Anodal Transcranial Direct Current Stimulation (tDCS) Decreases the Amplitudes of Long-Latency Stretch Reflexes in Cerebellar Ataxia

Recent studies suggest that the neuromodulation of the cerebellum using transcranial direct current stimulation (tDCS) could represent a new therapeutic strategy for the management of cerebellar disorders. Anodal tDCS of the cerebellum increases the excitability of the cerebellar cortex. We tested the effects of anodal tDCS applied over the cerebellum in ataxic patients. We studied (a) stretch reflexes (SR) in upper limb (SLSR: short-latency stretch reflexes; LLSR: long-latency stretch reflexes), (b) a coordination functional task in upper limbs based on mechanical counters (MCT: mechanical counter test), and (c) computerized posturography. tDCS did not change the amplitude of SLSR, but reduced significantly the amplitudes of LLSR. tDCS did not improve the MCT scores and did not modify posture. We suggest that anodal tDCS of the cerebellum reduces the amplitudes of LLSR by increasing the inhibitory effect exerted by the cerebellar cortex upon cerebellar nuclei. The absence of effect upon upper limb coordination and posture suggests that the cerebello-cerebral networks subserving these functions are less responsive to anodal tDCS of the cerebellum. Anodal tDCS of the cerebellum represents a novel experimental tool to investigate the effects of the cerebellar cortex on the modulation of the amplitudes of LLSR.