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Browsing by Subject "Motor control"

Now showing 1 - 6 of 6
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    Characteristic information required for human motor control:Computational aspects and neural mechanisms.
    (2010-08) Christopoulos, Vassilios N.
    Motor behavior involves creating and executing appropriate action plans based on goals and relevant information. This information characterizes the state of environment, the task and the state of actions performed. The perceptual system gathers this information from different sources: touch, vision, audition, scent and taste. Despite the richness of environment and the sophistication of our sensory system, it is not possible to extract a complete and accurate representation of the required states for motor behavior because of noise and ambiguity. Consequently, people effectively have “limited information” and therefore may not be certain about the outcomes of specific actions. For motor behavior to be robust to uncertainty, the brain needs to represent both relevant states and their uncertainties, and it needs to build compensation for uncertainty into its motor strategy. Generating motor behavior requires the brain to convert goals and information into action sequences, and the flexibility of human motor behavior suggests that brain implements a complex control model. The primary goal of this work is to improve the characterization of this control model by studying motor compensation for uncertainty and determining the neural mechanisms underlying information processing and the control model. Part of this thesis focuses on studying human compensation strategies in natural tasks like grasping. We experimentally tested the hypothesis that people compensate for object position uncertainty by adopting strategies that minimize the impact of uncertainty in grasp success. As we hypothesized, we found that people compensate for object position uncertainty by approaching the object along the direction of maximal position uncertainty. Additionally, we modeled the grasping task within the optimal control framework and found that human strategies share many characteristics with optimal strategies for grasping objects with position uncertainty. We are also interested to understand how the brain encodes and processes information relevant to movements. To accomplish this, we studied the spatial and temporal interactions of cortical regions underlying continuous and sequential movements using magnetoencephalography (MEG). Particularly, we took data from a previous study, in which subjects continuously copied a pentagon shape for 45 s using an XY joystick. Using Box-Jenkins time series analysis techniques, we found that neural interactions and variability of movement direction are integrated in a feedforward-feedback scheme. MEG sensors related to feedforward scheme were distributed around the left motor cortex and the cerebellum, whereas sensors related to feedback scheme had a strong focus around the parietal and the temporal cortices.
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    Computational studies of cerebellar cortical circuitry
    (2013-05) Popa, Laurentiu Silviu
    This thesis includes two directions of research regarding the function and physiology of the cerebellum. One direction was concentrated on the cerebellum involvement in motor control during a visually guided tracking task performed by non-human primates. The second effort aimed to characterize the effects of the P/Q-type Ca2+ channelopathy on the physiology of the cerebellar cortex in tottering mice and to explore the mechanisms that transform homeostatic deficits due to genetic mutations into transient phenotype such as episodic dystonia. Understanding the cerebellum function is an ongoing challenge. The cerebellum has been implicated in error processing required for on-line motor control and motor learning. The dominant view is that the error related signals are encoded by the Purkinje cell complex spike discharge. The results presented in this thesis show that the Purkinje cell simple spike activity robustly signals a rich representation of task specific performance errors, independently from the kinematic signals. The results also show that a large majority of the Purkinje cells encode behavioral parameters dually by a pair of signals, one predictive and one feedback related. The predictive signals could provide the neural substrate for the feedback-independent compensatory movements that maintain motor behavior accuracy. The dual representation is also consistent with the signals needed to generate the prediction sensory error used to update an internal model. These results provide new insights into the cerebellum function and have interesting implications for the forward internal model hypothesis. The tottering mouse is an autosomal recessive disorder involving a mutation in the gene encoding the P/Q-type Ca2+ channels and is one of the animal models for the episodic ataxia type 2. The most remarkable aspect of the tottering mouse phenotype are the transient attacks of dystonia triggered by stress, ethanol or caffeine. The neural processes underlying the transient phenotype are unknown. The results presented in this thesis, based on the flavoprotein autofluorescenece imaging, show that the tottering mouse dysfunction is associated with the presence of transient synchronous low frequency oscillations in the cerebellar cortex. For a large majority of cerebellar cortical neurons the optical oscillations reflect the oscillations present in their spontaneous activity. The oscillations appear to be intrinsic to the cerebellar cortex and in the awake animals increased oscillatory cerebellar activation becomes highly coherent with the EMG activity during episodic dystonia. Low frequency oscillations of the cerebellum represent a novel abnormality in the tottering mouse and could provide insights into the mechanism underlying the transient phenotype of the episodic ataxia type 2.
