Studies into reaching have typically looked at the reaching arm or the eyes alone, ranging from single actions performed in controlled lab settings to a series of actions completed in natural environments. The current experiment looked at measures of the hand, arm and eyes as a right-handed subject performed a single reach and grasp action among real objects with their right hand. Specifically, this experiment was designed to investigate the impact of a potential non-target object (NTO) in the reach space on eye-hand coordination. Results showed that NTOs contralateral to the reaching arm produced almost no effects, whereas those ipsilateral became more “invasive” as they were located nearer a subject. Ipsilateral NTOs also produced a shift away from their location in fixation and grasp location on a target. These results suggest the brain used an “attention-for-action” system that highlighted locations as they became more relevant to the task.

Studies into reaching have typically looked at the reaching arm or the eyes alone, ranging from single actions performed in controlled lab settings to a series of actions completed in natural environments. The current experiment looked at measures of the hand, arm and eyes as a right-handed subject performed a single reach and grasp action among real objects with their right hand. Specifically, this experiment was designed to investigate the impact of a potential non-target object (NTO) in the reach space on eye-hand coordination. Results showed that NTOs contralateral to the reaching arm produced almost no effects, whereas those ipsilateral became more “invasive” as they were located nearer a subject. Ipsilateral NTOs also produced a shift away from their location in fixation and grasp location on a target. These results suggest the brain used an “attention-for-action” system that highlighted locations as they became more relevant to the task.

This study examined the generalization of the Dynamic Dominance Hypothesis (DDH) in regard to limb dominance, limb selection, and limb action. This study was inspired by the finding that limb selection changes from dominant-arm to nondominant-arm occur around an object position of 80° for right-handers and 100° for left-handers after passing the body midline (90°) into contralateral hemispace. For Study 1 and Study 2, 10 right-handed and 10 left-handed adults participated and reaching with the right and left arms of right- and left-handers was made to each of nine targets using free-choice and forced-choice paradigms. The purpose of Study 1 was to determine the relationship between limb selection and the DDH among both handedness groups. Thus, Study 1 addressed the following questions: Can the DDH explain why people select their nondominant hand for reaching into their contalateral hemispace? Do predictions of the DDH hold for right- and left-handers? Our results suggest that control efficiency with regard to a reduction in degrees of freedom in reaching movements seems to be a more fundamental cause for the limb selection phenomenon rather than the DDH. Also, our data reveal that kinematic differences between right- and left-handers with regard to utilization of joints for reaching explain limb selection differences between both handedness groups. The aim of Study 2 was to extend generalization of the DDH using a wide range of movement speed. Thus, Study 2 addressed the following question: Do propositions of the DDH hold for a wide range of speeds? Our data indicate the DDH does not hold for either slow or fast speed in reaching movements. Rather, a change in kinematics with regard to utilization of joints in reaching movements is associated with movement speed. Considered together, our data indicate that the DDH is an inadequate explanation of differences in limb selection, limb dominance (handedness), and limb action (speed). Rather, our findings with regard to control efficiency seem to be more fundamental and justified explanations for limb differences in the control of reaching based on the context of our task.

Stroke is a condition that arises from partial or complete blockage of blood flow to parts of the brain. Upper limb impairments (sensorimotor deficits) usually occur as a result of stroke. Assessment and diagnosis of the resulting upper limb impairments is important for effective rehabilitation and proper recovery. In terms of assessment, current ordinal scale systems used are inherently subjective and incorporate coarse rating scores (Chedoke McMaster, Fugel Meyer test, etc.). These scores do not provide clinicians with information regarding the underlying impairments which is important for effective rehabilitation therapy. We investigated the use of a reaching task on a bi-lateral upper limb robotic device (KINARM), developed by one of our team members (Stephen Scott), to assess upper limb impairments due to stroke. Control and stroke subjects were instructed to reach with both arms on the robotic device to illuminating spatial targets as quickly and as accurately as possible. We first developed a tool that would aid in locating targets where reaching impairments are visible for stroke subjects. From the Kinematic data collected, we then selected reaction time and first peak velocity of the hand and investigated their potential for separating control and stroke subjects. Results of our analysis showed the potential of both parameters as good quantitative assessment measures. In particular results for reaction time presented symmetrical differences between both arms were of main interest in this thesis. Such differences presented the potential of sensitivity in showing subtle impairments. / Thesis (Master, Computing) -- Queen's University, 2007-09-25 11:54:00.694

