Physical resilience in older adults: Potential use in promoting healthy aging

Physical resilience is a dynamic concept referring to the physiological response when the body is exposed to stressors. The level of physical resilience is the sum of underlying physiological reserves. Moreover, it may not only be determined by age, genetics, or exposure to a variety of diseases, but is also closely related to the psychological, social, and environmental factors of an individual. This paper summarizes our present understanding of the relationship between physical resilience and other concepts closely related to it. Furthermore, we illustrate the current research progress on physical resilience models and clinical resilience assessment. Besides, this paper intends to present a better understanding of physical resilience and its use in treatment decision-making, personalized diagnosis and disease management, and prevention and rehabilitation strategies.     

Evidence for motor cortex dedifferentiation in older adults

Older adults (OA) show more diffuse brain activity than young adults (YA) during the performance of cognitive, motor, and perceptual tasks. It is unclear whether this overactivation reflects compensation or dedifferentiation. Typically, these investigations have not evaluated the organization of the resting brain, which can help to determine whether more diffuse representations reflect physiological or task-dependent effects. In the present study we used transcranial magnetic stimulation (TMS) to determine whether there are differences in motor cortex organization of both brain hemispheres in young and older adults. We measured resting motor threshold, motor evoked potential (MEP) latency and amplitude, and extent of first dorsal interosseous representations, in addition to a computerized measure of reaction time. There was no significant age difference in motor threshold, but we did find that OA had larger contralateral MEP amplitudes and a longer contralateral MEP latency. Furthermore, the spatial extent of motor representations in OA was larger. We found that larger dominant hemisphere motor representations in OA were associated with higher reaction times, suggesting dedifferentiation rather than compensation effects.     

Segmental control for adaptive locomotor adjustments during obstacle clearance in healthy young adults

Anticipatory locomotor adjustments (ALAs) are used during locomotion to perform tasks, such as obstacle clearance, although not much is known as to how these ALAs are implemented by the central nervous system (CNS). The current study applied the planar law of intersegmental coordination to both leading and trailing limbs in a paradigm in which obstacle height and depth were manipulated to propose how ALAs are controlled. Ten healthy young adults stepped over nine obstacle conditions. Full-body 3D kinematic data were collected and elevation angles of the foot, shank, and thigh in the sagittal plane were calculated. For each limb within each trial, a principal component analysis was applied to limb segment trajectories. As well, a Fourier harmonic series was used to represent segment elevation angle trajectories, and phase differences between adjacent segments were determined. Planarity was consistently high in both limbs for all obstacle conditions, although significant differences between obstacle heights were observed. Increases in covariance loop width and rotation of the covariance plane accompanied changes in planarity. As observed in previous studies, fundamental harmonic phase differences between adjacent segments were highly correlated to plane characteristics and these phase differences changed systematically with increases in obstacle height. From the results, it is proposed that if a given environment requires a change in locomotion, the CNS adjusts a basic locomotor pattern if needed through the manipulation of the phase differences in the fundamental harmonics of the elevation angles between adjacent segments and elevation angle amplitude (with a constraint being intersegmenal elevation angle planarity).     

Structure of four executive functioning tests in healthy older adults

The authors examined the factor structure of 4 indicators of executive functioning derived from 2 new (i.e., Hayling and Brixton) and 2 traditional (i.e., Stroop and Color Trails) tests. Data were from a cross-sectional sample of 55- to 85-year-old healthy adults (N=427) from the Victoria Longitudinal Study. Confirmatory factor analysis (LISREL 8.52) tested both a 2-factor model of Inhibition (Hayling, Stroop) and Shifting (Brixton, Color Trails) and a single-factor model. The 2-factor model did not fit the data because the covariance matrix of the factors was not positive definite. The single-factor model fit the data well, chi(2)(2, N=427)=0.32, p=.85, root-mean-square error of approximation (RMSEA)=.00, comparative fit index (CFI)=1.00, goodness-of-fit index (GFI)=1.00. Moreover, the single-factor structure of executive functioning was invariant (configural and metric) across gender, and invariant (configural with limited metric) across age. Structural relations showed that poorer executive functioning performance was related to older age and lower fluid intelligence, chi(2)(11, N=418)=23.04, p=.02, RMSEA=.05, CFI=.97, GFI=.98.     

