Brad Manor

Physiological complexity and system adaptability: evidence from postural control dynamics of older adults

The degree of multiscale complexity in human behavioral regulation, such as that required for postural control, appears to decrease with advanced aging or disease. To help delineate causes and functional consequences of complexity loss, we examined the effects of visual and somatosensory impairment on the complexity of postural sway during quiet standing and its relationship to postural adaptation to cognitive dual tasking. Participants of the MOBILIZE Boston Study were classified into mutually exclusive groups: controls [intact vision and foot somatosensation, n = 299, 76 ± 5 (SD) yr old], visual impairment only (<20/40 vision, n = 81, 77 ± 4 yr old), somatosensory impairment only (inability to perceive 5.07 monofilament on plantar halluxes, n = 48, 80 ± 5 yr old), and combined impairments (n = 25, 80 ± 4 yr old). Postural sway (i.e., center-of-pressure) dynamics were assessed during quiet standing and cognitive dual tasking, and a complexity index was quantified using multiscale entropy analysis. Postural sway speed and area, which did not correlate with complexity, were also computed. During quiet standing, the complexity index (mean ± SD) was highest in controls (9.5 ± 1.2) and successively lower in the visual (9.1 ± 1.1), somatosensory (8.6 ± 1.6), and combined (7.8 ± 1.3) impairment groups (P = 0.001). Dual tasking resulted in increased sway speed and area but reduced complexity (P < 0.01). Lower complexity during quiet standing correlated with greater absolute (R = -0.34, P = 0.002) and percent (R = -0.45, P < 0.001) increases in postural sway speed from quiet standing to dual-tasking conditions. Sensory impairments contributed to decreased postural sway complexity, which reflected reduced adaptive capacity of the postural control system. Relatively low baseline complexity may, therefore, indicate control systems that are more vulnerable to cognitive and other stressors.

The Nonlinear Relationship Between Gait Speed and Falls: The Maintenance of Balance, Independent Living, Intellect, and Zest in the Elderly of Boston Study

OBJECTIVES: To examine the relationship between gait speed and falls risk.

Enhancement of Vasoreactivity and Cognition by Intranasal Insulin in Type 2 Diabetes

OBJECTIVE To determine acute effects of intranasal insulin on regional cerebral perfusion and cognition in older adults with type 2 diabetes mellitus (DM). RESEARCH DESIGN AND METHODS This was a proof-of-concept, randomized, double-blind, placebo-controlled intervention evaluating the effects of a single 40-IU dose of insulin or saline on vasoreactivity and cognition in 15 DM and 14 control subjects. Measurements included regional perfusion, vasodilatation to hypercapnia with 3-Tesla MRI, and neuropsychological evaluation. RESULTS Intranasal insulin administration was well tolerated and did not affect systemic glucose levels. No serious adverse events were reported. Across all subjects, intranasal insulin improved visuospatial memory (P ≤ 0.05). In the DM group, an increase of perfusion after insulin administration was greater in the insular cortex compared with the control group (P = 0.0003). Cognitive performance after insulin administration was related to regional vasoreactivity. Improvements of visuospatial memory after insulin administration in the DM group (R2adjusted = 0.44, P = 0.0098) and in the verbal fluency test in the control group (R2adjusted = 0.64, P = 0.0087) were correlated with vasodilatation in the middle cerebral artery territory. CONCLUSIONS Intranasal insulin administration appears safe, does not affect systemic glucose control, and may provide acute improvements of cognitive function in patients with type 2 DM, potentially through vasoreactivity mechanisms. Intranasal insulin-induced changes in cognitive function may be related to vasodilatation in the anterior brain regions, such as insular cortex that regulates attention-related task performance. Larger studies are warranted to identify long-term effects and predictors of positive cognitive response to intranasal insulin therapy.

Physiologic complexity and aging: implications for physical function and rehabilitation.

The dynamics of most healthy physiological processes are complex, in that they are comprised of fluctuations with information-rich structure correlated over multiple temporospatial scales. Lipsitz and Goldberger (1992) first proposed that the aging process may be characterized by a progressive loss of physiologic complexity. We contend that this loss of complexity results in functional decline of the organism by diminishing the range of available, adaptive responses to the innumerable stressors of everyday life. From this relationship, it follows that rehabilitative interventions may be optimized by targeting the complex dynamics of human physiology, and by quantifying their effects using tools derived from complex systems theory. Here, we first discuss several caveats that one must consider when examining the functional and rehabilitative implications of physiologic complexity. We then review available evidence regarding the relationship between physiologic complexity and system functionality, as well as the potential for interventions to restore the complex dynamics that characterize healthy physiological function.

