I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Principles of Neural Science

It is generally accepted that human bipedal upright stance is achieved by feedback mechanisms that generate an appropriate corrective torque based on body-sway motion detected primarily by visual, vestibular, and proprioceptive sensory systems. Because orientation information from the various senses is not always available (eyes closed) or accurate (compliant support surface), the postural control system must somehow adjust to maintain stance in a wide variety of environmental conditions. This is the sensorimotor integration problem that we investigated by evoking anterior-posterior (AP) body sway using pseudorandom rotation of the visual surround and/or support surface (amplitudes 0.5-8 degrees ) in both normal subjects and subjects with severe bilateral vestibular loss (VL). AP rotation of body center-of-mass (COM) was measured in response to six conditions offering different combinations of available sensory information. Stimulus-response data were analyzed using spectral analysis to compute transfer functions and coherence functions over a frequency range from 0.017 to 2.23 Hz. Stimulus-response data were quite linear for any given condition and amplitude. However, overall behavior in normal subjects was nonlinear because gain decreased and phase functions sometimes changed with increasing stimulus amplitude. "Sensory channel reweighting" could account for this nonlinear behavior with subjects showing increasing reliance on vestibular cues as stimulus amplitudes increased. VL subjects could not perform this reweighting, and their stimulus-response behavior remained quite linear. Transfer function curve fits based on a simple feedback control model provided estimates of postural stiffness, damping, and feedback time delay. There were only small changes in these parameters with increasing visual stimulus amplitude. However, stiffness increased as much as 60% with increasing support surface amplitude. To maintain postural stability and avoid resonant behavior, an increase in stiffness should be accompanied by a corresponding increase in damping. Increased damping was achieved primarily by decreasing the apparent time delay of feedback control rather than by changing the damping coefficient (i.e., corrective torque related to body-sway velocity). In normal subjects, stiffness and damping were highly correlated with body mass and moment of inertia, with stiffness always about 1/3 larger than necessary to resist the destabilizing torque due to gravity. The stiffness parameter in some VL subjects was larger compared with normal subjects, suggesting that they may use increased stiffness to help compensate for their loss. Overall results show that the simple act of standing quietly depends on a remarkably complex sensorimotor control system.

Sensorimotor integration in human postural control

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Biomechanics And Motor Control Of Human Movement

The purpose of this perspective article is to describe the use of a physiological profile approach to falls risk assessment and prevention that has been developed by the Falls and Balance Research Group of the Prince of Wales Medical Research Institute, Sydney, Australia. The profile's use for people with a variety of factors that put them at risk for falls is discussed. The Physiological Profile Assessment (PPA) involves a series of simple tests of vision, peripheral sensation, muscle force, reaction time, and postural sway. The tests can be administered quickly, and all equipment needed is portable. The results can be used to differentiate people who are at risk for falls ("fallers") from people who are not at risk for falls ("nonfallers"). A computer program using data from the PPA can be used to assess an individual's performance in relation to a normative database so that deficits can be targeted for intervention. The PPA provides valid and reliable measurements that can be used for assessing falls risk and evaluating the effectiveness of interventions and is suitable for use in a range of physical therapy and health care settings.

/pdf/a-physiological-profile-approach-to-falls-risk-assessment-o0zjoaylyk.pdf

A Physiological Profile Approach to Falls Risk Assessment and Prevention

Skilled motor behaviour, from the graceful leap of a ballerina to a precise pitch by a baseball player, appears effortless but reflects an intimate interaction between the complex mechanical properties of the body and control by a highly distributed circuit in the CNS An important challenge for understanding motor function is to connect these three levels of the motor system — motor behaviour, limb mechanics and neural control Optimal feedback control theory might provide the important link across these levels of the motor system and help to unravel how the primary motor cortex and other regions of the brain plan and control movement

/pdf/optimal-feedback-control-and-the-neural-basis-of-volitional-2ypl1d3rcs.pdf

Optimal feedback control and the neural basis of volitional motor control

Touch and pressure stimulation of the body surface can strongly influence apparent body orientation, as well as the maintenance of upright posture during quiet stance. In the present study, we investigated the relationship between postural sway and contact forces at the fingertip while subjects touched a rigid metal bar. Subjects were tested in the tandem Romberg stance with eyes open or closed under three conditions of fingertip contact: no contact, touch contact (< 0.98 N of force), and force contact (as much force as desired). Touch contact was as effective as force contact or sight of the surroundings in reducing postural sway when compared to the no contact, eyes closed condition. Body sway and fingertip forces were essentially in phase with force contact, suggesting that fingertip contact forces are physically counteracting body sway. Time delays between body sway and fingertip forces were much larger with light touch contact, suggesting that the fingertip is providing information that allows anticipatory innervation of musculature to reduce body sway. The results are related to observations on precision grip as well as the somatosensory, proprioceptive, and motor mechanisms involved in the reduction of body sway.

https://link.springer.com/content/pdf/10.1007/BF00229188.pdf

Fingertip contact influences human postural control

Multisensory fusion: simultaneous re-weighting of vision and touch for the control of human posture.

The dynamics of pattern formation and change are studied in a complex multicomponent system, specifically the arms and legs of human Ss. Among the novel features observed are differential stability of coordinative modes produced by limbs moving in the same versus different directions (Experiment 1); transitions between coordinative modes preceded by a slow drift in relative phase (Experiments 1 and 2); bifurcations or phase transitions from 1 four-limb pattern to another (Experiment 2); and spontaneous emergence of non-1:1-frequency- and phase-locked patterns, in addition to periods of relative coordination (Experiment 3). All observed relative phasing patterns and their dynamics (stability, loss of stability, intermittency) are shown to arise from the same underlying nonlinear dynamical structure, an important feature of which is broken symmetry.

Symmetry breaking dynamics of human multilimb coordination.

The problem of how the nervous system fuses sensory information from multiple modalities for upright stance control remains largely unsolved. It is well established that the visual, vestibular, and...

Controlling human upright posture: velocity information is more accurate than position or acceleration.

This study tested the hypotheses that all major joints along the longitudinal axis of the body are equally active during quiet standing and that their motions are coordinated to stabilize the spatial positions of the center of mass (CM) and head. Analyses of the effect of joint configuration variance on the stability of the CM and head positions were performed using the uncontrolled manifold (UCM) approach. Subjects stood quietly with arms folded across their chests for three 5-min trials each with and without vision. The UCM analysis revealed that the six joints examined were coordinated such that their combined variance had minimal effect on the CM and head positions. Removing vision led to a structuring of the resulting increased joint variance such that little of the increase affected stability of the CM and head positions. The results reveal a control strategy involving coordinated variations of most major joints to stabilize variables important to postural control during quiet stance.

https://www.physiology.org/doi/pdf/10.1152/jn.01142.2006

John J. Jeka

Papers

Fingertip contact influences human postural control

Multisensory fusion: simultaneous re-weighting of vision and touch for the control of human posture.

Symmetry breaking dynamics of human multilimb coordination.

Controlling human upright posture: velocity information is more accurate than position or acceleration.

Control and estimation of posture during quiet stance depends on multijoint coordination.