Effects of stochastic vestibular stimulation on cognitive performance in children with ADHD.

Previous work has shown that exposure to auditory white noise (WN) can improve cognitive performance in children with ADHD, but it is unknown whether this improvement generalizes to other sensory modalities. To address this knowledge gap, we tested the effect of Stochastic Vestibular Stimulation (SVS) on cognitive performance and reaction time (RT) variability in two groups: children with ADHD and typically developing children (TDC). Children with ADHD (N=42) and TDC (N=28) performed three cognitive tasks (Spanboard, Word Recall and N-back tasks) at two different occasions, with and without exposure to SVS, in a double blinded design. The results showed no main effects of SVS on neither performance nor RT variability for children in any of the groups, and no interactions between SVS and group. Based on these results we conclude that, using our stimulation protocol, the positive effects of WN exposure on cognition in children with ADHD do not generalize to Stochastic Vestibular Stimulation.

The direction of the postural response to a vestibular perturbation is mediated by the cerebellar vermis.

When an electrical stimulus is applied to perturb the vestibular system, a postural response is generated orthogonal to head orientation. It has previously been shown that there is a convergence of neck proprioceptive and vestibular input within the cerebellum to provide a head-on-body reference frame (Manzoni et al. in Neuroscience 93:1095-1107, 1999). The objective of this experiment was to determine whether the direction of the postural response to a vestibular perturbation is modulated when function of the cerebellar vermis is temporarily depressed. Twenty participants were randomly assigned to a SHAM group (paired-pulse transcranial magnetic stimulation) or a TEST group (continuous theta burst stimulation). Stochastic vestibular stimulation (SVS) was applied to standing subjects with their head facing forward or over their left shoulder. Cumulant density traces were established between the SVS and shear force over 180°, and the peak amplitude determined the direction of sway. There were no significant changes in sway direction when the head was facing forward for either stimulation (TEST or SHAM; p = 0.889) or when the head was facing over the shoulder for the SHAM condition (p = 0.954). There was, however, a significant change in sway direction when the head was turned with a depressed cerebellum (p = 0.018); from the expected antero-posterior direction, orthogonal to head orientation, to one slightly more mediolateral with respect to the feet. These results suggest the cerebellum plays a role in the integration of input to generate an appropriately directed postural response relative to the head position.