Adhesion Molecules, Altered Vasoreactivity, and Brain Atrophy in Type 2 Diabetes

OBJECTIVE To investigate the effects of inflammation on perfusion regulation and brain volumes in type 2 diabetes. RESEARCH DESIGN AND METHODS A total of 147 subjects (71 diabetic and 76 nondiabetic, aged 65.2 ± 8 years) were studied using 3T anatomical and continuous arterial spin labeling magnetic resonance imaging. Analysis focused on the relationship between serum soluble vascular and intercellular adhesion molecules (sVCAM and sICAM, respectively, both markers of endothelial integrity), regional vasoreactivity, and tissue volumes. RESULTS Diabetic subjects had greater vasoconstriction reactivity, more atrophy, depression, and slower walking. Adhesion molecules were specifically related to gray matter atrophy (P = 0.04) and altered vasoreactivity (P = 0.03) in the diabetic and control groups. Regionally, sVCAM and sICAM were linked to exaggerated vasoconstriction, blunted vasodilatation, and increased cortical atrophy in the frontal, temporal, and parietal lobes (P = 0.04–0.003). sICAM correlated with worse functionality. CONCLUSIONS Diabetes is associated with cortical atrophy, vasoconstriction, and worse performance. Adhesion molecules, as markers of vascular health, have been indicated to contribute to altered vasoregulation and atrophy.

Long Term Tai Chi Exercise Improves Physical Performance Among People with Peripheral Neuropathy

This study examined the effects of a 24-week Tai Chi intervention on physical function in individuals with peripheral neuropathy. Twenty-five women and men with peripheral neuropathy were recruited. Plantar pressure detection threshold was assessed with a 5.07 gauge monofilament. Functional gait was assessed by the 6-min walk and timed up-and-go tests. Isokinetic leg strength and standing balance was also assessed. Twenty-four consecutive weeks of modified, group-based Tai Chi practice was completed, with testing repeated every six weeks throughout. No adverse events were observed and attendance was 17 +/- 4 sessions per 6 weeks. After 6 weeks of Tai Chi, participants increased 6-min walk (P < 0.0001), timed up-and-go (P < 0.0001), and leg strength (P < 0.01) performance. Continued improvement was observed in the timed up-and-go. Plantar sensation improved (P = 0.003) following the Tai Chi intervention. Group-based Tai Chi is a safe, plausible, and effective intervention for those with PN.

Stance and sensory feedback influence on postural dynamics

This study examined the effects of ice-induced plantar desensitization and the withdrawal of visual feedback on the magnitude and time-dependent structure of postural sway variability. The magnitude of variability was quantified as the area of an ellipse enclosing 95% of the center of pressure (COP) time-series during normal and tandem stances. The same time-series were also analyzed using Approximate Entropy (ApEn) and Cross-Approximate Entropy (CrossApEn) as indices of irregularity and asynchrony between the mediolateral and anteroposterior COP motions. Variability increased during tandem stance and this increase was compounded by both visual feedback withdrawal and cutaneous desensitization. Both ApEn (mediolateral and anteroposterior COP motion) and CrossApEn increased with the withdrawal of visual feedback during the tandem stance, but decreased significantly during normal stance. The results of the study demonstrate that plantar desensitization only affected the magnitude of sway variability but did not alter its time-dependent structure. Contrasting effects on the structure of postural sway variability with visual feedback withdrawal were observed during the different stances, highlighting the role of task demands in postural dynamics.

