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Mental Workload Assessment During Upper Limb Prosthetic Training and Task Performance
(2023) Gaskins, Peter Christopher; Gentili, Rodolphe J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Mental workload, defined as the recruitment and allocation of cortical resources in response to task demands, is an integral underlying mechanism of cognitive-motor learning and performance. Although widely examined in individuals without motor impairment, the study of mental workload in a clinical context of motor rehabilitation is limited. In particular, it is not well understood how the cortical processes underlying mental workload adapt over time as individuals learn to operate upper-limb prosthetic devices. In this work, mental workload assessment using electroencephalography (EEG) along with other ancillary measurement tools were employed to examine the recruitment of cognitive-motor processes as individuals learned to operate either a body-powered (BP) or myoelectric (MYO) bypass prosthesis during a ten session upper limb prosthetic training program. The first two studies examined changes in mental workload and cognitive-motor performance as prosthesis users executed tasks requiring transport of objects with the same or different shape/size during a prosthetic training program. Then, these newly trained prosthesis users engaged in activities which manipulated contextual demands to examine how real-world scenarios affect mental workload and cognitive-motor performance. Finally, a preliminary validation of a novel mental workload self-report measure aimed to address the paucity of mental workload measurement tools in upper-limb rehabilitation was implemented. Although these four studies offer a rich and complex pattern of results, the main findings suggested that i) while both prosthetic groups experienced similar levels of cognitive-motor performance by the end of training, the BP group exhibited more refined cortical dynamics and better cognitive-motor efficiency when compared to the MYO group, thus indicating a more advanced progression of learning; ii) contextual demands degrade mental workload and cognitive-motor performance similarly in both prosthetic groups and; iv) the preliminary assessment of reliability and validity of the novel mental workload self-report measure shows promise for capturing changes in mental workload during cognitive-motor performance in a rehabilitation context. Although more research is warranted to confirm and extend the findings of this work to clinical upper-limb prosthesis users, this work has the potential to inform the cognitive-motor processes in this population and inform prescriptive decisions for patient device selection, prosthetic device design and rehabilitation program development.
ACUTE EXERCISE INDUCED MICROSTRUCTURAL AND FUNCTIONAL CHANGES IN THE HIPPOCAMPUS OF OLDER ADULTS
(2023) Callow, Daniel; Carson, Jerome J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Declining memory function is a common complaint of aging adults and a primary symptom of mild cognitive impairment (MCI) and Alzheimer’s disease (AD). The hippocampus is often the first brain area to exhibit noticeable deficits in age and pathologically-related cognitive decline and is a necessary structure for proper memory function. More specifically, the dentate gyrus (DG) and the third cornu ammonis area (CA3) of the hippocampus directly support mnemonic discrimination (MD), which is the process of reducing interference among new representations and distinctly encoding them as independent memories. Poor MD is associated with age and is a presymptomatic biomarker of cognitive decline and is believed to result from reduced neurogenesis, angiogenesis, and synaptogenesis within the DG/CA3 subregion of the hippocampus. While causes and treatments for memory decline remain elusive, lifestyle interventions, especially physical activity, have received attention as cost-effective and safe means of ameliorating and potentially preventing cognitive decline in a growing aging population. Animal and human studies suggest exercise benefits the hippocampal structure, preserving neurogenesis and angiogenesis in aging rodents and macrostructure and memory in older adults. However, the mechanisms by which exercise affects the human hippocampus remains a significant knowledge gap in the field and is a critical aspect in understanding the long-term impact exercise has on the aging hippocampus. To better address this gap, researchers have begun implementing acute exercise studies, which allow for greater control of non-exercise-related factors, are cheaper and more time efficient to conduct than training studies, and can predict and inform training-related adaptations. Unfortunately, limitations in the study designs, population tested, specificity of cognitive tasks, and spatial resolution of human imaging techniques have posed significant barriers to our understanding of how acute exercise relates to healthy brain aging at the functional and microstructural levels. Therefore, the objective of this dissertation was to expand our understanding of how acute aerobic exercise alters the function and microstructure of the aging hippocampus. Three within-subject studies were conducted comparing the relationship between a 30-minute bout of moderate to vigorous intensity aerobic exercise vs seated rest on MD performance, hippocampal microstructure, and high-resolution hippocampal-subfield microstructure and functional activity in healthy older adults. In study one, acute exercise preserved MD performance compared to decrements exhibited after seated rest in a pre and post-condition study design. In study two, a post-condition-only study design, acute exercise elevated microstructural diffusion within the hippocampus, indicative of a hippocampal neuroinflammatory response and upregulation of neurotrophic factors. Finally, in study three, a post-condition-only study design, we found that acute exercise resulted in lower MD, suppressed MD-related DG/CA3 network hyperactivity (indicative of healthier network function), and led to higher DG/CA3 extracellular diffusion. However, these neuroimaging-based correlates of hippocampal neuroplasticity and network function were not associated with differences in MD performance. These findings suggest that higher-intensity acute exercise can alter memory performance and stimulate neuroplasticity and neurotrophic cascades within the hippocampus and the DG/CA3 subfield, potentially via different mechanisms. Furthermore these results give insight into the immediate neurotrophic and behavioral effects of acute moderate to vigorous intensity aerobic exercise in older adults and provide new methods and tools for better understanding if and how exercise promotes healthy brain aging. Finally, these initial findings lay a foundation for optimizing exercise prescription and identifying future effective exercise treatments.
