Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item 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.Item Understanding Neuroplastic Effects of Transcranial Direct Current Stimulation through Analysis of Dynamics of Large-Scale Brain Networks(2012) Venkatakrishnan, Anusha; Contreras-Vidal, José L.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intrinsic adult neuroplasticity plays a critical role in learning and memory as well as mediating functional recovery from brain lesions like stroke and traumatic brain injuries. Extrinsic strategies to aid favorable modulation of neuroplasticity act as important adjunctive tools of neurorehabilitation. Transcranial direct current stimulation (tDCS) is an example of a non-invasive technique that can successfully induce neuroplastic changes in the human brain, although the underlying mechanisms are not completely understood. In this regard, characterization of neuroplastic changes in large-scale brain networks is a functional and necessary step towards non-invasively understanding neuroplastic modulation mediated by tDCS in humans. This dissertation, thus, aimed to understand the effects of tDCS, on large-scale brain network dynamics recorded through magnetoencephalography (MEG) through three specific aims that will provide novel insights into the mechanism(s) through which plastic changes are promoted by tDCS, specifically in the context motor learning. This dissertation pursued a systematic investigation of these changes in whole-head cortical dynamics using both model-free and model-based analysis techniques. Two experiments were conducted to dissociate between network changes mediated by tDCS at rest as well as when coupled with a task in order to determine optimal conditions for using tDCS for clinical purposes. Results from Study 1 using model-free analysis showed that a specific fronto-parietal network at rest was modulated up to a period of 30 minutes outlasting the duration of the stimulation. Further model-based analysis of this fronto-parietal network showed that these differences were driven by network activity primarily involving high frequency gamma band connectivity to and from the supplementary motor area to associated regions (left primary motor cortex (stimulated region), left prefrontal and parietal cortices). Results from Study 2 showed that the tDCS exerts highly polarity-specific effects on the impact of oscillatory network connectivity, within the functionally relevant fronto-parietal network, on behavioral changes associated with motor learning. These results advance our understanding of neuroplasticity mediated by tDCS and thus, have implications in the clinical use of tDCS for enhancing efficacy of neurorehabilitation in patients with stroke and traumatic brain injury.