School of Public Health

Permanent URI for this communityhttp://hdl.handle.net/1903/1633

The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

Note: Prior to July 1, 2007, the School of Public Health was named the College of Health & Human Performance.

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Subject: search.filters.subject.Biology, Neuroscience

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Now showing 1 - 10 of 10
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    Probing Postural Stability Mechanisms in Locomotion
    (2009) Logan, David Michael; Jeka, John J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    It is not currently known if those upright stability mechanisms utilized in standing posture are present in locomotion. In this investigation, subjects walked or stood on a treadmill in three speed conditions (posture, 1 km/h, 5 km/h) in front of a visual scene consisting of randomly oriented triangles. The triangles translated in the Anterior-Posterior (A/P) direction in either a low or high amplitude condition. Frequency response functions (FRFs) of both the A/P displacement of bilateral kinematic markers and their corresponding segment angles in response to the visual scene translations were computed. Gain and phase of these FRFs had consistent responses in high amplitude visual conditions in the trunk (hip and shoulder displacements, trunk angle), which motivated further comparisons within the trunk during posture and locomotion. In doing so, the postural processes of orientation and equilibrium control were teased apart during locomotion.
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    Retention of a novel visuomotor gain in patients with Parkinson's disease is context-specific
    (2009) Venkatakrishnan, Anusha; Contreras-Vidal, José L; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hypometria or reduced movement amplitude is a major concern in Parkinson's disease (PD) since it impairs multiple functional activities of daily living, including fine motor control tasks, such as handwriting. Recent research using virtual or computer-based environments, wherein visual information about hand movement is altered and dissociated from perception (e.g., position sense or kinesthesia) of hand movement itself, has shown increases in handwriting size in patients with PD. In fact, preliminary findings in our laboratory have shown that gradual alterations in visual feedback of movement facilitate adaptation of handwriting size in patients with PD, plausibly by recruiting neural networks other than the basal ganglia, such as those in cerebellum. The purpose of this study was to determine whether these adaptive effects persist after a week following visuomotor training in patients with PD and can favorably transfer to other functional writing and drawing tasks. Thirteen patients with Parkinson's disease and twelve healthy, age-matched subjects practiced handwriting either under gradually manipulated (intervention) or intact (placebo) visual display of handwriting size. The results from this study show for the first time, that these adaptive effects may persist for at least up to a week in PD; however, a single training session seemed inadequate to transfer these acquired changes to paper-pen writing and drawing. Additionally, experimental manipulation of task demands during training also helped maintain movement quality in patients with PD as against the placebo group. These findings have important implications in designing rehabilitative interventions to enhance functional sensorimotor performance in patients with PD.
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    Handwriting Kinetics: A Search for Synergies
    (2008) Hooke, Alexander W.; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of this study was to investigate central nervous system strategies for controlling multi-finger forces in three-dimensional (3-D) space during a circle drawing task. In order to do this the Kinetic Pen, a pen capable of measuring the six-component force and moment of force that each of four individual contacts applies to the pen during writing, was developed. The synergistic actions of the contact forces, defined as kinetic synergy, were investigated in three orthogonal spaces: radial, tangential, and vertical to the circle edge during a circle drawing task. We employed varying directional (clockwise vs. counterclockwise) and pacing (self-paced vs. external-paced) conditions. Results showed that synergies between pen-hand contact forces existed in all components. Radial and tangential component synergies were greater than in the vertical component. Synergies in the clockwise direction were stronger than the counter-clockwise direction in the radial and vertical components. Pace was found to be insignificant in all conditions.
