Cerebellar tDCS Does Not Enhance Performance in an Implicit Categorization Learning Task

Abstract

Background: Transcranial Direct Current Stimulation (tDCS) is a form of non-invasive electrical stimulation that changes neuronal excitability in a polarity and site-specific manner. In cognitive tasks related to prefrontal and cerebellar learning, cortical tDCS arguably facilitates learning, but the few studies investigating cerebellar tDCS, however, are inconsistent.Objective: We investigate the effect of cerebellar tDCS on performance of an implicit categorization learning task.Methods: Forty participants performed a computerized version of an implicit categorization learning task where squares had to be sorted into two categories, according to an unknown but fixed rule that integrated both the size and luminance of the square. Participants did one round of categorization to familiarize themselves with the task and to provide a baseline of performance. After that, 20 participants received anodal tDCS (20 min, 1.5 mA) over the right cerebellum, and 19 participants received sham stimulation and simultaneously started a second session of the categorization task using a new rule.Results: As expected, subjects performed better in the second session than in the first, baseline session, showing increased accuracy scores and reduced reaction times. Over trials, participants learned the categorization rule, improving their accuracy and reaction times. However, we observed no effect of anodal tDCS stimulation on overall performance or on learning, compared to sham stimulation.Conclusion: These results suggest that cerebellar tDCS does not modulate performance and learning on an implicit categorization task.

Targeting the Human Cerebellum with Transcranial Direct Current Stimulation to Modulate Behavior: a Meta-Analysis

“…Table 1 shows an overview of the main characteristics of the selected studies. Of these 32 studies, 15 studies applied both anodal and cathodal stimulation (ID: 4, 10, 14, 19, 21, 22, 24, 27, 28, 29, 31, and 32) [ 17 , 23 , 27 , 30 , 32 , 34 – 36 , 39 – 41 , 43 , 44 ], 14 anodal (ID 1, 5, 6, 7, 8, 11, 12, 13, 15, 16, 18, 20, 23, and 30) [ 14 , 18 – 21 , 24 – 26 , 29 , 31 , 33 , 42 , 45 ], and three cathodal tDCS (ID: 3, 9, and 26) [ 16 , 22 , 38 ] (Table 1 ). In study 2 [ 15 ] were reported three experiments, each one comparing anodal and cathodal stimulation.…”

Consensus Paper: Experimental Neurostimulation of the Cerebellum

“…Several preliminary studies have reported positive effects of anodal ctDCS on verbal fluency [286] and pain perception [287] in healthy subjects and cognitive symptoms in Parkinson’s patients [217]. While other studies have observed no effect on cognitive learning [288] or memory [289], for example. A meta-analysis of cognition studies found cognitive processes were influenced by anodal ctDCS but to a lesser extent than motor-related effects [290].…”

Entrainment of cerebellar purkinje cells with directional AC electric fields in anesthetized rats

“…Indeed, tES has been found to have beneficial effects when applied to a number of different brain areas, including specific regions of the cerebral and cerebellar cortices [6,7]. Although such positive reports highlight the potential of tES, other studies have shown no results or negative ones [8,9]. The causes of this variability need to be understood in order for tES to reach its potential.…”