Processing moving visual scenes during upright stance in elderly patients with mild cognitive impairment.

BACKGROUND: The ability to maintain balance in an upright stance gradually worsens with age and is even more difficult for patients with cognitive disorders. Cognitive impairment plays a probable role in the worsening of stability. The purpose of this study was to expose subjects with mild cognitive impairment (MCI) and healthy, age-matched controls to moving visual scenes in order to examine their postural adaptation abilities. METHODS: We observed postural responses to moving visual stimulation while subjects stood on a force platform. The visual disturbance was created by interposing a moving picture in four directions (forward, backward, right, and left). The pre-stimulus (a static scene for 10 s), stimulus (a dynamic visual scene for 20 seconds) and post-stimulus (a static scene for 20 seconds) periods were evaluated. We separately analyzed the total path (TP) of the center of pressure (COP) and the root mean square (RMS) of the COP displacement in all four directions. RESULTS: We found differences in the TP of the COP during the post-stimulus period for all stimulus directions except in motion towards the subject (left p = 0.006, right p = 0.004, and away from the subject p = 0.009). Significant RMS differences between groups were also observed during the post-stimulus period in all directions except when directed towards the subject (left p = 0.002, right p = 0.007, and away from the subject p = 0.014). CONCLUSION: Exposing subjects to a moving visual scene induced greater destabilization in MCI subjects compared to healthy elderly controls. Surprisingly, the moving visual scene also induced significant aftereffects in the MCI group. Our findings indicate that the MCI group had diminished adaptation to the dynamic visual scene and recovery. These results suggest that even mild cognitive deficits can impair sensory information integration and alter the sensory re-weighing process.

Assessment of Visual Reliance in Balance Control: An Inexpensive Extension of the Static Posturography.

Ability of humans to maintain balance in an upright stance and during movement activities is one of the most natural skills affecting everyday life. This ability progressively deteriorates with increasing age, and balance impairment, often aggravated by age-related diseases, can result in falls that adversely impact the quality of life. Falls represent serious problems of health concern associated with aging. Many investigators, involved in different science disciplines such as medicine, engineering, psychology, and sport, have been attracted by a research of the human upright stance. In a clinical practice, stabilometry based on the force plate is the most widely available procedure used to evaluate the balance. In this paper, we have proposed a low-cost extension of the conventional stabilometry by the multimedia technology that allows identifying potentially disturbing effects of visual sensory information. Due to the proposed extension, a stabilometric assessment in terms of line integral of center of pressure (COP) during moving scene stimuli shows higher discrimination power between young healthy and elderly subjects with supposed stronger visual reliance.

A sensitivity comparison of clinical tests for postural instability in patients with Huntington's disease.

Falls are a common complication in Huntington's disease (HD) and detection of postural instability (PI) may be useful for identifying patients who are at risk of falls. The aim of our study was to find the most sensitive clinical test for PI in patients with HD and to correlate PI with the other symptoms. 20 HD patients were examined using: (1) The Unified Huntington's Disease Rating Scale (UHDRS), (2) The Mini Mental State Examination (MMSE) and (3) six clinical tests for PI. Inter-scale and test correlations were inspected and uni-dimensionality, validity, and measurement precision were analyzed using a factor analysis model/latent PI score. PI was compared with information obtained from surveys completed independently by patients and caregivers, and both reports were evaluated for absolute agreement using intraclass correlations (ICCs). PI was found in 16 patients; the tests correlated better with caregivers' reports (r=0.78) than patients' responses. The validity of the patients' answers decreased with the level of MMSE scores. PI correlated with MMSE (r=0.64, p<0.01), the subscale score for voluntary movements (r=0.86, p<0.01), the overall motor subscore (r=0.73, p<0.01), and the Luria test subscore (r=0.87, p<0.01). The stance with feet close together and tandem gait correlated best with the latent PI score, and factor loadings confirmed they were the most sensitive tests for PI detection in HD.