NEURAL FEEDBACK CONTRIBUTION TO HUMAN LOCOMOTION CONTROL
(2020) Rafiee, Shakiba; Miller, Ross H.; Kiemel, Tim; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
The human nervous system stabilizes locomotion by continuously correcting for deviations away from the desired gait pattern through making transient changes to muscle excitations. We refer to this correction process as “muscle modulation”. It remains unknown how muscle modulations are implemented in the larger framework of human neuromuscular control to achieve stability. Such knowledge has implications across various health and engineering fields. Systematic identification of the properties of the nervous system can provide insight into the role that different muscle modulations play in human walking. Additionally, mathematical models of human walking can be used to test the validity of different neural controllers. In this thesis, we devised three studies to further our understanding of the role different muscle modulations play in human walking and hypothesize the neural mechanisms involved in producing them. In study one, we investigated the role of the ankle dorsiflexor muscle, tibialis anterior, modulation in the control and stability of human walking. Previous research from our lab has suggested a novel role for the tibialis anterior in speed control during early stance. To investigate this role, we imposed a restriction on ankle dorsiflexion using a taping method, which limited the ability of this muscle to accelerate the body forward during early stance. We characterized the kinematic and muscular responses of this “restricted” walking to mechanical perturbations and compared the results with those from “normal” human walking. Our results support the idea that early stance modulation of tibialis anterior muscle regulates speed control. In studies two and three, we used mathematical models of human walking to investigate the neural mechanisms involved in foot-placement. In study two, we examined whether a model of human locomotion that is purely controlled by spinal reflex mechanisms can produce muscle modulations observed in human locomotion. In study three, we developed a model of human walking and examined its response to mechanical perturbations of the leg. Together these studies provided insight into the types of neural mechanisms the human nervous system uses to stabilize walking. We observed that gated reflex mechanisms can produce some of the human responses to external perturbations, but not all.
STRUCTURAL AND FUNCTIONAL BRAIN NETWORK CORRELATES OF PHYSICAL ACTIVITY AND CARDIORESPIRATORY FITNESS: EXAMINING THE INFLUENCE OF DEPRESSION
(2020) Weiss, Lauren; Smith, J. Carson; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Physical activity (PA) and improvements in cardiorespiratory fitness (CRF) may protect against or alleviate depression through neuroplastic mechanisms within disrupted brain networks underlying cognitive and affective symptoms. There is a scarcity of research examining the effects of PA and CRF on structural and functional brain networks in representative samples spanning adulthood. Further, little is known about the interactions of PA and CRF with depression on these networks. To address this problem, this dissertation made use of a publicly available dataset to examine the associations among PA, CRF, and depression symptoms in a community sample of adults between the ages of 18-85. Magnetic resonance imaging measures were leveraged to determine whether structural and functional brain network features associated with PA and CRF were moderated by depression symptom severity. The first aim examined effects of PA and CRF on depression symptoms within a measured variable path analysis. PA had a direct and beneficial effect on depression symptoms only in females, and this effect was not mediated by CRF. The second aim examined brain structural correlates of PA and CRF and tested moderation of these effects by depression symptoms. CRF was negatively associated with cortical thickness in the left superior frontal lobe, and this association was stronger as depression symptoms increased. CRF was negatively associated with amygdala and nucleus accumbens volume, while a positive association of PA with nucleus accumbens volume was observed at moderate-to-severe levels of depression symptoms. The third aim examined functional brain network correlates of PA and CRF and moderation by depression symptoms. CRF was positively associated with whole-brain modularity, between-network connectivity of the central executive and salience networks, and within-network connectivity of the default mode, central executive, and salience networks. The association of CRF and default mode network connectivity was stronger in the presence of moderate-to-severe depression symptoms. Taken together, these results suggest psychosocial effects of PA on depression symptoms and interacting effects of CRF and depression on brain structure and function. Progressing our understanding of these effects will have important implications for translating physical activity and exercise research as a therapeutic strategy for depression symptoms.
