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Position and velocity responses to galvanic vestibular stimulation in human subjects during standing
Author(s) -
Wardman Daniel L.,
Day Brian L.,
Fitzpatrick Richard C.
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2003.00293.x
Subject(s) - galvanic vestibular stimulation , vestibular system , stimulation , galvanic cell , position (finance) , audiology , medicine , physical medicine and rehabilitation , psychology , communication , neuroscience , chemistry , organic chemistry , finance , economics
Galvanic vestibular stimulation (GVS) in animals modulates the firing of otolith and semicircular canal afferents alike. Here, we look for postural responses evoked by GVS from the otolith organs and semicircular canals. To minimise the modifying effects of somatosensory input on the response, low‐intensity (0.3–0.5 mA) GVS was applied for 8 s while subjects stood on foam rubber with the feet together and strapped to the floor. The response had three phases: (i) a rapid movement during the first second, (ii) a slower movement that persisted throughout the stimulus, and (iii) a rapid partial return movement after GVS stopped. The three movement velocities were significantly different. The GVS response therefore appears to be the sum of a step response that returns to the starting point when the stimulus stops, and a constant‐velocity ramp response for the duration of the stimulus without a return movement. Subjects' responses differed in size and profile, some with the step or ramp responses almost exclusively but most with a combination of both. The ‘step‐plus‐ramp’ model was tested by comparing the three velocities. If the responses add, the initial velocity should not be different from the sum of the velocities during the ramp‐only period and the step‐only period at offset. ANOVA and pairwise comparisons confirmed this. It is concluded that postural responses to GVS arise through stimulation of both otolith and canal afferents.