Study of the postural muscles control in subjects with different retinal functionality

Aim: The self-motion perception produced by optic flow fields is part of the sensorimotor integration process finalized to the postural control. Depending on the stimulated portion of the retina, the corticocortical signals are differently processed. The aim was to investigate if retinal impairments modify the activity of postural muscles. Methods: We evaluated the electromyographic (EMG) activity of the tibialis anterior and soleus in 34 volunteers. Thirteen people at early stage of retinopathy were included in the ‘‘retinopathy group’’ (average age 62), eight people with a laser treatment on the peripheral retina were included in the ‘‘laser group’’ (average age 62) and thirteen healthy subjects formed the ‘‘control group’’ (average age 59). The EMG activity was recorded while the subjects viewed radial optic flow stimuli presented in the foveal, peripheral and full visual field. A repeated measures ANOVA was performed on the normalized EMG of each muscle, with side (right–left) as within-factor and group and stimuli as between-factors. Results: The EMG analysis of the tibialis showed a significant effect for group (p = 0.012) and an interaction effect side by group (p = 0.06). The EMG analysis of the soleus showed a significant effect for group (p\0.001) and an interaction effect side by group (p\0.001). Further, the retinopathy group showed the highest values of muscles activation, while the laser group presented the lowest. The retinopathy and the laser groups activated predominantly muscles of the same side, left and right respectively. The control group activated left tibialis and right soleus. Conclusion: Results showed that the retinal functionality influences the activity of postural leg muscles. We hypothesize that in presence of retinal damage the postural control system may induce a co-contraction of leg muscles in order to maintain stability. Results seem to indicate that an impairment of the peripheral retina reduces the muscles activity. References 1. Peterka, R. J. (2002). Sensorimotor integration in human postural control. Journal of neurophysiology, 88(3), 1097–1118 2. Raffi, M., Piras, A., Persiani, M., & Squatrito, S. (2014). Importance of optic flow for postural stability of male and female young adults. European journal of applied physiology, 114(1), 71–83. 3. Raffi, M., & Siegel, R. M. (2004). Multiple cortical representations of optic flow processing. In Optic flow and beyond (pp. 3–22). Springer Netherlands.