Vitamin K status and cognitive function in healthy older adults

Evidence is accumulating that vitamin K could have a role in cognition, especially in aging. Using data from the Québec Longitudinal Study on Nutrition and Successful Aging (NuAge), a cross-sectional analysis was conducted to examine the associations between vitamin K status, measured as serum phylloquinone concentrations, and performance in verbal and non-verbal episodic memory, executive functions, and speed of processing. The sample included 320 men and women aged 70 to 85 years who were free of cognitive impairment. After adjustment for covariates, higher serum phylloquinone concentration (log-transformed) was associated with better verbal episodic memory performances (F = 2.43, p = 0.048); specifically with the scores (Z-transformed) on the second (β = 0.47; 95% confidence interval [CI] = 0.13–0.82), third (β = 0.41; 95% CI = 0.06–0.75), and 20-minute delayed (β = 0.47; 95% CI = 0.12–0.82) free recall trials of the RL/RI-16 Free and Cued Recall Task. No associations were found with non-verbal episodic memory, executive functions, and speed of processing. Our study adds evidence to the possible role of vitamin K in cognition during aging, specifically in the consolidation of the memory trace.     

Growth hormone releasing hormone improves the cognition of healthy older adults

Declines in the activity of the somatotrophic axis have been implicated in the age-related changes observed in a number of physiological functions, including cognition. Such age-related changes may be arrested or partially reversed by hormonal supplementation. We examined the effect of 6 months treatment with daily growth hormone releasing hormone (GHRH) or placebo on the cognition of a group of 89 healthy older (68.0+/-0.7) adults. GHRH resulted in improved performance on WAIS-R performance IQ (p<0.01), WAIS-R picture arrangement (p<0.01), finding A's (p<0.01), verbal sets (p<0.01) and single-dual task (p<0.04). GHRH-based improvements were independent of gender, estrogen status or baseline cognitive capacity. These results demonstrate that the age-related decline in the somatotrophic axis may be related to age-related decline in cognition. Further they indicate that supplementation of this neuro-hormonal axis may partially ameliorate such cognitive declines in healthy normal older adults and potentially in individuals with impaired cognitive function (i.e., mild cognitive impairment and Alzheimer's disease).     

Anticipation of monetary gain but not loss in healthy older adults

Although global declines in structure have been documented in the aging human brain, little is known about the functional integrity of the striatum and prefrontal cortex in older adults during incentive processing. We used event-related functional magnetic resonance imaging to determine whether younger and older adults differed in both self-reported and neural responsiveness to anticipated monetary gains and losses. The present study provides evidence for intact striatal and insular activation during gain anticipation with age, but shows a relative reduction in activation during loss anticipation. These findings suggest that there is an asymmetry in the processing of gains and losses in older adults that may have implications for decision-making.     

Reproducibility of brain MRS in older healthy adults at 7T

To date, the majority of MRS reproducibility studies have been conducted in healthy younger adults, with only a few conducted in older adults at 3 T. With the growing interest in applying MRS methods to study the longitudinal course and effects of treatments in neurodegenerative disease, it is important to establish reproducibility in age‐matched controls, especially in older individuals. In this study, spectroscopic data were acquired using a stimulated echo acquisition mode (STEAM) localization technique in two regions (anterior and posterior cingulate cortices—ACC, PCC, respectively) in 10 healthy, cognitively normal older adults (64 ± 8.1 years). Reproducibility was assessed via mean coefficients of variation (CVs) and relative differences (RDs) calculated across two visits performed 2–3 months apart. Metabolites with high signal‐to‐noise ratio (SNR) such as NAA, tCho, and Glu had mean CVs of 10% or less and mean RDs of 15% or less across both regions. Metabolites with lower SNR such as GABA and Gln had slightly higher mean CVs of 22% or less and mean RDs of 27% or less across both regions. These results demonstrate the feasibility of acquiring MRS data at 7 T in older subjects, and establish that the spectroscopic data are reproducible in both the ACC and PCC in older, healthy subjects to the same extent as in previous studies in young subjects.     

Importance of optic flow for postural stability of male and female young adults

Purpose

A feedback control process based on self-motion perception contributes to postural stability; however, little is known about the visual modulation of postural muscles. The aim of this study was to investigate the effect of optic flow stimuli, presented full field, in the peripheral and foveal visual field, on muscular activation. Then, we assessed the correlation between optic flow, muscle activity and body sway in male and female subjects.