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    Sensory-Related Changes in Two-Segment Dynamics on a Sway-Referenced Support Surface
    (2008-11-19) Creath, Robert Andrew; Jeka, John J; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In its simplest form, the human postural control system can be described as a closed-loop control system consisting of a plant (body segments and musculotendon actuators) and feedback. Previous efforts to understand the contributions of plant and feedback employed techniques to "open the loop" which is problematic with the study of posture because the plant is unstable without feedback. In the present experiment, a closed-loop system identification method was used to "open the loop" without removal of sensory feedback. Subjects stood on a movable platform facing a visual scene, both of which were capable of rotation about an axis coaxial with the subject's ankles. The visual stimulus (present all trials) consisted of a 10-frequency sum-of-sines while movement of the support surface consisted of the following conditions: 1. Stationary; 2. Sway-referenced to the subject's body sway; 3. 10-frequency sum-of-sines; 4. Combined sway-referenced and sum-of-sines. Closed-loop frequency response functions were calculated for visual stimulus to EMG and visual stimulus to body sway angle. The open loop frequency response function for the plant was determined by dividing the frequency response functions, mathematically canceling the effects of feedback. With respect to the visual stimulus, gains for the leg segment showed no differences between the four platform conditions. Phase for the stationary condition was lower at the higher stimulus driving frequencies than for any of the moving platform conditions. In contrast, trunk segment gains were lower for the sway-referenced conditions at lower stimulus frequencies than for the stationary and sum-of-sines conditions. Phase showed a slight lead of the legs over the trunk for the sway-referenced conditions. The phase relationship between the trunk and leg segments, typically in-phase below ~1 Hz and anti-phase above ~1 Hz, showed a gradual transition at a lower frequency for the sway-referenced conditions than for the stationary or sum-of-sines conditions. Complex coherence showed a "legs-leading" coordinative relationship at the phase mode transition for the two sway-referenced conditions. Differences in the frequency response functions demonstrate that the plant changes with platform condition requiring different postural control strategies to maintain stability.
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    Effect of kinetic degrees of freedom in multi-finger force and moment stabilizing synergies.
    (2008-09-02) Karol, Sohit; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The purpose of the present study was to test the principle of motor abundance as compared to motor redundance, by investigating the changes in force stabilizing and moment stabilizing synergies for pressing tasks involving different number of fingers (IM, IR, IL, MR, ML, RL, IMR, IML, IRL, MRL, IMRL; where I=Index, M=Middle, R=Ring, L=Little). Twelve healthy right-handed subjects (6 males and 6 females, 27 4.3 years) participated in the experiment. Subjects were explicitly provided a visual feedback of forces for a constant multi finger force production task. Since subjects were explicitly given a visual feedback of their performance for the force production task, strong force stabilizing synergies were expected (Hypothesis 1). Based on the principle of abundance, we hypothesized that the force stabilizing synergies would increase with the number of fingers (Hypothesis 2). Assuming that the precise moment stabilizing synergies are conditioned by everyday prehension experiences, we hypothesized that moment stabilizing synergies, if existing, would increase with the number of fingers, since all the fingers are generally used for everyday prehension and manipulation tasks, and such tasks require a precise control of moments (Hypothesis 3). Also, if both the synergies existed simultaneously, we hypothesized that those synergies would be more prominent when more fingers are involved in the task (Hypothesis 4).It was found that strong force stabilizing synergies existed for all the finger combinations, thus confirming our first hypothesis. However, these force stabilizing synergies reduced with an increase in the number of task fingers, disproving our second hypothesis. Moment destabilizing synergies were found for the two finger combinations and no moment synergies were present for the three finger combinations. However, moment stabilizing synergies existed for the four finger combinations. This confirmed our third and fourth hypothesis. We interpret the findings an evidence for the principle of abundance for stabilization of moments during pressing tasks, regardless of the fact that only the visual feedback of forces was given to the subjects.