Posterior Cortical Atrophy (PCA) is a rare clinical syndrome characterised by the predominance of higher-order visual disturbances. Deficits result from a progressive neurodegeneration of occipito-temporal and occipito-parietal cortices. Due to its relative scarcity, many common symptoms of PCA, such as visuomotor dysfunction, have yet to be fully investigated. The current study sought to explore the visuomotor abilities of four individuals with PCA by testing their ability to reach out and grasp real objects under various viewing conditions. The patients demonstrated many of the same deficits as those seen in individuals with optic ataxia, including impaired grip scaling to peripheral targets, poor selection of stable grasp sites, and evidence of ‘magnetic misreaching’ – a pathological reaching bias towards the point of visual fixation. Unlike individuals with pure optic ataxia, however, the patients in the current study showed symptoms indicative of damage to the ventral stream of visual processing, including abolished grip scaling during memory-guided grasping and an inability to differentiate objects based on their shape. This research increases our understanding of the visuomotor deficits associated with PCA. It also adds to our knowledge of how visual information is processed in the brain, including the complex interaction between vision for action and vision for perception.

Posterior Cortical Atrophy (PCA) is a rare clinical syndrome characterised by the predominance of higher-order visual disturbances. Deficits result from a progressive neurodegeneration of occipito-temporal and occipito-parietal cortices. Due to its relative scarcity, many common symptoms of PCA, such as visuomotor dysfunction, have yet to be fully investigated. The current study sought to explore the visuomotor abilities of four individuals with PCA by testing their ability to reach out and grasp real objects under various viewing conditions. The patients demonstrated many of the same deficits as those seen in individuals with optic ataxia, including impaired grip scaling to peripheral targets, poor selection of stable grasp sites, and evidence of ‘magnetic misreaching’ – a pathological reaching bias towards the point of visual fixation. Unlike individuals with pure optic ataxia, however, the patients in the current study showed symptoms indicative of damage to the ventral stream of visual processing, including abolished grip scaling during memory-guided grasping and an inability to differentiate objects based on their shape. This research increases our understanding of the visuomotor deficits associated with PCA. It also adds to our knowledge of how visual information is processed in the brain, including the complex interaction between vision for action and vision for perception.

Long-term potentiation (LTP), a long-lasting enhancement of synaptic efficacy, is believed to be the mechanism by which memory storage occurs in the brain. Several studies have shown that LTP can be induced in various neural sites, not only by electrical stimulation, but also as a result of behavioural modifications. It has previously been shown that LTP in the primary motor cortex accompanies motor skill learning. One study showed that potentiation occurred following training on a lateralised skilled reaching task. In this task, animals are trained to use only one paw to grasp a small food pellet. An interesting finding that has been uncovered from these studies is that, although only one hemisphere actively participates in the task (the trained hemisphere), the other hemisphere (untrained hemisphere) also shows potentiation. This has led to the hypothesis that the corpus callosum is involved in the transfer of information from one hemisphere to another during training on the reaching task. The nature of this communication, however, is unknown. Two possibilities were considered. The first was that the callosum transfers information that allows the animal to maintain its balance while the reaching paw is elevated. Careful observation of videorecording made while animals performed the task however, failed to reveal any deficits in balance in animals that had undergone a callosal transection. A second possibility is that the corpus callosum transfers information about the task from the trained to the untrained hemisphere such that, even though it does not actively participate in the task, the untrained paw may "know" how to perform above chance level. Analysis of the rate of successful reaching with the untrained paw revealed no advantage for normal animals over transected animals. Work is however, currently underway to increase the number of animals in the study in order to obtain a more conclusive result. / Thesis / Master of Science (MS)

