Cognitive and motor impairments have been identified as signs following a concussion which may compromise the performance of everyday tasks or physical activities. However, little work has been done in the adolescent population using laboratory based measurements of attention or balance control to identify recovery from concussion. Therefore, the purpose of this dissertation was to prospectively and longitudinally observe how individuals who have sustained a concussion recover on measures of attention and gait balance control in comparison to individually matched, healthy control subjects from within 72 hours of injury up to two months following injury. Individuals were identified as sustaining a concussion by healthcare professionals and began participation in the study within 72 hours of injury. They then returned to the laboratory at approximately 1 week, 2 weeks, 1 month, and 2 months post-injury. Control subjects were individually matched by sex, age, height, and weight and tested in similar time increments. Attentional abilities were measured via multiple computerized testing assessments, and gait balance control was measured with whole-body motion analysis. The results indicated that following concussion, adolescents display deficits in conflict resolution ability, task switching ability, and gait balance control during dual-task walking for a time period of up to two months following injury in comparison to a matched control group. During dual-task walking, the complexity of the cognitive task performed may affect adolescents with concussion to a greater degree than matched control subjects. Adolescents also displayed regressions to gait stability recovery following their return to physical activities. Finally, adolescents with concussion displayed greater gait balance control deficits than young adults with concussion throughout the two months of testing when each group was compared to a respective healthy control group. Results from this dissertation indicate that concussion affects cognitive and motor functions in adolescents, who display deficits throughout two months post-injury. Computerized attentional tests and dual-task dynamic balance control assessments represent a multifaceted approach to concussion management and may provide another assessment battery for healthcare professionals to utilize in order to identify recovery following concussion. This dissertation includes previously published/unpublished co-authored material.

The purpose of the present thesis was two-fold. First, to evaluate the impact of cognitive demand on postural control in young adults and second, to examine the responsiveness of postural control to cognitive tasks presented in varying modalities. Seventeen young adults stood on a force platform while simultaneously performing cognitive tasks of varying difficulty (easy, moderate and difficult), each presented auditorily and visually. Performing the moderate and difficult tasks precipitated a greater reduction in area of 95% confidence ellipse and medio-lateral (ML) sway variability compared to the easy tasks. Presenting the tasks visually produced lower ML sway variability than presenting the tasks auditorily. Of secondary interest of this thesis was to determine if the duration of inter-stimulus intervals could modify the effectiveness of a cognitive task on postural control. Participants stood on a force platform while simultaneously performing cognitive tasks with five-second inter-stimulus intervals (i.e. discrete) and two-second inter-stimulus intervals (i.e. continuous), each presented auditorily and visually. Results revealed higher anterior-posterior (AP) mean power frequency (MPF) when performing the continuous tasks. In addition, presented the tasks visually resulted in a greater reduction in area of 95% confidence ellipse, AP and ML sway variability.

Visually focusing on the hole versus the ball in golf has shown some positive effects on putting performance (Heath et al., 2008), yet the reason for these benefits have not been tested. Considering the benefits of adopting an external focus, the purpose here was to examine whether attentional focus mechanisms contribute to the positive effects reported by Heath et al. (2008). Thirty experienced golfers were assigned to either a visual-ball focus or visual-hole focus group. Following warm-up putts, 48 experimental putts, divided equally into 16 putts across three conditions: control, task-relevant, and task-irrelevant, were performed. In the control condition, participants putted under single-task conditions, maintaining their assigned visual focus. In the other two conditions, participants putted under dual-task conditions and were instructed to focus on their wrist angles upon hearing a tone (task-relevant), or to identify an irrelevant sound (task-irrelevant). A questionnaire, designed to represent equal proportions of the ‘distance’ effect (Wulf, 2013; i.e., internal, proximal external, or distal external focus), served as a manipulation check to determine the attentional focus adopted under each condition. Analysis of the manipulation check for the control condition data only showed a significant interaction of Group and Attentional Focus F(2,56) = 4.5, p = .01. Post-hoc showed that participants had a significantly higher proximal external focus in the visual-ball focus group compared to the visual-hole focus group, whereas the visual-hole focus group was significantly higher than the visual-ball focus group for distal external focus. Additionally, an analysis with all three putting conditions indicated that participants had significantly higher internal focus for task-relevant trials, as compared to task-irrelevant or control trials. There were no significant differences found for any of the putting performance measures., however, the main effect of Condition did approach significance for MRE F(2,56) = 2.8, p = .068. This replicates the general finding that putting performance is poorest when golfers self-report using a higher internal focus. In conclusion, these results suggest that visually focusing on the hole results in a more distal external attentional focus in a golf environment than that of a ball-focus, but this does not translate to performance benefits.

