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Colliding with objects in our environment is a common feature of daily activity. Skilled behaviour often involves the precise regulation of these collisions. Traditional approaches to skilled behaviour are criticised for confusing the constraints of their approach with behavioural constraints. The following investigation combines aspects of several approaches laid out in the Introductory Chapter 1 to examine the visual and motor processes involved in controlling collisions. In Chapter 2 performance is assessed in a one-handed catching task, when the physical characteristics of the ball are manipulated. The results indicate that viewing-time and the nature of grasping affect perfomance. In Chapters 3 and 4 a hitting task is used to investigate the visual processes involved in intercepting an object. Task performance is compared across monocular and binocular viewing conditions. In Chapter 3, results show that timing performance is unaffected by this manipulation and this provides support for the direct pick up of time-to-collision information. In Chapter 4, binocular information is found to be necessary for the spatial location of an object. In Chapters 5, 6 and 7, a tapping task is used to investigate the motor aspects involved in controlling a collision. In Chapter 5 force waveforms recored when tapping on a strain gauge vary in accordance with 'external' and 'internal' manipulations of load and stiffness. In Chapter 6, a mass-spring model is proposed to describe the collision. Changes in impact are related to changes in the parameters of the model. These effects are simulated on a computer. In Chapter 7, the mechanisms of effecting collision change are directly investigated from kinematic recordings. The results suggest that speed of impact is the controlled parameter. The findings are compatible with the mass-spring model. The final Chapter concludes that a multi-dimensional approach is required for a full understanding of skilled-motor behaviour. The possible applications of this approach to the assessment of clumsiness are discussed.

The ability to perform precise and relatively independent movements of the fingers is an important feature of the primate's motor repetoire. A substantial amount of evidence suggests a special role for the hand area of the motor cortex in the execution of these movements, and in particular, thoses cells which make direct cortico-motoneuronal connections with motoneurones innervating the hand muscles. The axons of these corticomotoneuronal (CM) cells form part of the pyramidal tract. The subject of this study is the influence of these CM cells upon the activity of hand muscles in the conscious monkey performing a precision grip task between thumb and index fingers. Three aspects of the cortico-motoneuronal connection have been investigated; 1. The effect of discharges in individual CM cells on the gross e.m.g. activity of intrinsic hand and forearm muscles, and the distribution of these effects over various muscles. 2. The effect of individual CM cell discharge on the single motor unit activity in the intrinsic thumb muscles. 3. The significance of differences in firing frequency of individual CM cells upon their modulation of gross e.m.g. The spike-triggered averaging technique was employed to study the overall effect of identified pyramidal tract neurones (PTN) on gross e.m.g. activity. Rectified gross e.m.g. was averaged with respect to the discharges of single PTNs. The influence of the triggering cortical cell was revealed in the averages as a transient increase in muscle activity at the appropriate time after the cell had fired. This effect is called post-spike facilitation (PSF). The occurance of PSF in the spike-triggered average was taken as evidence that the triggering cells made a direct, presumably monosynaptic, connection with the motoneurones of the muscle in question. Quantitative and qualitative aspects of PSF are discussed. The activity of 5 to 10 intrinsic hand and forearm muscles were averaged with respect to individual PTNs. In this way the PSF distribution over different muscles, produced by one cortical cell, could be determined. It was established that CM cells produce PSF in a relatively restricted number of muscles (2-3 out of 10 tested). The impact of CM cells on the discharge activity of single motor units was studied by cross-correlating both spike trains. To overcome the considerable sampling problem, the occurrence of PSF in the spike-triggered gross e.m.g. average was used as a criterion for further cross-correlation analysis. The cross-correlogram peaks half-width and onset latency were suggestive for monosynaptic excitation of the motoneurones. Different approaches are discussed to estimate the strength of these connections and to relate these strengths to the number of synpatic boutons that the CM cell makes upon its target motoneurones. In terms of the number of extra discharges fired by the single motor unit in response to CM cell firing, the effects can be described as weak (5-20 extra motor unit spikes per 1000 CM cell discharges). It was possible to study the connectivity of single CM cells with different motor units of the same muscle by simultaneously recording several (2-5) motor units. It was found that if a CM cell showed a correlogram peak with one of the concurrently sampled motor units, most other motor units sampled from the same muscle would give correlogram peaks with the same CM cell. This finding is suggestive for a rather diffuse collateralization of the CM cell axons within the motoneurone pool of the target muscle. Finally the influence of different firing frequencies of CM cells on the form and strength of PSF effects was investigated. A striking result was that discharges preceded by long interspike intervals (> 50ms)could still exert quite powerful excitatory effects. The results of this series of experiments further elucidate the nature of the corticomotoneuronal connection and give an impression of the facilitatory capacity of single CM cells on motoneurons innervating the hand muscles.