Quantitative cerebral blood flow mapping and functional connectivity of postherpetic neuralgia pain: A perfusion fMRI study

Summary This study investigated the postherpetic neuralgia pain‐related brain regions and the underlying seed‐based networks detected by arterial spin labeling. Abstract This article investigates the effects of postherpetic neuralgia (PHN) on resting‐state brain activity utilizing arterial spin labeling (ASL) techniques. Features of static and dynamic cerebral blood flow (CBF) were analyzed to reflect the specific brain response to PHN pain. Eleven consecutive patients suffering from PHN and 11 age‐ and gender‐matched control subjects underwent perfusion functional magnetic resonance imaging brain scanning during the resting state. Group comparison was conducted to detect the regions with significant changes of CBF in PHN patients. Then we chose those regions that were highly correlated with the self‐reported pain intensity as “seeds” to calculate the functional connectivity of both groups. Absolute CBF values of these regions were also compared across PHN patients and control subjects. Significant increases in CBF of the patient group were observed in left striatum, right thalamus, left primary somatosensory cortex (S1), left insula, left amygdala, left primary somatomotor cortex, and left inferior parietal lobule. Significant decreases in CBF were mainly located in the frontal cortex. Regional CBF in the left caudate, left insula, left S1, and right thalamus was highly correlated with the pain intensity, and further comparison showed that the regional CBF in these regions is significantly higher in PHN groups. Functional connectivity results demonstrated that the reward circuitry involved in striatum, prefrontal cortex, amygdala, and parahippocampal gyrus and the circuitry among striatum, thalamus, and insula were highly correlated with each element in PHN patients. In addition, noninvasive brain perfusion imaging at rest may provide novel insights into the central mechanisms underlying PHN pain.

Advanced BrainAGE in older adults with type 2 diabetes mellitus

Aging alters brain structure and function and diabetes mellitus (DM) may accelerate this process. This study investigated the effects of type 2 DM on individual brain aging as well as the relationships between individual brain aging, risk factors, and functional measures. To differentiate a pattern of brain atrophy that deviates from normal brain aging, we used the novel BrainAGE approach, which determines the complex multidimensional aging pattern within the whole brain by applying established kernel regression methods to anatomical brain magnetic resonance images (MRI). The “Brain Age Gap Estimation” (BrainAGE) score was then calculated as the difference between chronological age and estimated brain age. 185 subjects (98 with type 2 DM) completed an MRI at 3Tesla, laboratory and clinical assessments. Twenty-five subjects (12 with type 2 DM) also completed a follow-up visit after 3.8 ± 1.5 years. The estimated brain age of DM subjects was 4.6 ± 7.2 years greater than their chronological age (p = 0.0001), whereas within the control group, estimated brain age was similar to chronological age. As compared to baseline, the average BrainAGE scores of DM subjects increased by 0.2 years per follow-up year (p = 0.034), whereas the BrainAGE scores of controls did not change between baseline and follow-up. At baseline, across all subjects, higher BrainAGE scores were associated with greater smoking and alcohol consumption, higher tumor necrosis factor alpha (TNFα) levels, lower verbal fluency scores and more severe deprepession. Within the DM group, higher BrainAGE scores were associated with longer diabetes duration (r = 0.31, p = 0.019) and increased fasting blood glucose levels (r = 0.34, p = 0.025). In conclusion, type 2 DM is independently associated with structural changes in the brain that reflect advanced aging. The BrainAGE approach may thus serve as a clinically relevant biomarker for the detection of abnormal patterns of brain aging associated with type 2 DM.

Characteristics of Functional Gait among People with and without Peripheral Neuropathy

UNLABELLED It is advantageous from a rehabilitation standpoint to determine physiological factors associated with functional gait. These factors may be fundamentally different in those with peripheral neuropathy (PN) compared to age-matched healthy individuals. The purpose of this investigation was to examine associations between functional gait and measures of leg strength, standing balance, and locomotor kinematics in people with and without PN. METHODS Individuals with PN and age-matched controls were assessed for functional gait by the 6-min walk and timed up-and-go tests. Leg strength was measured as isokinetic peak torque of the knee extensors. Standing balance was assessed by center-of-pressure sway velocity and area during quiet stance. Locomotor kinematics from treadmill walking were used to compute stride duration variability and local instability (i.e., finite-time Lyapunov exponents), which estimate kinematic divergence caused by small-scale perturbations. RESULTS Leg strength and locomotor kinematics - in particular local instability - correlated with functional gait performance in controls. Conversely, reduced functional gait performance in the PN group was primarily mediated by impaired standing balance control. DISCUSSION Locomotor kinematics predicts functional gait, and the magnitude of variability and local instability should be calculated to fully evaluate locomotor system health. The observation that different factors associated with functional gait between groups speaks to the uniqueness of the PN-related movement disorder. Functional gait-related rehabilitation programs for PN patients should be tailored toward this uniqueness.