I still have a problem with proprioception and I'm sure that unless I find a solution nobody else will.
http://journal.frontiersin.org/article/10.3389/fnagi.2015.00097/full?utm_source=newsletter&
Isabella Katharina Wiesmeier,
Daniela Dalin- Klinik für Neurologie und Neurophysiologie, Universität Freiburg, Freiburg, Germany
Introduction
Postural control in elderly people is impaired by numerous factors [for an overview, see, e.g., Shumway-Cook and Woollacott (2001) and Iosa et al. (2014)]. Changes in sensory systems include a reduced joint position sense at the ankle (Horak et al., 1989; Goble et al., 2009), paralleled by a higher perception threshold for vibration (Tang and Woollacott, 1996; Hilz et al., 1998; Lin et al., 2005; Shaffer and Harrison, 2007).
Moreover, visual function (visual acuity, contour and depth perception,
contrast sensitivity, peripheral vision) is reduced, partly due to
structural changes of the eye. In addition, a decrease of vestibular
function has been described (Bergström, 1973; Rosenhall, 1973; Merchant et al., 2000; Park et al., 2001; Rauch et al., 2001; Shumway-Cook and Woollacott, 2001; Nag and Wadhwa, 2012; Grossniklaus et al., 2013).
Impairments of the motor system in the elderly have numerously been reported [e.g., Doherty (2003), Macaluso and De Vito (2004), and Reeves et al. (2006)]. For example, a 40% reduction of the lower body muscle strength was found when compared to young healthy adults (Shumway-Cook and Woollacott, 2001). During balance corrections, elderly people display an altered muscle response organization (Shumway-Cook and Woollacott, 2001; Tsai et al., 2014) and more frequent coactivations of antagonist muscles (Shumway-Cook and Woollacott, 2001; Macaluso and De Vito, 2004; Klass et al., 2007; Papegaaij et al., 2014).
Some authors proposed deficits in higher-level adaptive systems [e.g., Shumway-Cook and Woollacott (2001)]. They suggested that elderly people’s ability to adapt to external perturbations is diminished (Horak et al., 1989; Peterka and Black, 1990; Mansfield and Maki, 2009). Elderly people react with longer onset latencies to external perturbations than young adults do (Woollacott et al., 1988; Horak et al., 1989; Woollacott and Shumway-Cook, 1990; Tsai et al., 2014). In addition, elderly people seem to have difficulties in sensory reweighting (Horak et al., 1989; Teasdale and Simoneau, 2001; Eikema et al., 2012, 2014). The term “sensory reweighting” was established by Nashner et al. (1982)
to describe a process of scaling the relative importance of sensory
cues (visual, vestibular, and proprioceptive) for motor control (Nashner et al., 1982; Jeka et al., 2006). However, the sensory weighting process itself seems to be unimpaired in elderly people (Allison et al., 2006; Jeka et al., 2006), indicating that differences in sensory weights between elderly and young people are related to different sensory preferences.
Measures of human postural control are usually
segregated into spontaneous sway measures and measures of motor behavior
induced by external perturbations. Age-related differences in
spontaneous sway mainly concern increases in mean velocity (MV) and mean
frequency (MF) (Maki et al., 1990; Hytönen et al., 1993; Baloh et al., 1994; Collins et al., 1995; Prieto et al., 1996; Maurer and Peterka, 2005; Qu et al., 2009).
During perturbed stance, somatosensory cues affect postural control in young people differently than in elderly people [e.g., Peterka and Black (1990), Speers et al. (2002), Fransson et al. (2004), Ghulyan et al. (2005), and Maitre et al. (2013)].
In general, stance of elderly people is reported to be less stable with
absent or altered proprioceptive, vestibular, and visual information (Peterka and Black, 1990; Whipple et al., 1993; Speers et al., 2002; Rosengren et al., 2007; Liaw et al., 2009; Pierchała et al., 2012; Maitre et al., 2013; Eikema et al., 2014),
leading to larger body excursions. Some authors evaluated the
relationship between the perturbation and the induced body motion in
terms of transfer functions [see Materials and Methods, see also Nashner and McCollum (1985), Ishida et al. (1997), Van der Kooij et al. (2001), Peterka (2002), Maurer and Peterka (2005), Masani et al. (2006), Maurer et al. (2006a), Vette et al. (2010), Davidson et al. (2011), Nishihori et al. (2012), and Van der Kooij and Peterka (2011)].
Transfer functions are frequently interpreted using a model-based
approach. These models usually involve inverted pendulum bodies, a
neural controller including a proportional (stiffness of the system) and
a derivative feedback gain (damping of the system), and a feedback time
delay. The proportional gain is proportional to the sensory error
signal and the derivative gain is proportional to the time derivative of
the sensory error signal. Both factors are added up as a motor output
to provide corrective ankle torque, thereby stabilizing the inverted
pendulum and reducing oscillations (Peterka, 2002; Vette et al., 2010). The feedback time delay represents the lumped time delays of sensory, central, and motor transduction (Peterka, 2002).
The sensory weighting mechanism of the model scales the gains of the
sensory cues (proprioceptive, vestibular, and visual) in terms of
relative contributions to the overall feedback gain (Maurer et al., 2006a; Van der Kooij and Peterka, 2011; Engelhart et al., 2014).
Recently, some authors applied the model-based approach to postural control data of elderly people (Cenciarini et al., 2009, 2010; Davidson et al., 2011; Nishihori et al., 2012; Maurer and Peterka, 2005). During quiet stance, elderly people seem to have an increased proportional gain of the sensorimotor control system (Maurer and Peterka, 2005; Nishihori et al., 2012). During external perturbations, an increased derivative gain of the system has been reported (Cenciarini et al., 2009, 2010; Davidson et al., 2011), whereas reports of the system’s proportional gain were controversial (Cenciarini et al., 2009, 2010; Davidson et al., 2011), depending, for example, on the direction of sway.
In the current study, we aimed to find out whether we
are able to detect sensory, motor, and higher-level adaptation deficits
mentioned above in postural control behavior of the elderly. In
addition, we aimed to identify which of these contributors most
significantly influence postural control in the elderly. For that, we
assessed both, spontaneous sway parameters and applied external
perturbations in young, middle-aged, and elderly people. The subjects’
reactions to anterior–posterior platform tilts were analyzed at 11
frequencies with eyes closed or open, using different amplitudes, with
the purpose to simultaneously identify the major components of the
sensorimotor control system and their modifications as a function of
age. We hypothesized that degradations of sensory, motor, and
higher-level adaptation deficits in elderly could be extracted from
postural control behavior. As our model-based approach is highly
sensitive to changes in the sensory-motor system, it might be valuable
in future for differentiating between age-related and pathology-related
impairments of postural control, and for evaluating therapeutic
interventions that ameliorate postural control in elderly.
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