The series of experiments reported in this thesis concern the ability to make perceptual-motor judgements of distance (Ex. 1 to Ex. 7) and size (Ex. 8). Experiments 1 and 2 indicated that visual judgements of maximum step length were effected by; distance from the site of action, the angle at which the obstacle was presented and whether monocular or binocular vision was used. This suggested that perceived maximum ability was not based on a body scaled invariant as suggested by Gibson (1979). Experiments 3 and 4 were designed to investigate the effect of altering the length of distance to-be-remembered, and compared performance across both visual and kinaesthetic conditions. The results suggested that the reproduction of distance is normally based on memory for the location of the end point, rather than the extent of the distance. No support was found for the claim that differences between the accuracy of recall of location and extent was due to the differential rehearsability of visual and kinaesthetic codes. Instead, it was proposed that changes in the procedure may have influenced performance by reducing the usefulness of a 'landmark' based form of coding in the extent trials. Experiments 5 and 6 were designed to investigate predictions arising from one of the dominant models of cross-modal performance (Connolly and Jones, 1970). Connolly and Jones's model postulated that differences between intra- and cross-modal performance could be explained in terms of the characteristics of modality specific short-term storage codes, and that translation between codes occurs prior to short-term storage. In general the results obtained were supportive of the pattern of accuracy reported by Connolly and Jones. However, the effect of delaying until the end of the retention interval knowledge of the reproduction mode was inconsistent with the model, that is, withholding information about the required reproduction mode appeared to increase the accuracy of judgements. One explanation for this effect is that pre-translated information was held in a form which was associated with high levels of both accuracy and attention. This speculative explanation was seen to have parallels with the Working Memory model (Baddeley and Hitch, 1974). Experiments 7 and 8 used an interference task paradigm to investigate whether a separate visuo-spatial store could be demonstrated to exist in relation to perceptual-motor information. The results failed to find conclusive support for such a store. The cumulative findings of Experiments 1 to 8 are discussed in relation general models of perceptual-motor performance.

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Many reasons can be cited for resorting to motor behaviour science in psychology as a departure point for investigating piano technique. This study compares the merits of the motor and action systems approaches to motor control and learning in order to assess which approach could be most valuable in addressing problems of piano playing. The study commences with an investigation into the traditional motor systems perspective of motor control. Discussions are rather general and multi-faceted in order to enhance understanding of action theorists' criticisms of the motor view- an approach also necessitated by the lack of research involving piano playing. Three stages of human information-processing and the way they are influenced by interference are examined. In the final, i.e. response-programming stage, movements can only be launched in discrete bursts; this, however, does not influence fluency and continuity in piano playing, because a response can consist of many subsidiary movements controlled by a motor program. In the response-execution stage following information-processing, movements are organized with a powerful underlying temporal structure. Only one such structure can be sustained by the motor program at a time, explaining the difficulty of executing polyrhythms in piano playing. The generalized motor program concept can account for certain easily coordinated technical constructs in piano playing. Also, grounds exist for postulating that rhythm and timing in piano playing are regulated by an internal clock. Following discussions on the relative importance of three types of intrinsic feedback for piano playing and the pointing out of techniques for giving extrinsic feedback, Adams's closed-loop theory and Schmidt's schema theories for motor learning under the motor systems approach are critically examined. Methods are described for applying schema theory concepts to musical instrument practice. Motor memory, apparently, is not well understood. Action theorists regard