The objective of the present study was to; 1) determine if the use of a continuous cognitive task demonstrates distinct characteristics of a more automatic control of posture, compared to an external focus (EF) and feet together (FT) postural task, and to 2) examine which condition, if any, exhibits the characteristics of increased ankle stiffness proposed by Winter et al. (1998), as well as displaying increased ankle muscular co-contractions, which are a suggested neuromuscular mechanism that stiffens posture. Fifteen young adults stood on a force platform and performed 4 separate conditions: FT, EF, single number sequence (SNS), and double number sequence (DNS). Throughout the session, surface electromyography (EMG) signals were collected from the tibialis anterior (TA) and medial gastrocnemius (MG) of each leg. Each testing session consisted of 24 trials, with 6 per condition. Results displayed decreased sway area for SNS and DNS compared to FT. Sway variability in the anterior/posterior (AP) direction SNS and DNS were smaller compared to EF and FT. As well sway variability in the medial/lateral (ML) direction was smaller for SNS and DNS compared to FT. ML Mean velocity (MV) did not differ across conditions, though in the AP direction it was larger for SNS and DNS compared to EF and FT. AP Mean power frequency (MPF) was larger for SNS compared to FT. In the ML direction MPF was larger for SNS and DNS compared to FT. Co-Contraction indices revealed no differences across conditions. Conversely the left TA for DNS revealed increased EMG activation compared to EF and SNS.

INTRODUCTION: Age-related functional declines in the body and brain pose significant challenges to mobility and postural control. Older individuals are at increased risk for injury from a fall. Declines in gait and balance control make older adults more likely to suffer a fall or recurrent falls. According to the Centers for Disease Control and Prevention (CDC), falls are the leading cause of injury related death among adults age 65 years and older. (Important Facts about Falls | Home and Recreational Safety | CDC Injury Center, 2019) One out of three older adults falls annually and the likelihood of falling increases with age. (Stevens et al., 2008). In the US alone, the number of individuals living aged 65 and older is estimated at 46 million persons and is expected to reach 74 million by 2030. (Healthy Aging in Action: Advancing the National Prevention Strategy, 2019) Fall death rates in the United States increased by 30% from 2007 to 2016, and if this trend continues, it is expected that by 2030 there will be 7 deaths due to falls every hour. (Important Facts about Falls | Home and Recreational Safety | CDC Injury Center, 2019) Interventions designed to improve gait and balance control in the geriatric population can mitigate fall risk and positively impact these trends. OBJECTIVE: Gait and balance control, traditionally regarded as automatic motor processes, have since been determined to be complex motor functions reliant on executive function. (Hausdorff et al., 2005; Woollacott & Shumway-Cook, 2002) Normal walking and balance control are attentionally demanding and require shifting of attentional resources to frontal brain regions in order to maintain upright stance. This ability to dual-task is impaired in older adults. A single session of transcranial direct current stimulation (tDCS), a form of noninvasive brain stimulation, targeting the excitability of the left dorsolateral prefrontal cortex (l-dlPFC) has been found to reduce dual-task costs to gait and balance in both young and healthy older adults. (Manor et al., 2016; Zhou et al., 2014) However, little is known about how tDCS influences electroencephalogram (EEG) patterns and if changes in EEG are associated with functional outcomes. The specific aims of this study were to determine whether 1, 20-minute session tDCS targeting the l-dlPFC reduces the slow-wave/fast-wave frequency power ratio in EEG and absolute EEG power and whether these reductions are associated with changes in measures of postural control. METHODS: The data from this study was analyzed as part of a larger clinical trial testing multiple tDCS stimulation montages in combination with batteries of cognitive, gait, and balance assessments. Twenty-two older adults (median age=71 years) who were free of overt illness or disease were included in the analysis. Participants were outfitted with wireless movement sensors and a wireless 32-electrode EEG cap configured according to the 10-20 system. Participants completed a dual-task of serial subtraction by 3’s from a randomized three-digit number while standing for 60 seconds. EEG was simultaneously recorded during the 60 second trials. One, 20-minute tDCS stimulation targeting the l-dlPFC followed the balance assessment. EEG and dual-task assessments were repeated following the stimulation. EEG was not recorded simultaneously with tDCS. EEG data was processed and analyzed with Cartool EEG software. (Brunet et al., 2011) Spectral analysis of the EEG power values pre and post stimulation was conducted using a paired t-test. Power ratios of slow wave (4-8Hz) to fast wave (12-30Hz) were calculated for pre and post stimulation and analyzed for significant changes. Additionally, absolute power values in theta and beta frequency range were calculated. Postural sway velocity and postural sway area were also assessed and analyzed for changes following stimulation. RESULTS: Spectral analysis showed significant reductions in absolute power values across low theta frequency ranges following stimulation. This significant reduction in power was localized, but not exclusive, to frontal electrodes measuring activity of the l-dlPFC in the 4-8Hz frequency range. Most notably electrode F3, which has been found to correspond to the location and activity of the l-dlPFC using both the 10-20 electrode placement system and MRI guided neuronavigation. (Beam et al., 2009; De Witte et al., 2018) In addition to a significant reduction in power values, there was a reduction in slow-fast EEG ratios following stimulation. The percent reduction in EEG ratio was associated with a reduction in postural sway area (m2/s4) and sway velocity (m/s). CONCLUSION: tDCS is used to facilitate the excitability of cortical neurons. The l-dLPFC is a critical component of executive function. Due to the role of executive function in mediating attentional requirements of gait and balance, the l-dlPFC was chosen as a target to enhance dual-tasking capabilities, and thereby improve gait and postural control. The reduction in the slow wave-fast wave ratio and theta power indicates that participants had higher power in the fast wave relative to the slow wave after tDCS administration. The reduction in slow wave power may be indicative of less cognitive attentional effort required to complete a simultaneous dual-task involving postural control. This is supported by the associated reductions in postural sway following tDCS stimulation. These results further current research of tDCS as a viable intervention for improving balance and cognition in older adults and offers additional information about optimizing the efficacy of noninvasive brain stimulation to improve functional outcomes in this population.

