Monaural and binaural galvanic vestibular stimulation in human dynamic balance function

Spontaneous dynamic balance reactions to galvanic binaural and monaural stimulation were investigated in lateral sway. Low-intensity currents were used to stimulate the vestibular apparatus of subjects, who were standing with their eyes closed on a rocking platform. Head and body base movements were measured in the lateral plane, simultaneously. In monaural as well as in binaural stimulation mode, the onset of the current induced a lateral biphasic stereotyped postural responses: firstly the pressure centre moved towards the cathode side then the whole body swayed towards the anode side. The cut-off of the current resulted in a similar pattern of movement but in the opposite direction. Two main features characterised the response obtained in monaural mode. First, the amplitude of the dynamic balance response was half the size of that recorded in binaural stimulation mode. Second, cathodal monaural stimulation on one side or anodal monaural stimulation on the opposite side elicited superimposable responses. The results demonstrate that in healthy subjects, postural response to binaural galvanic vestibular stimulation results from the linear sum of two equivalent stimulations: one from the cathodal excitation and the other from the anodal inhibition. The method could be used in clinical studies to detect vestibular asymmetries and dysfunction.