the motor systems application of the computer metaphor to human motor behaviour and the motor programming notion as incorrect. The concept of functionally-defined actions consisting of postures and movements, which in themselves are actions, is presented. The ecological view, based on Gibson, that human information-pickup from the environment is direct, without elaborate central processing, is discussed. Apparent common denominators between two prominent "methods" for piano playing and action systems theory are pointed out. Most aspects of action systems theory still need to be tested; much uncertainty is also prevalent on action learning. Under the motor systems approach, various scientifically-based premises exist for structuring piano practice, applying to inter alia massed vs. distributed practice, blocked vs. random practice, variability in practice, slow practising of rapid passages, and practising "in rhythms". If action theory is correct in that the motor programming notion is wrong, most of these premises could lose their scientifically-based claims to validity; so will schema theory. Unfortunately, action theory apparently cannot offer any scientifically verified alternatives yet. Much more research will be necessary for either choosing a particular theory or establishing a fusion between theories as a basis for piano-technical learning. / Dissertation (MMus)--University of Pretoria, 2012. / Music / unrestricted

Maged1 appartient à la famille des gènes Mage (pour Melanoma antigen gene). Bien que les gènes Mage aient tout d'abord été découverts dans des cellules tumorales, le gène Maged1 est également exprimé dans un grand nombre de tissus sains et particulièrement dans le système nerveux central, aussi bien au cours du développement que chez l'animal adulte. Les fonctions exercées par la protéine Maged1 dans le système nerveux restent actuellement fort méconnues bien que des études aient pu mettre en évidence son implication dans des processus tels que l'homéostasie du rythme circadien, certaines formes d'apprentissages, les comportements sociaux et sexuels ainsi que dans des pathologies telles que la dépression et l'obésité. Au laboratoire, nous avons pu montrer que la délétion de l'allèle Maged1 chez la souris cause une diminution d'activité locomotrice spontanée et un déficit de coordination motrice. Les animaux ne possédant plus l'allèle Maged1 montrent également une absence complète de réponse à l’administration de drogues comme la cocaïne et la morphine. Au cours de ce travail de thèse, nous avons recherché les mécanismes liant le gène Maged1 et ces comportements. La dopamine étant un neurotransmetteur connu pour réguler à la fois les comportements moteurs et les comportements liés à la dépendance aux drogues, nous avons tout d'abord fait l'hypothèse qu'un déficit en dopamine pouvait expliquer les phénotypes observés. En effet, des expériences de microdialyse in vivo ont montré que l'augmentation de concentration en dopamine dans le nucleus accumbens suite à une injection de cocaïne était significativement réduite chez les souris dépourvues de l'allèle Maged1. L'implication directe de Maged1 dans la physiologie des neurones dopaminergiques a été étudiée par la génération de souris transgéniques dont la délétion du gène Maged1 a été ciblée spécifiquement dans ces neurones. Cependant, cette lignée de souris ne récapitule pas les phénotypes observés chez les souris entièrement dépourvues de l'allèle Maged1. Ces résultats indiquent que l'expression de Maged1 dans les neurones dopaminergiques n'est pas nécessaire au contrôle moteur et à la réponse comportementale à l'administration de cocaïne. Nous avons ensuite étudié les régions innervées par les neurones dopaminergiques en réalisant des enregistrements électrophysiologiques sur tranches de cerveaux en survie. Nous avons ainsi pu mettre en évidence une altération de la transmission glutamatergique entre le cortex préfrontal et le nucleus accumbens chez les souris dépourvues du gène Maged1. La délétion spécifique de l'allèle Maged1 dans chacune de ces deux régions a ensuite été effectuée. Les souris dont la délétion de Maged1 a été ciblée dans les neurones du striatum n'ont pas montré d'altération comportementales. Cependant, lorsque la délétion de Maged1 est effectuée spécifiquement dans le cortex préfrontal, les souris montrent un déficit d'apprentissage moteur ainsi qu'une réduction de l'effet de sensibilisation à des injections répétées de cocaïne. Chez ces mêmes souris, la réduction de sensibilisation est accompagnée d'une réduction de la réponse dopaminergique à la cocaïne telle qu'observée au cours d' expériences de microdialyse in vivo. Au cours de ce travail, nous avons donc pu montrer que la présence de la protéine Maged1 dans le cortex préfrontal est nécessaire à l'apprentissage moteur et à l'expression de la sensibilisation comportementale à la cocaïne. Cette protéine exerce probablement sa fonction en régulant la neurotransmission au niveau du compartiment présynaptique. / Doctorat en Sciences biomédicales et pharmaceutiques (Médecine) / info:eu-repo/semantics/nonPublished