Methods

We used surface electromyography (EMG) and stabilometry on 24 right-handed young adults. We recorded the bilateral activation of tibialis anterior, gastrocnemius medialis, biceps femoris and vastus medialis. EMG and center of pressure (COP) signals were acquired simultaneously. EMG signal amplitude was computed as root mean square normalized by baseline.

Results

We found a significant effect for muscles, gender and an interaction effect of muscle by gender (ANOVA, p < 0.001). Results showed different postural alignments in males and females. The COP spatial variability during peripheral stimuli was generally reduced. The prevalent direction of oscillation evoked by peripheral stimuli was clustered, while foveal and random stimuli induced distributed and randomized directions. Also for muscle activity, we found gender differences in the prevalent oscillation distributions evoked by optic flow.

Conclusion

Visual stimuli always evoke an excitatory input on postural muscles, but the stimulus structure produces different postural effects. Peripheral optic flow stimuli stabilize postural sway, while random and foveal optic flow provoke larger sway variability similar to those evoked in the absence of visual stimulation.     

The effect of flow limitation on the cardiorespiratory response to arousal from sleep under controlled conditions of chemostimulation in healthy older adults

The influence of flow limitation on the magnitude of the cardiorespiratory response to arousal from sleep is of interest in older people, because they experience considerable flow limitation and frequent arousals from sleep. We studied older flow‐limiting subjects, testing the hypothesis that the cardiorespiratory activation response would be larger when arousal occurred during flow limitation, compared to no flow limitation, and chemical stimuli were controlled. In 11 older adults [mean ± standard deviation (SD) age: 68 ± 5 years] ventilation was stabilized using continuous positive airway pressure, and flow limitation was induced by dialling down the pressure. Partial pressure of end‐tidal carbon dioxide (PetCO₂) was maintained by titration of the inspired CO₂ and hyperoxia was maintained using 40% O₂ balanced with nitrogen. Flow limitation at the time of arousal did not augment cardiovascular activation response (heart rate P = 0.7; systolic blood pressure P = 0.6; diastolic blood pressure P = 0.3), whereas ventilation was greater following arousals during flow limitation compared to no flow limitation (P < 0.001). The pre–post‐arousal differences in ventilation reflected significant pre‐arousal suppression (due to flow limitation) plus post‐arousal activation. In summary, the cardiovascular response to arousal from sleep is not influenced by flow limitation at the time of arousal, when chemical stimuli are controlled in older adults. This finding may contribute to the decreased cardiovascular burden associated with sleep‐disordered breathing reported in older adults, although our data do not exclude the possibility that flow limitation in the presence of mild hypoxic hypercapnia could increase the cardiovascular response to arousal.     

Sex differences in delta and alpha EEG activities in healthy older adults

STUDY OBJECTIVES: To examine sex effects on sleep stages and electroencephalogram (EEG) spectral power in older adults. DESIGN: Sleep was polygraphically recorded for 2 consecutive nights, and blood was sampled during the last 24 hours. SETTING: The University of Chicago Clinical Research Center. PARTICIPANTS: Two groups of healthy nonobese older subjects: 10 men (59 +/- 2 years), and 10 postmenopausal women (63 +/- 2 years). INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: A spectral analysis of the EEG was performed in the delta and alpha bands. There were no sex differences in sleep stages. Blood sampling resulted in reductions of total sleep time, sleep maintenance, slow-wave sleep, and absolute delta activity that were all larger in women than in men. In absolute values, delta and alpha activities in non-rapid eye movement (NREM) and rapid eye movement (REM) sleep were higher in women than in men, but, for delta activity, the sex differences were larger in REM than in NREM sleep. In women, but not in men, absolute delta activity in REM was decreased during blood sampling and was strongly correlated with absolute delta activity in NREM. Delta activity in REM did not dissipate across the night in either group. When normalized for the activity in REM sleep, the sex difference in delta activity in NREM sleep was reversed, with lower activity in women. CONCLUSIONS: Sex differences in sleep EEG variables are present in older adults. When normalized, delta activity in older women is lower than in older men, which may be more consistent with sex differences in subjective complaints, in fragility of sleep in the presence of environmental disturbances, and in the relationship to growth-hormone release.     

