Jane M. Macpherson

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Recently developed computational techniques have been used to reduce muscle activation patterns of high complexity to a simple synergy organization and to bring new insights to the long-standing degrees of freedom problem in motor control. We used a nonnegative factorization approach to identify muscle synergies during postural responses in the cat and to(More)
We recently showed that four muscle synergies can reproduce multiple muscle activation patterns in cats during postural responses to support surface translations. We now test the robustness of functional muscle synergies, which specify muscle groupings and the active force vectors produced during postural responses under several biomechanically distinct(More)
1. Postural reactions were studied in six cats subjected to small, linear translations of the supporting surface in each of 16 different directions in the horizontal plane. Directions were specified in a polar coordinate system, with posterior translations being 0 degrees and leftward translations, 90 degrees. The data consisted of the forces exerted by(More)
1. This study tested the hypothesis that muscle synergies underlie the invariance in the direction of corrective forces observed following stance perturbations in the horizontal plane. Electromyographic activity was recorded from selected forelimb and hindlimb muscles of cats subjected to horizontal translations of the supporting surface in 16 different(More)
1. This study examined the relation between electromyographic (EMG) activation and the contact force and joint torques of the left hindlimb during postural equilibrium tasks in the standing cat. It is the appropriate application of force by the limbs against the support surface that allows the animal to control its center of mass and maintain equilibrium.(More)
The supplementary motor area of threeMacaca fascicularis was mapped using intracortical microstimulation (ICMS). Both forelimb and hindlimb movements were evoked using currents of 30 μA or less. However, thresholds for evoking movements were higher than those in the primary motor cortex. Proximal motor effects predominated, but distal joint movements were(More)
1. The purpose of this study was to examine the effect of changing initial stance conditions on the postural response of the cat to horizontal plane translations of the support surface. Cats were trained to stand, unrestrained, on a moveable force platform. The platform was translated linearly in each of 16 directions in the horizontal plane, with a(More)
The purpose of this study was to investigate the determinants of postural orientation by examining stance kinematics and kinetics at various interpaw distances. Four adult cats were trained to stand, unrestrained, on a force platform. Three-dimensional ground reaction forces and kinematics, as well as EMG activities, were recorded during stance at five(More)
The biceps femoris (BF) muscle is divided into three neuromuscular compartments defined by the innervation patterns of the main nerve branches (English and Weeks 1987). The goals of this study were i) to determine how different regions of the biceps femoris muscle are activated in the intact cat during a broad range of limb movements evoked by perturbations(More)
The purpose of this study was to determine the source of postural instability in labyrinthectomized cats during lateral head turns. Cats were trained to maintain the head in a forward orientation and then perform a rapid, large-amplitude head turn to left or right in yaw, while standing freely on a force platform. Head turns were biomechanically complex(More)