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    On the Development of Postural Stability During Infancy as a Process of Growth and Active, Exploratory Sensorimotor Tuning
    (2007-12-04) Metcalfe, Jason Scott; Clark, Jane E; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The process by which humans stabilize bipedal stance represents a confluence of changes associated with musculoskeletal maturation and experience-based sensorimotor learning. While investigations have documented a variety of changes with increased bipedal experience, such as reduced velocity and frequency of postural sway and concomitant refinements in muscle activation sequences, the extent to which these changes may be ascribed to growth versus learning processes has not been well characterized. For example, reduced sway frequency is a natural consequence of increasing body height but alternatively, may be explained by active modulations in motor commands specifying the timing and magnitude of muscular activation sequences. It is clear that both types of influences are needed to explain postural development. However, a parsimonious framework for understanding and explaining postural development has yet to be clearly articulated and validated against empirical observations. As such, the purpose of this dissertation was to initiate the development of such an account through a combination of empirical and computational studies. In this dissertation, data are presented from a longitudinal study of upright posture in infants ranging from the onset of independent sitting until 9 months of walking experience; this dissertation focused on the particular period spanning from walk onset onward. Infants participated in a quiet stance task involving hand contact with a surface that was either static or dynamic as well as an independent stance condition. Empirical analyses were performed to estimate the statistical properties of sway and characterize adaptations to static and dynamic manipulations utilizing the touch surface. An unexpected lack of significance for sway magnitude was observed in all conditions. Robust effects, however, were found across measures of rate properties of sway. Taken in the context of previous literature, the empirical observations were used to guide a final study utilizing computational techniques to test hypotheses regarding potential sources of change in postural development. First, the mechanical and computational requirements for postural stabilization were systematically assessed through a review of extant models of both stance and motor learning. Armed with insights from this review, the final study examined an autonomous reinforcement learning algorithm, that was designed to capture the essence of how a human may stabilize his or her posture under the tutelage of exploratory action. Simulation results provided evidence in support of conclusions regarding changes in rate-properties of postural sway and underlying associations with physical growth as well as calibration of both sensory and motor system parameters. Further, simulations emphasized the importance of inclusion of noise in biologically-relevant aspects of the model, such as in sensory and motor processes, as well as the need to consider physical morphology as a primary constraint on sensorimotor learning in the context of upright postural development.
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    The Relationship Between Exercise and Cognitive Function: Is It Altered by APOE Genotype?
    (2006-12-11) Conery, Ryan; Hatfield, Brad D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The risk of minor cognitive decline and dementia increases with advancing age. Thus, as the average lifespan of humans continues to rise the number of people that are affected by dementia will rapidly increase. Dementia is described as multiple cognitive deficits that adversely impact activities of daily living. Lifestyle behaviors may prove critical in delaying or preventing the onset of cognitive decline and dementia. Specifically, exercise has been shown to decrease reaction time, improve executive function, and maintain performance on gross measures of cognitive ability in an aging population. Further, physical activity becomes even more important when the genetic susceptibility for dementia rises. Apolipoprotein (APOE) e4 is one such risk factor and is associated with the development of Alzheimer's disease (AD). Severe memory loss is one defining symptom of AD and greatly reduces quality of life for afflicted individuals. The purpose of this investigation is to determine the specific behavioral impact of physical activity on those who are genetically at risk for AD compared to those who are not. Sixty cognitively normal individuals between 50 - 70 years old were assessed on medical history, gross cognitive function, physical activity, memory performance (Sternberg memory task), executive control function (Eriksen flanker task), and finally APOE genotype. Using hierarchical regression techniques, memory and executive function scores were regressed on age, education, genotype, physical activity, and the interaction between genotype and physical activity. Analysis revealed that on the more difficult conditions of the memory task as physical activity level increased, reaction time significantly decreased for APOE e4 carriers. No such relationship existed for noncarriers. These results imply, compared with other cognitive challenges, physical activity serves a protective role for maintaining memory, particularly in those who are at a genetic risk for developing dementia.
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    The Dynamics of Multi-sensory Re-weighting in Healthy and Fall-prone Older Adults
    (2006-08-04) Allison, Leslie K.; Jeka, John J.; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Multi-sensory re-weighting (MSR) is an adaptive process that prioritizes the visual, vestibular and somatosensory inputs that provide the most reliable information when environmental conditions change. This process is thought to degrade with increasing age, and to be particularly deficient in fall-prone versus healthy older adults. This dissertation presents three studies designed to investigate age- and fall-related changes in MSR. The first study examined the assumption of impaired MSR in healthy and fall-prone older adults using a two-frequency touch/vision experimental design with stimuli at varying amplitudes. Both healthy and fall-prone older adults demonstrated the same pattern of adaptive gain changes as healthy young adults. No group differences in the overall levels of vision and touch gain were found. These results suggest that, for small amplitude vision and touch stimuli, the central sensory re-weighting adaptation process remains intact in healthy and fall-prone older adults. In the second study the effects of a sensory-challenge balance exercise program on laboratory measures of MSR and clinical measures of balance were investigated. Following the intervention the normal adaptive pattern of gain change was unaltered, while declines in overall vision and touch gains that reflect down-weighting of the sensory stimuli were seen. Improvements in four clinical balance measures were observed. These findings indicate that MSR processes in fall-prone older adults are modifiable, that sensory challenge balance exercises may facilitate the ability to down-weight unstable sensory inputs, and that these effects may generalize to other components of balance. A third study explored the dynamics of sensory re-weighting in healthy and fall-prone older adults. Absolute levels of gain, and the rate of adaptive gain change, were examined before and after large changes in visual motion stimulus amplitude. Compared to young adults, gains in both older adult groups were higher when the stimulus amplitude was high, and gains in the fall-prone elderly were higher than both other groups when the stimulus amplitude was low. Both older groups demonstrated slowed sensory re-weighting over prolonged time periods when the stimulus amplitude was high. These results reflect age- and fall-related changes in the extent and rate of down-weighting unstable visual inputs.
