Crosstalk opposing view: Fear of falling does not influence vestibular-evoked balance responses.

摘要: Fear of falling becomes more common as we age and increases following a fall (Murphy & Isaacs, 1982). itself may also increase the likelihood future falls. Delbaere et al. (2010) found that risk is determined not only by physiological predictors (e.g. weakness, poor vision) past history, but independently perceived itself. This raises possibility perception coupled with motivation to prevent can induce deleterious changes in sensorimotor control balance (Young Mark, 2015). Understanding these important if are reveal mechanisms leading fall. A recent paper The Journal Physiology Horslen (2014) suggested fear postural responsiveness vestibular input this underlie altered fearful state. However, our own research suggests response stimulation largely unaffected (Osler 2013). Here discuss apparent discrepancy. Horslen described influence threat upon responses when healthy adults stood on edge platform elevated 3.2m. continuous stochastically varying current was applied ears modulate nerve activity (2–25Hz; 1.1mA root mean square), ongoing recorded using force platform. stimulus–response relationship quantified cross-correlation cross-spectral analysis. At height, magnitude increased compared ground. Frequency analysis revealed an gain, mainly at high frequencies (>5 Hz). authors concluded processing information behaviour height. Osler (2013) adopted similar approach, exposing height 3.85m while standing plank 22cm wide. Instead stochastic stimulus (SVS), however, ‘galvanic’ applied, consisting square-wave (2s; 1mA). In circumstances, early component stimulus-evoked body sway (<800 ms) indistinguishable between Beyond time, caused large reduction response. extent correlated skin conductance, measure sympathetic arousal fear. Our interpretation feedforward coupling motor fear, reflected unchanged component. Only sensory feedback became available from other sources proprioception) suppressed, smaller late Thus, undoubtedly affected do attribute per se. Why discrepancy two papers? We believe it due differences characteristics outcome measures, well differing interpretations. Relevance balance The SVS used deliberately engineered produce minimal sway. Application time-varying oscillates around zero removing below 2Hz precludes development any significant (Dakin 2010). were observed ground reaction forces, does challenge evoking sustained direction. Furthermore, reported high-frequency Whatever effects demonstrated, their relevance uncertain. To investigate balance, use challenges system. therefore 2 s constant-current stimulus, which evoked towards narrow plank, thus directly challenging balance. contained substantial power low within bandwidth human movement. be sure they relevant balance. Outcome measures The combined spectral analysis, maximizes statistical sensitivity for detecting small gain response, case (2014). given multisegmental nature body, forces alone identify location vestibular-evoked muscle generation. uncertain kinematic location, frequency range (strongest effect above 5 Hz), makes whether have consequence balance. For primary importance centre mass relation base support. To assess control, measured movement direction ‘dangerous’ edge. key result during phase, prior integration proprioceptive information, position velocity agree methods less sensitive identifying early, With sufficient participants, conditions statistically detectable. point such difference centre-of-mass even smaller. While little change identified considerable suppression Therefore, there extremely subtle and, crucially, dispute veracity results presented (2014), question relevance. Interpretation results What implications balance? answer requires comparative effect, attributed processing, later involving all modalities. In (2013), conductance confirmed subjects physiologically Despite this, despite no galvanic stimulation. conclude best unproven Does has Quite contrary! minimized stage, non-vestibular time exert effectively arresting stimulus. It likely affects multisensory posture. Given strength fall, unsurprising some processes. More surprising unaltered. contend confused significance functional significance. Compared falling, accurate impervious appears functionally manner.