Parkinson’s disease is a movement disorder characterized by nigrostriatal dopamine pathway degeneration and neuronal α-synuclein accumulation. Pathogenesis is associated with mutations in α-synuclein and Gba1 encoding alleles. Animal models created to date do not recapitulate the spectrum of clinical disease features. This thesis characterizes the bi-genic Synergy mouse, hypothesized to demonstrate motor behavioural and histological abnormalities downstream of α-synuclein overexpression and mutated Gba1. Synergy and SNCA mice (overexpressed α-synuclein with wild-type Gba1) have early onset deficits in motor coordination, muscle strength and nest building. Both exhibit increased α-synuclein concentration in the brain and cerebellar inclusions positive for two markers of pathological α-synuclein processing. Overall mutant Gba1 expression within Synergy mice does not worsen the behaviour or the histopathological findings associated with overexpression of human α-synuclein in SNCA mice. Future studies will determine whether mutant Gba1 expression alters cognitive behaviour and/or lipid homeostasis in this new bi-genic model of Parkinson’s disease.

No-vision walking is supported in the central nervous system (CNS) by a spatial updating process. This process involves the iterative updating of a mental representation of the environment using estimates of distance traveled gleaned from locomotive kinematic activity. An effective means of examining the online regulation of this process is a continuous pointing task, which requires performers to walk along a straight-line forward trajectory while keeping their right arm straight and index finger fixated on a stationary ground-level target beside the walking path. In the current thesis, no-vision continuous pointing was examined in typically calibrated and recalibrated perceptual-motor states. Shoulder and trunk joint angles provided the basis for perceptual measures that reflected spatial updating performance and kinematic measures that reflected its underlying CNS online regulation. In the typically calibrated conditions, no-vision walking demonstrated a slight perceptual underestimation of distance traveled (Study 1). In the recalibrated conditions, no-vision walking demonstrated: a) perceptual underestimation and overestimation following adaptation periods involving walking with low and high visual gains, respectively (Study 2); and b) partial recalibration following exposures to vision and arm gains (Study 3). The latter was suggested as being impacted by task specific changes in CNS multisensory integration resulting from the development of a robust task prior and/or the altering of sensory cue weights. Importantly, this thesis used a novel trajectory parsing procedure to quantify discrete CNS perceptual updating units in the shoulder plane of elevation trajectory. The starts and ends of these updating units were consistently timed to the late left-to-early right foot swing phase of the step-cycle, regardless of perceptual-motor state. This was suggested to reflect perceptual units that were purposely timed, but indirectly mapped, to this kinematic event. The perceptual differences in Studies 1 and 2 were at least partially reflected in these units. / Thesis / Doctor of Philosophy (PhD) / It is well understood that humans can effectively walk without vision to environmental locations up to 15 metres away. However, less is known about how these walking movements are controlled during the course of forward progression. This thesis fills this knowledge gap using a task that requires participants to walk forward along a straight path while keeping their right index finger pointed toward a ground-level target beside the walking path. The patterns of arm movements performed during this task are indicative of the control strategies used by the performer to mentally update their positions in space. One of the key contributions of this work is showing that humans perform this mental updating in a repetitive manner, and that these repetitions are consistently linked to early forward movements of the right leg. This pattern is maintained when walking without vision is performed in a variety of different contexts.