Niacin modulates macrophage polarization in Parkinson's disease.

Neuroinflammation remains a central piece in Parkinson's disease (PD) pathophysiology. However, mechanisms by which PD links to the neuroinflammation remain elusive. Here, for the first time, we report that lower dose of niacin in PD patients may affect macrophage polarization from M1 (pro-inflammatory) to M2 (counter-inflammatory) profile through the niacin receptor GPR109A. Skew in the peripheral macrophages were accompanied by improved quality of life assessments in patients. Low dose niacin supplementation may be beneficial in PD, boosting anti-inflammatory processes and suppressing inflammation. Varied niacin dosages for longer durations may further reveal the potential role of anti-inflammatory interventions in PD progression.

Two Mechanisms of Sensorimotor Set Adaptation to Inclined Stance.

Orientation of posture relative to the environment depends on the contributions from the somatosensory, vestibular, and visual systems mixed in varying proportions to produce a sensorimotor set. Here, we probed the sensorimotor set composition using a postural adaptation task in which healthy adults stood on an inclined surface for 3 min. Upon returning to a horizontal surface, participants displayed a range of postural orientations - from an aftereffect that consisted of a large forward postural lean to an upright stance with little or no aftereffect. It has been hypothesized that the post-incline postural change depends on each individual's sensorimotor set: whether the set was dominated by the somatosensory or vestibular system: Somatosensory dominance would cause the lean aftereffect whereas vestibular dominance should steer stance posture toward upright orientation. We investigated the individuals who displayed somatosensory dominance by manipulating their attention to spatial orientation. We introduced a distraction condition in which subjects concurrently performed a difficult arithmetic subtraction task. This manipulation altered the time course of their post-incline aftereffect. When not distracted, participants returned to upright stance within the 3-min period. However, they continued leaning forward when distracted. These results suggest that the mechanism of sensorimotor set adaptation to inclined stance comprises at least two components. The first component reflects the dominant contribution from the somatosensory system. Since the postural lean was observed among these subjects even when they were not distracted, it suggests that the aftereffect is difficult to overcome. The second component includes a covert attentional component which manifests as the dissipation of the aftereffect and the return of posture to upright orientation.

Hysteresis in Center of Mass Velocity Control during the Stance Phase of Treadmill Walking.

Achieving a soft landing during walking can be quantified by analyzing changes in the vertical velocity of the body center of mass (CoM) just prior to the landing of the swing limb. Previous research suggests that walking speed and step length may predictably influence the extent of this CoM control. Here we ask how stable this control is. We altered treadmill walking speed by systematically increasing or decreasing it at fixed intervals. We then reversed direction. We hypothesized that the control of the CoM vertical velocity during the late stance of the walking gait may serve as an order parameter which has an attribute of hysteresis. The presence of hysteresis implies that the CoM control is not based on simply knowing the current input conditions to predict the output response. Instead, there is also the influence of previous speed conditions on the ongoing responses. We found that the magnitudes of CoM control were different depending on whether the treadmill speed (as the control parameter) was ramped up or down. Changes in step length also influenced CoM control. A stronger effect was observed when the treadmill speed was speeded up compared to down. However, the effect of speed direction remained significant after controlling for step length. The hysteresis effect of CoM control as a function of speed history demonstrated in the current study suggests that the regulation of CoM vertical velocity during late stance is influenced by previous external conditions and constraints which combine to influence the desired behavioral outcome.

Specific interference between a cognitive task and sensory organization for stance balance control in healthy young adults: visuospatial effects.

We tested the hypothesis that a computational overload results when two activities, one motor and the other cognitive that draw on the same neural processing pathways, are performed concurrently. Healthy young adult subjects carried out two seemingly distinct tasks of maintaining standing balance control under conditions of low (eyes closed), normal (eyes open) or high (eyes open, sway-referenced surround) visuospatial processing load while concurrently performing a cognitive task of either subtracting backwards by seven or generating words of the same first letter. A decrease in the performance of the balance control task and a decrement in the speed and accuracy of responses were noted during the subtraction but not the word generation task. The interference in the subtraction task was isolated to the first trial of the high but not normal or low visuospatial conditions. Balance control improvements with repeated exposures were observed only in the low visuospatial conditions while performance in the other conditions remained compromised. These results suggest that sensory organization for balance control appear to draw on similar visuospatial computational resources needed for the subtraction but not the word generation task. In accordance with the theory of modularity in human performance, the contrast in results between the subtraction and word generation tasks suggests that the neural overload is related to competition for similar visuospatial processes rather than limited attentional resources.