Effect of spatial working memory depletion on cerebral cortical dynamics of cognitive-motor performance
(2020) Shaw, Emma Patricia; Gentili, Rodolphe J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Prior work has validated the use of resource depletion to directly probe the role of specific cognitive functions on human performance. Specifically, intensive recruitment of cognitive resources to successfully perform a task has been shown to result in performance decrements and decreased neural activation on subsequent tasks. Much of this work, however, was not conducted within the context of cognitive-motor performance and/or did not examine the underlying brain dynamics. Therefore, this study examined the effects of depleted spatial working memory (SWM) resources, critical for spatial information processing, on performance and brain dynamics (attentional reserve and cognitive-motor effort). Performance and electroencephalography were collected as thirty-five individuals, randomly assigned to an experimental or control group, with minimal prior videogame experience completed a cognitive-motor task at an easy and a hard level of difficulty before and after undergoing SWM resource depletion (experimental) or non-depletion (control). The SWM depletion protocol required intensive mental rotation, while the non-depletion protocol did not. Attentional reserve was assessed via the novelty-P3 component of the event-related potential and cognitive-motor effort was assessed via spectral power within the theta, low- and high-alpha frequency bandwidths. The results revealed both groups exhibited similar performance improvement on the cognitive-motor task post- compared to pre-SWM depletion/non-depletion. This was accompanied with a more efficient engagement of attentional resources (decreased novelty-P3) and a refinement of cortical activity (low-/high-alpha synchrony), which may reflect a practice effect. Furthermore, the control group exhibited theta synchrony under the hard compared to the easy level of challenge across all cortical regions regardless of when the cognitive-motor task was performed. This adaptive response, however, was absent within the frontal and temporal cortical regions (important for working memory, attentional control and visuospatial processes) for the experimental group post-SWM depletion. Additionally, the experimental group, post-relative to pre-SWM depletion, exhibited temporal theta desynchrony and synchrony during the hard and easy level of challenge, respectively. These findings collectively suggest intensive cognitive task performance has a combined neurocognitive benefit (i.e., practice effect) and cost (i.e., lack of adaptive response due to depleted resources) during subsequent cognitive-motor performance requiring similar cognitive processes as that of the depleting task.
