Foot Somatosensory Information Contributes To Quiet Stance

Hassanpour, Seyedehmaryam
Most of the posture and balance studies have mentioned that in human beings, balance is achieved and maintained by a complex set of control systems that include sensory input from vision (sight), proprioceptive sensors of the muscles, somatosensory senses from skin receptors (touch), and the vestibular system (motion, equilibrium, spatial orientation). Based on previous studies, postural movement strategies are known to be highly affected by both somatosensory and vestibular information [23]. The present study therefore examines the roles of somatosensory information in the coordination of postural control during quiet stance in different vision and surface conditions. The role of somatosensory information was examined by comparing postural responses of healthy subjects prior to (S+) and following somatosensory loss (S-) due to the anesthetic injected around the peripheral sensory nerve (N. Tibialis). Three force and three-moment signals along and about x-y-z-axes, respectively were acquired at a sampling rate of 100 Hz by a force-plate (Bertec , FP1212-25 custom made 1200×1200mm). Center-of-pressure (CoP) signals at antero-posterior (AP, CoPx) and medio-lateral (ML, CoPy) directions were then computed. 90-seconds long quiet stance data was collected from 10 healthy right handed male subjects at Eyes open and Eyes closed positions, rigid and compliant surface and sense prior to (S+) and following somatosensory loss (S-) conditions. The data were analyzed in both time and frequency domains. In time domain, pathlength and variance of displacement and velocity of postural sway were computed through CoP signals for each subject. In frequency domain, Fast Fourier Transformation (FFT), Power Spectral Density (PSD) Function Estimates, area under the first spectral peak of PSD estimates, centroidal Frequency and frequency dispersion through PSD estimates were computed. We have found that subjects traverse a larger distance in eyes close trials at S+ and compliant surface at S- condition. The subjects have shown a larger variability in CoPx direction compared to CoPy before and after injection. On the other hand, variability observed at rigid surface decreased while variability at compliant surface increased by creating the somatosensory loss, where behavior of the subjects was significantly different at two surfaces at both conditions (S+ versus S-). Furthermore, variance during postural sway was significantly higher at eye closed condition at S- only. The area under the first spectral peak of CoPx is found to be larger than CoPy, where postural sway along x-axis is known to be much unstable than along y-axis. Centroidal frequency (CFREQ) of CoPy has been shown to be significantly higher than CFREQ of CoPx. We have concluded that somatosensory originated information (active touch) is important to recognize the contact surface in control of human posture. In addition, postural behavior triggered by different senses, which do have ecological meanings such as vestibular-visual versus vestibular-somatosensory originated spatial search has been observed to be working in different frequency bands. 
Citation Formats
S. Hassanpour, “Foot Somatosensory Information Contributes To Quiet Stance,” M.S. - Master of Science, Middle East Technical University, 2016.