Injury to the cervical spinal cord is a devastating event that results in a transient to permanent loss of sensory and motor functions following injury. Moderate recovery has been reported to occur in individuals and in animal models after spinal cord injury (SCI). One approach to promote recovery after SCI is rehabilitative training. This thesis examines the relation of reaching training with adaptive changes (i.e. plasticity) and functional recovery following SCI. In my first experiment, I investigated whether plasticity of the corticospinal tract (CST) is the cause for reaching recovery after ablation of the dorsal and lateral CST. Rats that received reaching training were significantly better in reaching than their untrained counterparts. A relesion of the CST revealed that the reaching recovery mainly depended on plasticity of the CST itself. Since it is controversial whether training should be initiated immediately after SCI, I investigated whether a delayed initiation of reaching training after SCI is beneficial. I compared the reaching success of rats that received reaching training on day 4 post SCI with rats that received training on day 12 post SCI. I found that the reaching success in rats that either received reaching training on day 4 or 12 following SCI was similar. Lastly, I investigated whether training efficacy is declined in chronically injured rats. Since it has been shown that the inflammatory response after SCI declines, it is questionable whether there is a relation between the inflammatory response after SCI and training efficacy. In my last experiment I injected chronically injured rats with a substance that induces a systemic inflammation. I found that rehabilitative reaching training in chronic injured rats only resulted in an improved reaching recovery when the training was combined with the administration of the substance that induces inflammation (lipopolysaccharide). Although there are still unanswered questions regarding the underlying mechanism for functional recovery after SCI, the results of this thesis could be used as a basic to improve future rehabilitative training strategies and therefore improve the quality of life in individuals that suffer from SCI.

Previous studies found that providing infants with repeated opportunities for reaching improved the emergence and quality of the behavior, presumably via exploratory and selective processes (Bojczyk & Corbetta, 2004; Lobo et al., 2008). Here we further examined the effects of opportunities for reaching by exposing infants to multimodal objects that were activated either continuously by a hidden motor or contingently by hand-toy contact. We asked if such objects would motivate infants to try to reach for them even more than still and silent objects. Forty-four pre-reaching infants were recruited within the week prior to turning three months of age and were seen for 16 consecutive days. Three groups received daily exposure to objects that either moved and made noise continuously (continuous), moved and made noise only on hand-object contact (contingent), or did not move or make noise when touched (repeated task exposure). A control group received no daily experience. On day 1, all infants were assessed in the laboratory to ensure they were not reaching. From days 2-15, an experimenter tested the repeated groups in the home. On day 16, all infants’ reaching was reassessed in our laboratory. Arm kinematics were recorded during laboratory visits. All testing was the same: infants were seated in an infant chair behind a table and an experimenter placed 1 toy on the table at midline for one minute. Infants received ten trials per day. We measured amount of intentional reaches, hand-toy distance, and peak movement speed. Intentional reaching significantly increased for all repeated groups. Examination of infants that improved showed that the contingent group displayed a significantly higher gain in reaching over time relative to the repeated task exposure and continuous groups. Kinematic measures indicated that these young infants modulated the speed of their reaching movements to match task demands. Specifically, infants in the continuous group displayed increased peak speeds of their movements in order to contact a moving object. Results suggest that repeated opportunities to reach for objects underlies the emergence of reaching; however this process may be aided by providing a salient, multimodal link that highlights the effects of successful action.

Stroke is the leading cause of long-lasting disability in the United States and disproportionately affects adults in later life. Age-related decreases in dexterity and neural plasticity may contribute to the poorer prognosis of older stroke survivors, even following rehabilitative physical therapy. The goal of these dissertation studies is to determine how the cortical plasticity underlying motor skill learning, both before and after brain injury, changes in the aged brain. The general hypothesis of these studies is that age-related changes in motor performance and the limited ability to regain function following brain injury are associated with dysfunctional plasticity of the forelimb representation in the motor cortex. This hypothesis was tested in intact C57BL/6 mice by training them on a skilled reaching task and deriving intracortical microstimulation evoked motor cortical representations of the forelimb to determine training-induced changes in the function of the motor cortex. After ischemic lesions, age-dependencies in the effects of rehabilitative training in skilled reaching on forelimb motor cortical representations were investigated. Prior to injury, intact young and aged mice learned a skilled reaching task in similar time frames and with similar success rates. Training-induced reorganization in the young mouse motor cortex occurred in the caudal forelimb area, which is homologous to the primary motor cortex of primates. However, the rostral forelimb area, a potential premotor cortex, was larger in aged mice compared to young mice. Following focal ischemic lesions of the forelimb area of the sensorimotor cortex, aged mice had larger lesions and were more impaired than young mice, but both groups regained reaching ability after 9 weeks of rehabilitative training. Post-operative training resulted in plasticity of the rostral forelimb area in young mice, but we failed to see reorganization in the forelimb map of aged mice following rehabilitative training. These dissertation studies suggest that more severe brain damage in response to ischemia leads to poorer outcome in aged animals. Although the reorganization of motor cortex following initial skill learning and relearning following brain damage changes with age, the ability to learn motor tasks and improve function with rehabilitative training is maintained in healthy aging. / text