Postural sway reduction in aging men and women: relation to brain structure, cognitive status, and stabilizing factors

Abstract

Postural stability becomes compromised with advancing age, but the neural mechanisms contributing to instability have not been fully explicated. Accordingly, this quantitative physiological and MRI study of sex differences across the adult age range examined the association between components of postural control and the integrity of brain structure and function under different conditions of sensory input and stance stabilization manipulation. The groups comprised 28 healthy men (age 30-73 years) and 38 healthy women (age 34-74 years), who completed balance platform testing, cognitive assessment, and structural MRI. The results supported the hypothesis that excessive postural sway would be greater in older than younger healthy individuals when standing without sensory or stance aids, and that introduction of such aids would reduce sway in both principal directions (anterior-posterior and medial-lateral) and in both the open-loop and closed-loop components of postural control even in older individuals. Sway reduction with stance stabilization, that is, standing with feet apart, was greater in men than women, probably because older men were less stable than women when standing with their feet together. Greater sway was related to evidence for greater brain structural involutional changes, indexed as ventricular and sulcal enlargement and white matter hyperintensity burden. In women, poorer cognitive test performance related to less sway reduction with the use of sensory aids. Thus, aging men and women were shown to have diminished postural control, associated with cognitive and brain structural involution, in unstable stance conditions and with diminished sensory input.

Fig. 1

Examples of sway paths (anterior–posterior and medial–lateral directional average) for one trial performed by a 31-year-old man (top) and a 66-year-old man (bottom). The left panel of sway paths displays performance without any experimental aid, and the right panel shows performance when provided all three experimental aids. Note the exaggerated sway path in the no-aid condition of the older man.

Fig. 2

Examples of brain regions measured. (a) Ventricular system of a 66-year-old man: yellow tones = frontal ventricles; pink tones = body of the ventricles; green tones = occipital ventricles; turquoise = third ventricle. (b) Supratentorial CSF: sagittal, coronal, and axial views of a late-echo fast spin echo image of a 70-year-old man with CSF as the bright intensity and the supratentorial volume outlined in turquoise. (c) White matter hyperintensities: FLAIR images of a 69-year-old woman with WMHI evident in the periventricular zone. (d) Anterior superior vermis: early echo and late echo of a fast spin echo study of a 72-year-old woman with the vermian region of interest noted by the yellow arrow.

Fig. 3

Means ± S.E. sway path lengths for the feet-together and feet-apart conditions with eyes open vs. closed and with and without touch for men and women. Note that the data from the men represent a subset published in Sullivan et al. (2006).

Fig. 4

Means ± S.E. directional sway path for the feet-together and feet-apart conditions with eyes open vs. closed and with and without touch for men and women. Note that the data from the men represent a subset published in Sullivan et al. (2006).

Fig. 5

Correlations between each sway path length and age for the men and the women. Note the correlation coefficients in the legend.

Fig. 6

Correlations of the sway-reduction index with age in the men and the women. Note the correlation coefficients in the legend.

Fig. 7

Greater supratentorial CSF volume correlated with longer sway path lengths in the men.

Fig. 8

Greater white matter hyperintensity burden (WMHI) correlated with longer sway path lengths in the women.

Fig. 9

Lower Dementia Rating Scale scores correlated with longer sway path lengths in the women.

Fig. 10

The grand average of the average squared displacement of pairs of points over time of the 12 younger men (<50 years old) and 16 older men (>50 years old). The top pair of curves displays the grand averages of the younger (gray lines) and older (black lines) for the eyes closed/no touch/feet-together condition; the bottom pair displays the grand averages of each group, which appear overlapping, for the eyes open/touch/feet-apart condition. The fast rising arm of the curves reflects the short-term, open-loop component of the sway diffusion, and the flatter sloped curve reflects the long-term, closed-loop component. The critical point is the intersection between the short-term and long-term slopes.