was applied over the right cerebellar hemisphere ipsilaterally to the US. TDCS was applied during the acquisition phase. Subjects were randomly assigned to 3 groups (n = 10) using anodal, cathodal or sham stimulation. The investigator as well as the participants was blinded to the stimulation modality. Results Compared to sham stimulation mean CR-incidence and learning rate were significantly enhanced by anodal tDCS, whereas onset of CRs occurred significantly earlier. Mean CR incidence and learning rate were significantly reduced in the cathodal stimulation group with no significant changes of timing compared to sham stimulation. Conclusions In healthy individuals anodal cerebellar tDCS appears to enhance the ability to acquire conditioned eyeblink responses which, however, were less appropriately timed. On the contrary CR-acquisition was markedly decreased by cathodal stimulation.