The effect of cognitive resource competition due to dual-tasking on the irregularity and control of postural movement components

Postural control research suggests a non-linear, n-shaped relationship between dual-tasking and postural stability. Nevertheless, the extent of this relationship remains unclear. Since kinematic principal component analysis has offered novel approaches to study the control of movement components (PM) and n-shapes have been found in measures of sway irregularity, we hypothesized (H1) that the irregularity of PMs and their respective control, and the control tightness will display the n-shape. Furthermore, according to the minimal intervention principle (H2) different PMs should be affected differently. Finally, (H3) we expected stronger dual-tasking effects in the older population, due to limited cognitive resources. We measured the kinematics of forty-one healthy volunteers (23 aged 26 +/- 3; 18 aged 59 +/- 4) performing 80 s tandem stances in five conditions (single-task and auditory n-back task; n = 1-4), and computed sample entropies on PM time-series and two novel measures of control tightness. In the PM most critical for stability, the control tightness decreased steadily, and in contrast to H3, decreased further for the younger group. Nevertheless, we found n-shapes in most variables with differing magnitudes, supporting H1 and H2. These results suggest that the control tightness might deteriorate steadily with increased cognitive load in critical movements despite the otherwise eminent n-shaped relationship.(VLID)3676012Version of recor

Watch your head: brain neurophysiology and contact sports

In the world of contact sports there is rising concern about the long-term effects of sport participation on athletes’ brains. Apart from concussions, the repetitive subconcussive head impacts (RSHI) in sports have been suggested to be detrimental for brain health. RSHI in football are thought to be linked with the onset of neurodegenerative diseases, like Chronic Traumatic Encephalopathy and Alzheimer’s disease. However, to understand how and why the athletes’ brains might suffer in the long-term, we should first understand the acute brain changes caused by the potential risk factors for brain damage (concussive and sub-concussive impacts). The experimental studies of this PhD thesis aim to investigate the acute effects of heading, the main source of RSHI in football, on the brain functions of athletes, by using a mixture of sensitive neuroscientific modalities. Secondary data is used in this thesis for method development and to examine the broader problem posed by sport-related head impact. Chapter 1 expands on the aims of the thesis. Chapter 2 presents the current state of the literature on RSHI. Chapter 3 includes a scoping review of the literature on biofluid markers use to assess the effects of RSHI highlighting the high heterogeneity of the existing studies and providing guidelines for future studies. Chapter 4 includes an investigation of the injury characteristics and prognosis of sport-related traumatic brain injury (TBI). It highlights the seriousness of sport-related TBI and specifically sport-related mTBI, whose remaining effects can potentially be worsened by the burden of RSHI during play. Chapter 5 investigated the effects of RSHI on balance in various ways, providing no evidence of an effect, while chapter 6 provides evidence for associative memory changes caused by heading. The following chapters (7 & 8) attempted to further examine the alterations in cognitive functioning post heading and present the first EEG evidence that the cognitive functions of attention, memory and learning are acutely affected by RSHI. After showing that RSHI affect mainly association learning and attention processes and not affect response inhibition, motor control and motor learning, chapter 9 aimed to examine the replicability of RSHI effects on motor cortex inhibition, providing evidence of no effect. The outcome of this thesis is that RSHI have detrimental effects to athletes’ cognition, mainly in the functions of learning and attention, while motor control appears to remain intact