Evidence for limb-independent control of locomotor trajectory

After stepping in place on a rotating treadmill, individuals exhibit involuntary turning in the direction opposite treadmill rotation when stepping in place on a stationary surface without vision. This response is called podokinetic after-rotation (PKAR). It remains unclear where the control center for PKAR is located and whether separate, independent podokinetic control centers exist for each lower limb. To better understand neural mechanisms underlying locomotor trajectory adaptation, this study asked whether PKAR transfers between lower limbs. Thirteen healthy adults underwent separate 15-min sessions where one (trained) leg or both legs stepped on the rotating surface. Afterward, all subjects exhibited PKAR during one-legged hopping on a stationary surface, whether hopping on the trained or untrained limb. There were no significant differences in mean turning velocity across conditions. Our results support the absence of independent podokinetic control centers for lower limbs, indicating that a single center may control locomotor trajectory.     

Markers of endothelial dysfunction and cerebral blood flow in older adults

We investigated the association of 2 markers of endothelial dysfunction, tissue plasminogen activator (t-PA) and Von Willebrand factor (VWF), with cerebral blood flow (CBF) in 541 older participants at high risk for cardiovascular disease. Serum levels of t-PA and VWF were measured at baseline. Participants underwent 2 successive brain magnetic resonance imaging scans, first at baseline and the then after a mean follow-up of 33 months. Total CBF was determined in each scan and also standardized for brain parenchymal volume. At baseline, higher t-PA was associated with lower CBF (p = 0.034). In the longitudinal analysis, higher levels of VWF were associated with a steeper decline in CBF (p = 0.043). There was no association between t-PA and decrease in CBF. These associations were independent of sociodemographic and cardiovascular factors. In conclusion, elevated markers of endothelial dysfunction are associated with lower CBF in older adults at risk for cardiovascular disease.     

Salivary cortisol, stress and mood in healthy older adults: the Zenith study

The aims of this study were to investigate the relationship between salivary cortisol, stress and mood and to look at the circadian rhythms of positive (PA) and negative (NA) mood in older adults. The participants were 41 healthy adults aged 55-69 years, recruited in Northern Ireland as part of the European Commission-funded Zenith project. Salivary cortisol samples were obtained twice a day (2.30 p.m. and 10.30 p.m.) for 7 consecutive days in conjunction with momentary measures of positive (PA) and negative mood (NA), using PANAS and a trait measure of perceived stress (Perceived Stress Scale). Salivary cortisol levels were measured using an enzyme-linked immunoassay kit. Higher perceived stress levels were associated with lower afternoon PA (r=-0.46, p=0.003) and higher afternoon (r=0.43, p=0.007) and evening (r=0.45, p=0.004) NA. Lower afternoon PA was correlated with higher evening cortisol concentrations (r=-0.47, p=0.002). Greater afternoon PA variability was associated with higher evening cortisol concentrations (r=0.38, p=0.015). A high intra-class correlation between cortisol and positive mood was found (r=0.67, p=0.009). Previously established rhythms for positive and negative mood were confirmed. Interestingly, there was no association between salivary cortisol levels and perceived stress in these healthy older adults. Further, more extensive research is required to better understand the apparent interplay between these variables and ageing.     

Resting EEG theta power correlates with cognitive performance in healthy older adults

We address the degree to which resting EEG bandpower is associated with cognitive performance in 73 healthy older adults (aged 56-70). Relative theta (4-6.5 Hz) power was significantly correlated with immediate and delayed verbal recall, attention, and executive function measures. Relative delta and alpha power and peak alpha frequency did not correlate with any cognitive measures. These data indicate that high resting theta power in healthy older adults is associated with better cognitive function and may be a marker of healthy neurocognitive aging. Comparison of these with previous findings suggests that two forms of theta-frequency oscillations may exist; one indicative of healthy neurocognitive function and the other, EEG/alpha slowing linked to (future) substantial cognitive decline. Future EEG investigations of cognitive aging or decline should analyze both relative theta power and degree of EEG/alpha slowing so as not to confound these.     

Blunted cardiac autonomic responsiveness to hypoxemic stress in healthy older adults.

Supine resting cardiac dynamics and responses to steady-state hypoxemia were investigated in six healthy older (59-72 yrs) adults using coarse-graining spectral analysis of heart rate variability (HRV) and were compared to six young (22-29 yrs) adults studied previously (Lucy et al., 2000). End-tidal carbon dioxide pressure (PETCO2) was clamped at 1-2 mmHg above the usual resting value for 11 min of euoxia (PETO2 100 mmHg), followed by 22 min of hypoxia (PETO2 55 mmHg). During euoxia, vagally mediated harmonic and fractal power of HRV of older adults was minimal. Hypoxia induced an increase in ventilation, p < 0.01, and heart rate, p < 0.05. The heart rate increase (mean +/- SE) of 0.23 +/- 0.08 beats.min-1 per 1% decrease in arterial O2 saturation was 25% of that demonstrated previously by young subjects, p < 0.001. In older adults, HRV spectral power remained unchanged during hypoxia, providing further evidence of an age-related blunting of cardiac autonomic function.     

