Presenter: Jonathan Wallace
Faculty Mentor: Brain Dalton, Marjorie Woollacott
Presentation Type: Oral
Primary Research Area: Science
Major: Human Physiology
Maintaining standing balance involves processing of vestibular, visual, and somatosensory information to produce dynamic motor responses. The purpose of this experiment was to determine if intrinsic foot muscles are modulated by vestibular activity and if the medium-latency responses are altered by changes in head position and visual cues. Indwelling electromyography (EMG) of the abductor hallucis (AH) and abductor digiti minimi (ADM) were sampled while bilateral electrical vestibular stimulation (EVS) was administered to quietly standing participants. Vestibular stimulation delivered on the mastoid processes is interpreted as a true head acceleration which creates a medium- latency vestibular-evoked balance response. A cumulant density function (i.e. cross-correlation) was used to analyze EVS input and the muscle activity (output). When the head was positioned 90◦ to the left with the eyes closed, the medium-latency response amplitude was -0.122 ± 0.027 in the AH and 0.130 ± 0.048 in the ADM. Visual cues reduced the medium-latency amplitude by 14 and 23% in the AH and ADM, respectively (p < 0.05). When the head was oriented 90◦ to the right, the medium-latency response was opposite for the AH (0.101 ± 0.042) and ADM (0.065 ± 0.026, p < 0.05). The inversion and reduction of the medium-latency response with changes to head position and visual input indicate that the vestibular system is modulating activity in the ADM and AH. These results may suggest that the ADM and AH muscles are important contributors to standing balance control.