THE INFLUENCE OF MOTIVATION ON EMOTION REGULATION AND MOTOR PERFORMANCE: EXAMINATION OF A NEURO-AFFECTIVE MODEL
(2016) Tan, Ying; Hatfield, Bradley D; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Mental stress is known to disrupt the execution of motor performance and can lead to decrements in the quality of performance, however, individuals have shown significant differences regarding how fast and well they can perform a skilled task according to how well they can manage stress and emotion. The purpose of this study was to advance our understanding of how the brain modulates emotional reactivity under different motivational states to achieve differential performance in a target shooting task that requires precision visuomotor coordination. In order to study the interactions in emotion regulatory brain areas (i.e. the ventral striatum, amygdala, prefrontal cortex) and the autonomic nervous system, reward and punishment interventions were employed and the resulting behavioral and physiological responses contrasted to observe the changes in shooting performance (i.e. shooting accuracy and stability of aim) and neuro-cognitive processes (i.e. cognitive load and reserve) during the shooting task. Thirty-five participants, aged 18 to 38 years, from the Reserve Officers’ Training Corp (ROTC) at the University of Maryland were recruited to take 30 shots at a bullseye target in three different experimental conditions. In the reward condition, $1 was added to their total balance for every 10-point shot. In the punishment condition, $1 was deducted from their total balance if they did not hit the 10-point area. In the neutral condition, no money was added or deducted from their total balance. When in the reward condition, which was reportedly most enjoyable and least stressful of the conditions, heart rate variability was found to be positively related to shooting scores, inversely related to variability in shooting performance and positively related to alpha power (i.e. less activation) in the left temporal region. In the punishment (and most stressful) condition, an increase in sympathetic response (i.e. increased LF/HF ratio) was positively related to jerking movements as well as variability of placement (on the target) in the shots taken. This, coupled with error monitoring activity in the anterior cingulate cortex, suggests evaluation of self-efficacy might be driving arousal regulation, thus affecting shooting performance. Better performers showed variable, increasing high-alpha power in the temporal region during the aiming period towards taking the shot which could indicate an adaptive strategy of engagement. They also showed lower coherence during hit shots than missed shots which was coupled with reduced jerking movements and better precision and accuracy. Frontal asymmetry measures revealed possible influence of the prefrontal lobe in driving this effect in reward and neutral conditions. The possible interactions, reasons behind these findings and implications are discussed.
The Impact of Motor Learning on Motor Behavior and Cortical Dynamics in a Complex Stressful Social Environment
(2016) Saffer, Mark Ian; Hatfield, Bradley; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
An economy of effort is a core characteristic of highly skilled motor performance often described as being effortless or automatic. Electroencephalographic (EEG) evaluation of cortical activity in elite performers has consistently revealed a reduction in extraneous associative cortical activity and an enhancement of task-relevant cortical processes. However, this has only been demonstrated under what are essentially practice-like conditions. Recently it has been shown that cerebral cortical activity becomes less efficient when performance occurs in a stressful, complex social environment. This dissertation examines the impact of motor skill training or practice on the EEG cortical dynamics that underlie performance in a stressful, complex social environment. Sixteen ROTC cadets participated in head-to-head pistol shooting competitions before and after completing nine sessions of skill training over three weeks. Spectral power increased in the theta frequency band and decreased in the low alpha frequency band after skill training. EEG Coherence increased in the left frontal region and decreased in the left temporal region after the practice intervention. These suggest a refinement of cerebral cortical dynamics with a reduction of task extraneous processing in the left frontal region and an enhancement of task related processing in the left temporal region consistent with the skill level reached by participants. Partitioning performance into ‘best’ and ‘worst’ based on shot score revealed that deliberate practice appears to optimize cerebral cortical activity of ‘best’ performances which are accompanied by a reduction in task-specific processes reflected by increased high-alpha power, while ‘worst’ performances are characterized by an inappropriate reduction in task-specific processing resulting in a loss of focus reflected by higher high-alpha power after training when compared to ‘best’ performances. Together, these studies demonstrate the power of experience afforded by practice, as a controllable factor, to promote resilience of cerebral cortical efficiency in complex environments.
Influence of Acute and Chronic Exercise on Markers of Hippocampal Plasticity
(2016) Venezia, Andrew Carmen; Roth, Stephen M; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Exercise and physical activity are lifestyle behaviors associated with enriched mental health. Understanding the mechanisms by which exercise and physical activity improve mental health may provide insight for novel therapeutic approaches for numerous mental health disorders. This dissertation reports the findings from three studies investigating the influence of acute and chronic exercise on behavioral and mechanistic markers of hippocampal plasticity and delves into the potential role of noradrenergic signaling in the hippocampal adaptations with exercise. The first study assessed the effects of long-term voluntary wheel running on hippocampal expression of plasticity-associated genes and proteins in adult male and female C57BL/6J mice, highlighting sex differences in the adaptations to long-term voluntary wheel running. The second study examined the influence of acute exercise intensity on AMPA receptor phosphorylation, a mechanism essential for hippocampal plasticity, plasticity- associated gene expression, spatial learning and memory, and anxiety-like behavior. The unexpected finding that acute exercise increased anxiety-like behavior encouraged investigation into the role of central noradrenergic signaling in acute exercise-induced anxiety. The third study determined how previous exposure to voluntary wheel running modulates the response to an acute bout of exercise, focusing primarily on transcription of the important plasticity-promoting gene, brain-derived neurotrophic factor. Using a pharmacological approach to compromise the locus coeruleus noradrenergic system, a system that is implicated in age-related mental health disorders such as Alzheimer’s Disease, the third study also investigated the influence and interaction of the noradrenergic system and acute exercise on expression of multiple brain-derived neurotrophic factor transcripts. Together, this dissertation reports the findings from a series of experiments that explored similarities, differences, and interactions between the effects of acute and chronic exercise on markers of hippocampal plasticity and behavior. Further, this work provides insight into the role of the noradrenergic system in exercise-induced hippocampal plasticity.