Age-related changes in the center of mass velocity control during walking.

During walking, the body center of mass oscillates along the vertical plane. Its displacement is highest at mid-swing and lowest at terminal swing during the transition to double support. Its vertical velocity (CoMv) has been observed to increase as the center of mass falls between mid- and late swing but is reduced just before double support. This suggests that braking of the center of mass is achieved with active neural control. We tested whether this active control deteriorates with aging (Experiment 1) and during a concurrent cognitive task (Experiment 2). At short steps of <0.4m, CoMv control was low and similar among all age groups. All groups braked the CoMv at longer steps of >0.4m but older subjects did so to a lesser extent. During the cognitive task, young subjects increased CoMv control (i.e. increase in CoMv braking) while maintaining step length and walking speed. Older subjects on the other hand, did not increase CoMv control but rather maintain it by reducing both step length and walking speed. These results suggest that active braking of the CoM during the transition to double support predominates in steps >0.4m. It could be a manifestation of the balance control system, since the braking occurs at late stance where body weight is being shifted to the contralateral side. The active braking mechanism also appears to require some attentional resource. In aging, reducing step length and speed are strategic to maintaining effective center of mass control during the transition to double support. However, the lesser degree of control in older adults indicates a true age-related deficit.

An instance of reduced center of mass displacement: the Ba Gua Zhang walking gait.

The Ba Gua Zhang walking gait was examined in an accomplished practitioner to test the hypothesis that reducing the vertical oscillation of the body center of mass (CoM) conserves energy. Compared to typical walking, center-of-mass displacement and peak vertical ground reaction force decreased during Ba Gua Zhang walking. Muscle activity in the lower extremities and lower back, however, increased. The results failed to support the concept of decreasing CoM oscillations to increase efficiency.

Factor analysis of the functional limitations test in healthy individuals.

The NeuroCom's Functional Limitations test evaluates motor performances on various dynamic movements but it is not known how the outcome variables among these movements might be related to each other. An exploratory factor analysis was conducted in healthy young individuals to identify the dimensions that contribute to the overall variance associated with the variables in the test items. Six factors comprising 18 out of 24 variables explained 76% of the overall variance. Variables from within a test item tended to be grouped in the same factor, suggesting that each item evaluates a particular set of motor skills that is required to execute the movement. The results suggest that all six items of the Functional Limitations test should to be used to estimate the overall functional motor control performance of an individual. The normative data gathered in this study using healthy individuals will allow us to compare individuals with movement limitations.

Comparison of muscle functions during three contrasting abdominal exercises.

That different amplitudes of muscle activities during various abdominal exercises not only reflect the inherent differences in motor control but movement speed as well was hypothesized. 20 healthy adults (M age = 23 yr.) performed three exercises that involved varying amounts of trunk control: the partial sit-up, full sit-up, and AbSlide roll. Covariate analyses indicated that the amplitude of muscle activities could be partitioned into three categories: motor control and scaling (speed and amplitude), scaling only, and motor control only. Overall, the AbSlide exercise activated the most amount of muscular activity, followed by the full and partial sit-up exercises. Results are discussed in terms of how the various muscles contribute to motor control and velocity scaling.

Interaction between transient change in local muscle structure and segmented leg motor responses.

We investigated the interaction between transient change in the local structure of gastrocnemius muscle fibers and the segmented leg motor responses elicited by toes-up rotation of the support surface. The gastrocnemius muscle in healthy young subjects underwent a sustained 2-min, isometric stretch (Prestretch group), followed immediately by the rotations. Analysis showed that the prestretch affected the amplitude of the monosynaptic but not the automatic components of the medial gastrocnemius muscle responses (monosynaptic response: 93 +/- 20% of the mean of the last three rotations in the Prestretch group compared to 174 +/- 42% in the Control group; automatic response: 128 +/- 18% in the Prestretch group versus 123 +/- 31% in the Control group). The shortened tibialis anterior muscle response and the onset latencies of responses were not affected by prestretching the gastrocnemius muscle. The prestretch effect on the amplitude of the monosynaptic (mediated by group Ia afferents) but not the automatic gastrocnemius muscle response (mediated by group II afferents) suggests that the automatic component of the muscle response to platform rotations has a stronger supraspinal influence than the monosynaptic response and is thus less affected by local events such as prolonged stretching.