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    Encoding and control of motor prediction and feedback in the cerebellar cortex
    (2017-08) Streng, Martha
    Extensive research implicates the cerebellum as a forward internal model that predicts the sensory consequences of motor commands and compares them to their actual feedback, generating prediction errors that guide motor learning. However, lacking is a characterization of how information relevant to motor control and sensory prediction error is processed by cerebellar neurons. Of major interest is the contribution of Purkinje cells, the primary output neurons of the cerebellar cortex, and their two activity modalities: simple and complex spike discharges. The dominant hypothesis is that complex spikes serve as the sole error signal in the cerebellar cortex. However, no current hypotheses fully explain or are completely consistent with the spectrum of previous experimental observations. To address these major issues, Purkinje cell activity was recorded during a pseudo-random manual tracking task requiring the continuous monitoring and correction for errors. The first hypothesis tested by this thesis was whether climbing fiber discharge controls the information present in the simple spike firing. During tracking, complex spikes trigger robust and rapid changes in the simple spike modulation with limb kinematics and performance errors. Moreover, control of performance error information by climbing fiber discharge is followed by improved tracking performance, suggesting that it is highly important for optimizing behavior. A second hypothesis tested was whether climbing fiber discharge is evoked by errors in movement. Instead, complex spikes are modulated predictively with behavior. Additionally, complex spikes are not evoked as a result of a specific ‘event’ as has been previously suggested. Together, this suggests a novel function of complex spikes, in which climbing fibers continuously optimize the information in the simple spike firing in advance of changes in behavior. A third hypothesis tested is whether the simple spike discharge is responsible for encoding the sensory prediction errors crucial for online motor control. To address this, two novel manipulations of visual feedback during pseudo-random tracking were implemented to assess whether disrupting sensory information pertinent to motor error prediction and feedback modulates simple spike activity. During these manipulations, the simple spike modulation with behavior is consistent with the predictive and feedback components of sensory prediction error. Together, this thesis addresses a major outstanding question in the field of cerebellar physiology and develops a novel hypothesis about the interaction between the two activity modalities of Purkinje cells.
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    Goal selection as a control strategy in a brain-computer interface
    (2011-09) Royer, Audrey Nicole Smith
    A brain-computer interface (BCI) translates signals recorded directly from the brain into commands that control an external device, such as a computer cursor, wheelchair, or neuroprosthetic. BCIs promise to help the nearly 6 million people who live with paralysis by allowing them to interact with the world in ways they are no longer able. BCIs can also be used by able bodied individuals to extend their capabilities. BCIs differ widely in how they implement the translation from raw brain signal to device command. Two competing control strategies, goal selection and process control, differ in how much the BCI assists the user. In process control, the user controls every step of the process and receives minimal to no assistance from the system. Other terms for process control include low-level control or continuous control. In goal selection, the user only needs to determine the goal and the system executes the process to achieve that goal. Other terms for goal selection include high-level control or shared control. This thesis presents the first studies directly comparing goal selection and process control. We found in these studies that the goal selection based paradigms were easier to learn, had a decreased training period, and provided improved speed, accuracy, and information transfer in both the simple and more complex applications studied. This thesis also extends our understanding of the neurophysiology while using a sensorimotor rhythm based BCI. When individual trial data were analyzed and not averaged as is typically done in the literature, we found that duration of sensorimotor rhythm modulation was more correlated to successful use than amplitude of modulation. Additionally, we found that correct modulation that led to either a single hit or overall high accuracy was the same between the two control strategies. This shows that the improved performance in these studies while using the goal selection based paradigms was more attributable to the difference in device command instead of the difference in raw brain signal. By understanding neurophysiology and applying that knowledge to BCI design, we can make a better BCI.
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    Movement Control And Cortical Activation In Functional Ankle Instability
    (2008-07) Anderson, Kathleen Marie
    Background: Functional ankle instability (FI) is a common development following first-time lateral ankle sprain, resulting in functional limitations. Local tissue damage has not been a satisfactory explanation. Evidence exists of changes in motor control within the central nervous system in individuals with FI. Further investigation of the nature of these changes is warranted. Methods: Twenty subjects with FI and twenty healthy control subjects allowed comparisons between ankles within groups and between groups. Two primary methods of investigation were used. A kinematic analysis using electromagnetic motion capture was used during a step down task to assess repeatability and variation in patterns of ankle dorsiflexion/plantarflexion and inversion/eversion motion and speed and phase timing characteristics. A normalized coefficient of multiple correlations was used for motion cycle comparisons, and means and variance were compared for discreet time variables. Motor control was measured with an accuracy index from an ankle tracking task. A sub-group of 8 right-involved FI subjects and 10 control subjects underwent functional magnetic resonance imaging to detect cortical activation in sensorimotor areas while performing the tracking task. Results: With the step down task no between-group differences in the repeatability of ankle motions were found, although both groups showed greater variability in inversion/eversion than dorsiflexion/plantarflexion. Increased ankle instantaneous angular speed when contacting the step was found in the FI subjects, with trends to reversing instantaneous linear velocity and more rapid weight acceptance also noted. No differences in tracking accuracy were identified; however, differential patterns of lateralization of cortical activation were found within groups between ankles during the task, with greater contralateral hemisphere activity in the primary motor area and more symmetrical activity in the primary sensory cortex (S1) and supplementary motor areas in FI subjects tracking with the involved ankle than was observed in control subjects tracking with the right ankle. Between-group comparisons found areas of greater activation in left S1, premotor cortex, and anterior cingulate gyrus compared to control subjects. Conclusions: The results of this study support that processing differences exist at the cortical level between FI and healthy control subjects. Motor performance differences are also present.
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    Movement sequences based on temporal interval duration and spatial position and neuronal activity in macaque dorsolateral prefrontal cortex
    (2014-11) Kerrigan, Stephen
    In neural and imaging studies the Dorsolateral Prefrontal Cortex (DLPFC) has each been shown to participate in encoding the passage of time, as well as spatial movement sequences. But we do not know how time, space, and serial order are encoded during more complex behaviors that require simultaneous control over all of these elements. In this thesis non-human primates were trained to perform a complex spatio-temporal sequence task comprised of three directional arm movements that were followed by three self-timed temporal delay intervals. We recorded single neurons in the DLPFC of two animals during performance of this task. We found evidence the single cells encoded information about the serial order, temporal interval, and direction of each movement as independent quantities as well as a joint aggregate.