Analyses of the cortical hemodynamic responses related to postural control during sensory conflict using near-infrared spectroscopy (NIRS) - Application in vestibular rehabilitation

Abstract

Coherent integration of multisensory inputs, especially visual, vestibular and somatosen-sory cues, is essential for appropriate self-motion perception, and sensory mismatch (i.e., sensory conflict) among different sensory information during body motion induces vertigo and instability of posture. To elucidate the cortical roles in the maintenance of postural stability under sensory conflict situations, we recorded the cortical hemodynamic activity using near-infrared spectroscopy (NIRS) while the subjects underwent the sensory organization test (SOT) protocol that systematically disrupts sensory integration processes. In healthy subjects, we found activation in the temporoparietal junction (TPJ), the posterior parietal cortex (PPC), the premotor cortex (PMC), and the supplementary motor area (SMA) under various conditions. The activation patterns of these cortical areas in response to specific combinations of SOTs suggested that 1) the TPJ might be involved in the process of sensory reweighting; 2) the SMA and PMC might be essential for the voluntary cortical motor control in sensory conflict; 3) activation of the PPC might be involved in the updating and computation of spatial orientation in sensory conflict. In two patients with chronic vertigo induced by unilateral vestibular neuritis, the PPC, SMA and PMC were activated under SOT 3 or 4 and the SOT condition that activated these regions the most differed among subjects, suggesting that the dependent sensory input (i.e., visual or somatosensory input) to maintain the standing balance in sensory conflict situations might differ among patients with chronic vertigo. In recent studies, the neurofeedback therapy using fNIRS has received attention as a novel rehabilitation technique for post-stroke or psychiatric patients. We propose that the neurofeedback therapy using fNIRS will become a promising therapeutic tool for patients with intractable chronic vertigo.