P 50. Anodal cerebellar tDCS impairs verbal working memory

Abstract

Introduction The cerebellum is not only engaged in sensory-motor function but also cognitive processes like attention and perception (Stoodley and Schmahmann, 2009). The verbal working memory is one of these cognitive processes. Growing evidence suggests that the right cerebellum interacts with Broca's area and left frontal premotor regions during the articulatory control process and contributes to phonological storage (Baddeley, 2003; Paulesu et al., 1993; Desmond et al., 1997). We previously showed that cathodal transcranial direct current stimulation (tDCS) applied to the right cerebellum impairs verbal working memory. We found that cathodal tDCS reduced forward digit spans and blocked practice dependent increase in backward digit span suggesting that the cerebellum contributes to memory recall (Boehringer et al., in press). To address the question on how the right cerebellum contributes to memory recognition we here used cathodal and anodal tDCS before subjects participated in the Sternberg item recognition task. Methods We used a sham-controlled, randomized, blind, crossover design. We investigated 19 young healthy right-handed subjects (age=26±4years, 10 females). Cathodal, anodal or sham tDCS was applied over the right cerebellum with 2mA for 25min. For the Sternberg task subjects were listening to a set of digits. After a break of 7s subjects were listening to the target digit and decided whether the target digit occurred in the set of digits or not. The task was specifically adapted to the individual memory capacities with three different memory load levels (i.e., easy, medium, hard). Results We found impaired item recognition after anodal tDCS ( p =.008). This effect was only present on the medium memory load level while for the easy or hard condition we found no such influence. For cathodal tDCS we found no significant influence on item recognition for any of the three memory load levels. Discussion We found impaired item recognition after anodal tDCS. This effect was only present in the medium memory load level. This suggests that the cerebellum is only involved if individuals are moderately engaged in verbal memory, but not when the memory load is too low or too high. This findings extends previous observations of the involvement of the cerebellum in verbal working memory and suggest that the cerebellum is not generally involved in recognition but for specific demands (Pope and Miall, 2012). Here anodal tDCS may impair the cerebellar output to the PFC. These results extend our previous tDCS study (Boehringer et al., in press) and suggests that the cerebellum contributes not only to memory recall but also to recognition.