The effects of sequence structure, age-related impairments, and Parkinson's disease on motor sequence learning
(2015) Prashad, Shikha; Clark, Jane E.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Parkinson’s disease (PD) is a neurodegenerative movement disorder that affects over one million individuals in the US with approximately 60,000 new diagnoses every year. While characterized as a movement disorder, the effect of PD and aging on learning new motor skills has yielded equivocal results. Thus, the broad objective of this dissertation is to investigate the influence of PD on motor sequence learning. We begin by examining different sequence structures and how they are affected by age before investigating the effects of PD. To address the inadequacies of previous studies using fixed order sequences, we used probabilistic sequences, in which stimuli are linked by statistical associations. The first study directly compared the learning of probabilistic sequences to fixed sequences and randomly ordered stimuli in typical young adults (18-23 years) using a modified serial reaction time (SRT) paradigm. The results suggest that both fixed and probabilistic sequence groups exhibited learning, but the underlying learning processes were different in employing online and offline learning strategies. In the second and third studies, electroencephalography (EEG) was recorded from typical young adults (18-23 years), typically aging adults (55-75 years), and patients with PD (55-75 years) while they performed the same modified SRT task. We characterized the developmental landscape of 55-75 year old adults and found that cluster analysis separated typically aging adults into groups that provided a clearer understanding of their impairments. By unraveling movement and cognitive deficits and matching participants based on functional characteristics, we found that some typically aging adults and those with PD learned the fixed sequence, but not the probabilistic sequence, indicating age-related impairments in probabilistic motor sequence learning. We found cortical activations indicative of learning, even in the absence of behavioral indications suggesting that some adults may require more practice to learn the sequence, and possible compensatory mechanisms in patients with PD. Novel applications of these techniques prove effective for a deeper understanding of the dynamic motor learning process and provide evidence that impairments observed in patients with PD may be related more to the aging process than to Parkinson’s disease.
Subtask Control in Human Locomotion
(2014) Logan, David Michael; Jeka, John J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
Maintenance of upright posture during walking is one the most important tasks to ensure flexible and stable mobility, along with speed adjustment, wayfinding and obstacle avoidance. These underlying functions, or subtasks, are simultaneously coordinated by the nervous system, which relies heavily on sensory feedback to obtain continual estimates of self-motion. This dissertation reports the findings of four experiments which made use of visual and mechanical perturbations to probe the interplay of these subtasks during treadmill walking. To confront the inherent nonlinearity of human gait, novel frequency domain analyses and impulse response functions that take into account phase of the gait cycle were used to characterize perturbation-response relationships. In the first experiment, transient visual scene motion was used to probe how visual input simultaneously influenced multiple subtasks, but at different phases of the gait cycle. In the second experiment, kinematics and muscle activity response variables showed an amplitude dependency on visual scene motion during walking that indicates vision is reweighted in a manner similar to standing posture. The third experiment used a metronome to constrain walking, revealing two time scales of locomotive control. The final experiment made use of both visual and mechanical perturbations simultaneously to probe the subtasks of postural orientation upright and positional maintenance on the treadmill. Doing so revealed that the nervous system prioritizes control of postural orientation over positional maintenance. In sum, this dissertation shows that sensory and mechanical perturbations provide insight as to how the nervous system controls coexisting, underlying functions during walking.

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