Preceding stimulus sequence effects on the oddball-P300 in young and healthy older adults

The present study examined the mechanisms underlying stimulus sequence effects on the parietal P300 and frontal P3a elicited by infrequent targets in an oddball paradigm and compared these effects between young and older adults. Fifty young and 50 healthy older adults completed a simple visual oddball task including an infrequent (20%) target stimulus. A temporo-spatial principal component (PCA) analysis was used to disentangle the parietal P300 and frontal P3a from overlapping ERP components. The typical age-related anterior-shift of the P300 was, according to the PCA, due to a disproportionately large contribution of a frontal P3a in older adults. Up to about five successive standards preceding a target, the results replicated the typical increase in parietal P300 amplitude to targets with increases in preceding standards. A novel finding was that with further increases in preceding standards, P300 amplitude to targets gradually decreased. This pattern is consistent with a combination of relatively automatic, temporary expectations and higher level, conscious expectations driving P300 sequential effects, with different dynamics over the course of successively presented standards. However, an expectancy-based account of these sequential effects was challenged by an analogous analysis of RTs. Sequential effects on the frontal P3a differed from the parietal P300: The P3a was largest when a target followed another target and continually decreased with the number of intervening standards. Notably, sequential effects were strikingly similar for young and older adults, and implications for the functional significance of morphological changes in P300 due to aging are discussed.     

Intraindividual variability in cognitive performance in older adults: comparison of adults with mild dementia, adults with arthritis, and healthy adults

Intraindividual variability in latency and accuracy of cognitive performance across both trials and occasions was examined in 3 groups of older adults: healthy adults, adults with arthritis, and adults diagnosed with mild dementia. Participants completed 2 reaction-time and 2 episodic-memory tasks on 4 occasions. Results indicated that intraindividual variability in latency was greater in individuals diagnosed with mild dementia than in adults who were neurologically intact, regardless of their health status. Individual differences in variability were stable over time and across cognitive domains. Intraindividual variability was also related to level of performance and was uniquely predictive of neurological status, independent of level of performance. Results suggest that intraindividual variability may be a behavioral indicator of compromised neurological mechanisms.     

A systematic literature review and meta-analysis of real-world interventions for cognitive ageing in healthy older adults

Activities running in community-based-settings offer a method of delivering multimodal interventions to older adults beyond cognitive training programmes. This systematic review and meta-analysis investigated the impact of randomised controlled trials (RCTs) of ‘real-world’ interventions on the cognitive abilities of healthy older adults. Database searches were performed between October 2016 and September 2018. Forty-three RCTs were eligible for inclusion with 2826 intervention participants and 2234 controls. Interventions to enhance cognitive ability consisted of participation in activities that were physical (25 studies), cognitive (9 studies), or mixed (i.e., physical and cognitive; 7 studies), and two studies used other interventions that included older adults assisting schoolchildren and engagement via social network sites. Meta-analysis revealed that Trail Making Test (TMT) A, p = 0.05, M = 0.43, 95% CI [-0.00, 0.86], digit symbol substitution, p = 0.05, M = 0.30, 95% CI [0.00, 0.59], and verbal fluency, p = 0.04, M = 0.31, 95% CI [0.02, 0.61], improved after specific types of interventions versus the control groups (which were either active, wait-list or passive controls). When comparing physical activity interventions against all control groups, TMT A, p = 0.04, M = 0.25, 95% CI [0.01, 0.48], and digit span forward, p = 0.05, M = 0.91, 95% CI [-0.00, 1.82], significantly improved. Results remained non-significant for all outcomes when comparing cognitive activity interventions against all control groups. Results therefore suggest that healthy older adults are more likely to see cognitive improvements when involved in physical activity interventions. In addition, TMT A was the only measure that consistently showed significant improvements following physical activity interventions. Visuospatial abilities (as measured by TMT A) may be more susceptible to improvement following physical activity-based interventions, and TMT A may be a useful tool for detecting differences in that domain.