http://informahealthcare.com/smr ISSN: 0899-0220 (print), 1369-1651 (electronic) Somatosens Mot Res, Early Online: 1–8 ! 2015 Informa UK Ltd. DOI: 10.3109/08990220.2015.1004045 ORIGINAL ARTICLE Effects of aging and tactile stochastic resonance on postural performance and postural control in a sensory conflict task Marius Dettmer 1,2 , Amir Pourmoghaddam 1,2 , Beom-Chan Lee 2 , & Charles S. Layne 2 1 Memorial Bone & Joint Research Foundation, Houston, TX, USA and 2 Center for Neuromotor and Biomechanics Research and Health and Human Performance Department, University of Houston, Houston, TX, USA Abstract Postural control in certain situations depends on functioning of tactile or proprioceptive receptors and their respective dynamic integration. Loss of sensory functioning can lead to increased risk of falls in challenging postural tasks, especially in older adults. Stochastic resonance, a concept describing better function of systems with addition of optimal levels of noise, has shown to be beneficial for balance performance in certain populations and simple postural tasks. In this study, we tested the effects of aging and a tactile stochastic resonance stimulus (TSRS) on balance of adults in a sensory conflict task. Nineteen older (71–84 years of age) and younger participants (22–29 years of age) stood on a force plate for repeated trials of 20 s duration, while foot sole stimulation was either turned on or off, and the visual surrounding was sway-referenced. Balance performance was evaluated by computing an Equilibrium Score (ES) and anterior–posterior sway path length (APPlength). For postural control evaluation, strategy scores and approximate entropy (ApEn) were computed. Repeated-measures ANOVA, Wilcoxon signed-rank tests, and Mann–Whitney U-tests were conducted for statistical analysis. Our results showed that balance performance differed between older and younger adults as indicated by ES (p ¼ 0.01) and APPlength (0.01), and addition of vibration only improved performance in the older group significantly (p ¼ 0.012). Strategy scores differed between both age groups, whereas vibration only affected the older group (p ¼ 0.025). Our results indicate that aging affects specific postural outcomes and that TSRS is beneficial for older adults in a visual sensory conflict task, but more research is needed to investigate the effectiveness in individuals with more severe balance problems, for example, due to neuropathy. Keywords Aging, balance, foot sole vibration, stochastic resonance, tactile receptors History Received 30 September 2014 Revised 18 December 2014 Accepted 23 December 2014 Published online 17 April 2015 Introduction One major concern of the US health care system is improvement of the health of older adults and maintenance of their independence. Falls are the leading cause of traumatic death in older adults (Galica et al. 2009) and therefore the prevention of falls and fall-related injuries in older adults is an important area of research interest. Falls are a factor causing enormous costs for short and longer term patient care and putting a significant burden on the health care system. Each year, non-fatal and fatal falls lead to medical costs of approximately 19 billion and 200 million dollars, respectively (Stevens et al. 2006). Prevention of falls and related injuries is associated with increased quality of life by enabling older adults to remain more independent. Current research efforts are mainly focusing on either improving postural control by employing neuromotor training interventions or by utilizing assistive devices designed to improve complex and potentially impaired sensorimotor control in older adults. It is believed that there are three major portions of postural control: (1) the sensation of position and displacement, (2) processing of afferent signals, and (3) selection and gener- ation of adequate motor responses in order to ensure postural stability or to re-establish postural verticality (Schmidt 1975; Redfern et al. 2001). Due to extended research efforts since the 1990s, today there is a better understanding of modifiable and consistent risk factors associated with falls. For optimal postural control, complex sensorimotor mechanisms and processes are required. If any of the involved systems are perturbed, maintenance of postural control can become challenging. It is well documented that aging negatively influences postural control processes leading to associated declines in balance performance and increases the risk of falls (Amiridis 2003; Shaffer and Harrison 2007; Seidler et al. 2010). More specifically, the vestibular, visual, proprioceptive, and cuta- neous sensory sources become less sensitive to stimuli due to aging. Cutaneous receptors are important contributors of feedback about orientation of the body in space. The uniqueness of the plantar surface and mechanoreceptors of the sole of the foot is that it is a location on the body that directly connects humans to their environment. Plantar Correspondence: M. Dettmer, Memorial Bone & Joint Research Foundation, 1140 Business Center Drive Suite 101, Houston, TX 77043, USA. Tel: +1 713 743 9868. E-mail: marius.dettmer @uth.tmc.edu Somatosens Mot Res Downloaded from informahealthcare.com by 107.202.142.59 on 04/17/15 For personal use only.