京都大学 / 0048 / 新制・課程博士 / 博士(人間健康科学) / 甲第19179号 / 人健博第27号 / 新制||人健||3(附属図書館) / 32171 / 京都大学大学院医学研究科人間健康科学系専攻 / (主査)教授 三谷 章, 教授 村井 俊哉, 教授 精山 明敏 / 学位規則第4条第1項該当 / Doctor of Human Health Sciences / Kyoto University / DFAM

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This study investigated the impacts of dual task and time pressure conditions on the speech fluency of 60 neurotypical adults between the ages of 26 and 85. Participants retold short stories in baseline, time pressure, dual task, and combined dual task and time pressure conditions. Dependent variables included five measures of speech fluency: words per minute (WPM), fillers per verbalization, false starts and repetitions per verbalization, extended pauses per utterance, and speech naturalness. Each of these variables was compared between age groups of younger, older, and elderly adults and across conditions. Results reveal that time pressure causes speech rate to increase across age groups but combining time pressure with a dual task condition mitigates this effect in elderly speakers. Additionally, younger adults are perceived to have more natural speech compared to older and elderly adults. Speakers across age groups perform similarly in all other variables of speech fluency, with notable changes in fluency under the combined dual task and time pressure condition compared to other conditions. These findings suggest that while speakers do not always become less fluent as attentional demands increase, the combination of dual task and time pressure conditions can cause attentional demands to surpass capacity and/or resource allocation thresholds for fluent speakers. Future research should continue investigating the effect of time pressure and other divided attention conditions on typical speakers and those with communication disorders to establish methods for optimizing conditions for effective communication in everyday situations.

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Yes / Background: Past research has found cancellation tasks to be reliable markers of cognitive decline in Huntington’s disease (HD). Objective: The aim of this study was to extend previous findings by adopting the use of a dual task paradigm that paired cancellation and auditory tasks. Methods: We compared performance in 14 early stage HD participants and 14 healthy controls. HD participants were further divided into groups with and without cognitive impairment. Results: Results suggested that HD participants were not slower or less accurate compared with controls; however, HD participants showed greater dual task interference in terms of speed. In addition, HD participants with cognitive impairment were slower and less accurate than HD participants with no cognitive impairment, and showed greater dual task interference in terms of speed and accuracy. Conclusions: Our findings suggest that dual task measures may be a better measure of cognitive processing in HD compared with more traditional measures. / Supported by the School of Psychological Sciences, Monash University.