Older adults rely on somatosensory information from the effector limb in the planning of discrete movements to somatosensory cues

Age-related effects on dynamic postural stability and prefrontal cortex activation during precision fitting tasks

Background

Dynamic postural control is impaired in older adults, as evidenced from worse dynamic postural stability compared to young adults during upright stance while concurrent goal-directed tasks. Prefrontal cortex (PFC) is considered to play an important role in goal-directed tasks. This study aimed to investigate the age effects on dynamic postural stability and PFC activation during precision fitting tasks.

Methods

Participant performed precision fitting tasks under four different conditions: large opening size with their arm's length (close-large), small opening size with their arm's length (close-small), large opening size with 1.3 times arm's length (far-large), and small opening size with 1.3 times arm's length (far-small). We analyzed the center of pressure-related outcomes representing dynamic postural stability and PFC activation at the six different subregions from healthy older adults (n = 15, 68.0 ± 3.5 years), and gender-matched middle-aged (n = 15, 48.73 ± 3.06 years) and young (n = 15, 19.47 ± 0.64 years) adults.

Results

The dynamic postural stability presented the young > middle-aged > older groups across the conditions. Specifically, the young group presented better dynamic postural stability than the older group in the close-large, far-large, and far-small conditions (p < .05), while showed better dynamic postural stability than the middle-aged group in the close-large condition (p < .05). Additionally, the older group had greater PFC activation at all PFC subregions than the young group (p < .05), while had greater activation at left dorsolateral and ventrolateral PFC than the middle-aged group (p < .05). The middle-aged group presented greater activation at left dorsomedial PFC than the young group (p < .05).

Conclusion

Heightened dorsomedial PFC activation in middle-aged adults compared to young adults may reflect a deficit in processing the visuomotor information during the precision fitting tasks. Degeneration of the ability in automatic coordination of dynamic postural control may begin to occur at midlife.

Does visual experience influence arm proprioception and its lateralization? Evidence from passive matching performance in congenitally-blind and sighted adults

In humans, body segments' position and movement can be estimated from multiple senses such as vision and proprioception. It has been suggested that vision and proprioception can influence each other and that upper-limb proprioception is asymmetrical, with proprioception of the non-dominant arm being more accurate and/or precise than proprioception of the dominant arm. However, the mechanisms underlying the lateralization of proprioceptive perception are not yet understood. Here we tested the hypothesis that early visual experience influences the lateralization of arm proprioceptive perception by comparing 8 congenitally-blind and 8 matched, sighted right-handed adults. Their proprioceptive perception was assessed at the elbow and wrist joints of both arms using an ipsilateral passive matching task. Results support and extend the view that proprioceptive precision is better at the non-dominant arm for blindfolded sighted individuals. While this finding was rather systematic across sighted individuals, proprioceptive precision of congenitally-blind individuals was not lateralized as systematically, suggesting that lack of visual experience during ontogenesis influences the lateralization of arm proprioception.

A review of center of pressure (COP) variables to quantify standing balance in elderly people: Algorithms and open-access code

Postural control is often quantified by recording the trajectory of the center of pressure (COP)-also called stabilogram-during human quiet standing. This quantification has many important applications, such as the early detection of balance degradation to prevent falls, a crucial task whose relevance increases with the aging of the population. Due to the complexity of the quantification process, the analyses of sway patterns have been performed empirically using a number of variables, such as ellipse confidence area or mean velocity. This study reviews and compares a wide range of state-of-the-art variables that are used to assess the risk of fall in elderly from a stabilogram. When appropriate, we discuss the hypothesis and mathematical assumptions that underlie these variables, and we propose a reproducible method to compute each of them. Additionally, we provide a statistical description of their behavior on two datasets recorded in two elderly populations and with different protocols, to hint at typical values of these variables. First, the balance of 133 elderly individuals, including 32 fallers, was measured on a relatively inexpensive, portable force platform (Wii Balance Board, Nintendo) with a 25-s open-eyes protocol. Second, the recordings of 76 elderly individuals, from an open access database commonly used to test static balance analyses, were used to compute the values of the variables on 60-s eyes-open recordings with a research laboratory standard force platform.