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    Postural Coordination Patterns: Visual Rotation and Translation
    (2006-04-19) Zhang, Yuanfen; Jeka, John; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Recent studies have shown co-existing trunk-leg coordination patterns during quiet stance: in-phase and anti-phase for frequencies below and above 1 Hz, respectively. Two experiments investigated whether the nervous system assumes a multilinked internal model in sensory coupling? In the first experiment, we investigated the influence of the addition or removal of sensory information on these patterns. Trunk-leg coherence decreased with the addition of static vision and light touch, in the AP and ML directions, respectively, at frequencies below 1 Hz, suggesting the in-phase pattern may be more affected by neural control than the anti-phase pattern. In the second experiment, we compared translation of the visual field to a rotation relative to the ankle/hip. Gain and phase between the trunk/leg angles relative to the visual display showed only minor condition differences. The overall results suggest the nervous system adopts a simple control strategy of a single-link internal model at low frequencies.
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    EXERCISE BEHAVIOR AND MAINTENANCE OF CEREBRAL CORTICAL ACTIVITY DURING COGNITIVE CHALLENGE IN MIDDLE-AGED MEN AND WOMEN GENETICALLY AT RISK FOR DEMENTIA: A MEGNETOENCEPHALOGRAPHIC STUDY
    (2005-04-20) Deeny, Sean Patrick; Hatfield, Brad D; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Exercise is known to protect and enhance cognitive function in normal aging through increased blood flow and upregulation of neurotrophic factors in the brain. One recent study suggests that carriers of a known genetic risk factor for Alzheimer's disease (AD), the apolipoprotein E (APOE) E4 allele, may exhibit a more profound benefit of exercise on neurocognitive function relative to non-E4 carriers. Brain imaging studies in cognitively normal, middle-aged E4 carriers have revealed deficits in temporal and parietal cortical function even in the absence of clinical symptoms of dementia. As exercise has been shown to protect these regions in normal aging, and even enhance cortical functioning, the current study employs magnetoencephalographic (MEG) measures of cortical activation during the Ericksen flanker task and the Sternberg working memory task to examine whether highly physically active 50-70 year old E4 carriers and non-carriers, who are free from dementia, exhibit greater cortical activation in task-related regions relative to their low-active counterparts. The results revealed that high-active participants, regardless of genotype, exhibited greater activation on the Ericksen flanker task in the right frontal and right temporal regions relative to low-active participants, while performing similarly on accuracy and reaction time (RT). On the Sternberg working memory task high-active E4 carriers exhibited greater activation than low-active E4 carriers in the right temporal region, while being undifferentiated from both the high-active and low-active non-E4 carriers. This effect was most pronounced in the 150-200 ms post-stimulus time window. All groups performed similarly on accuracy and RT. The results suggest that high-resolution brain imaging methods are sensitive to differences in brain function in populations at different genetic risk for dementia prior to any signs of clinical impairment. Furthermore, the relationships between physical activity and brain function are measurable and distinguishable between groups of different genetic susceptibility on tasks and brain regions specific to AD-related neurocognitive decline. The findings support the notion that populations genetically at risk for dementia who remain sedentary may be at greater risk for decline in brain function relative to those who are physically active.