Abstract
Damage to the vestibular cerebellum results in dysfunctional standing posture control. Patients with cerebellum dysfunction have a larger sway in the center of gravity while standing compared with healthy subjects. Transcranial direct current stimulation (tDCS) is a noninvasive technique for selectively exciting or inhibiting specific neural structures with potential applications in functional assessment and treatment of neural disorders. However, the specific stimulation parameters for influencing postural control have not been assessed. In this study, we investigated the influence of tDCS when applied over the cerebellum on standing posture control. Sixteen healthy subjects received tDCS (20 min, 2 mA) over the scalp 2 cm below the inion. In Experiment 1, all 16 subjects received tDCS under three stimulus conditions, Sham, Cathodal, and Anodal, in a random order with the second electrode placed on the forehead. In Experiment 2, five subjects received cathodal stimulation only with the second electrode placed over the right buccinator muscle. Center of gravity sway was measured twice for 60 s before and after tDCS in a standing posture with eyes open and legs closed, and average total locus length, locus length per second, rectangular area, and enveloped area were calculated. In Experiment 1, total locus length and locus length per second decreased significantly after cathodal stimulation but not after anodal or sham stimulation, while no tDCS condition influenced rectangular or enveloped areas. In Experiment 2, cathodal tDCS again significantly reduced total locus length and locus length per second but not rectangular and enveloped areas. The effects of tDCS on postural control are polarity-dependent, likely reflecting the selective excitation or inhibition of cerebellar Purkinje cells. Cathodal tDCS to the cerebellum of healthy subjects can alter body sway (velocity).
Highlights
Human balance is controlled by vestibular, visual, and somatosensory inputs to the brainstem and vestibular cerebellum (Peterka and Loughlin, 2004)
We demonstrate that cathodal Transcranial direct current stimulation (tDCS) adjacent to the vestibular cerebellum reduce total locus length and locus length per second in the standing position, while anodal stimulation has no effect
The high ICCs for total locus length and locus length per second (>0.9) indicate the strong replicability of these measures (Landis and Koch, 1977). This effect was observed whether the second electrode was on the forehead (Experiment 1) or the right buccinator muscle (Experiment 2), indicating that these decreases depend on the stimulating electrode position near the vestibular cerebellum
Summary
Human balance is controlled by vestibular, visual, and somatosensory inputs to the brainstem and vestibular cerebellum (Peterka and Loughlin, 2004). The cerebellum is involved in motor learning and motor control, and patients with cerebellum dysfunction have a larger sway in the center of gravity while standing (Mauritz et al, 1979; Ilg et al, 2009). Both PET and fMRI show increased cerebellum activity while standing (Ouchi et al, 1999; Jahn et al, 2008), Standing Posture Control consistent with an important function in standing posture control. Reticular formation and lateral vestibular nuclei send projections via the reticulospinal tract and lateral vestibulospinal tract, respectively, to bilateral spinal motor nuclei that contribute to standing posture control. TDCS responses are clearly influenced by polarity (Nitsche and Paulus, 2001; Boros et al, 2008)
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