Emergence of Lissajous Patterns as a Function of a Perturbation Frequency in Postural Responses to the Short Sinusoidal Translations of Varying Frequencies.

The existence of in-phase and anti-phase postural responses to sinusoidal perturbations to the base of support is well known. In this study, we investigate if such coordinated postural responses exist at 'near-sway' perturbations where the perturbation amplitudes are kept within the range of normal sway lengths in healthy adults (n=10). The postural responses are analyzed via bursts of anterior-posterior (AP) 2.

Using multiple placements of accelerometers to measure cardiovascular pulse transit times.

To measure pulse transit times (PTT) and calculate pulse wave velocities (PWV), tri-axial and uniaxial accelerometers were placed in groups of 2 to 4 over the manubrium, xiphoid process, forehead, wrist and ankle, and/or over the carotid, femoral, and posterior auricular arteries in 11 consented supine subjects. Signals were sampled at 1 kHz and filtered. Radial vectors were calculated from the tri-axial measurements.

Using fuzzy logic in psychophysical experiments to separate hits, false positives and guesses in posturally perturbed standing subjects.

In a 2-Alternative Forced Choice Interval task (2AFCi), a standing subject is required to press a button once or twice to signal in which of two 4 s sequential intervals that (s)he thought that a short ≤ 16 mm postural perturbation had occurred. The perturbation might or might not result in transient changes of the subject's Anterior-Posterior Center of Pressure (APCOP) or in other measures. This paper used fuzzy inference to explore whether the correctness of a subject's stimulus detection can be gleaned from analyzing changes in one of more metrics related to changes in the APCOP.

Dependence of elbow joint stiffness measurements on speed, angle, and muscle contraction level.

Elbow joint stiffness is critical to positioning the hand. Abnormal elbow joint stiffness may affect a person's ability to participate in activities of daily living. In this work, elbow joint stiffness was measured in ten healthy young adults with a device adapted from one previously used to measure stiffness in other joints.

Psychophysical detection thresholds in anterior horizontal translations of seated and standing blindfolded subjects.

To help separate out the contributions of the somatosensory and vestibular systems to postural and sway control, short (1, 4 and 16 mm) anterior translations of lengths less than the normal sway path length were made of a platform upon which blindfolded young adult test subjects (n=12) stood or sat. Acceleration detection thresholds from these short moves were compared in standing vs seated conditions using a 2-Alternative [Interval] Forced-Choice psychophysical test protocol. A negative power law trading relationship was found between peak acceleration threshold and move length and duration for standing subjects.

Categorizing and comparing psychophysical detection strategies based on biomechanical responses to short postural perturbations.

Background: A fundamental unsolved problem in psychophysical detection experiments is in discriminating guesses from the correct responses. This paper proposes a coherent solution to this problem by presenting a novel classification method that compares biomechanical and psychological responses.

Methods: Subjects (13) stood on a platform that was translated anteriorly 16 mm to find psychophysical detection thresholds through a Adaptive 2-Alternative-Forced-Choice (2AFC) task repeated over 30 separate sequential trials.

The effects of diabetes and/or peripheral neuropathy in detecting short postural perturbations in mature adults.

Background: This study explored the effects of diabetes mellitus (DM) and peripheral neuropathy (PN) on the ability to detect near-threshold postural perturbations.

Methods: 83 subjects participated; 32 with type II DM (25 with PN and 7 without PN), 19 with PN without DM, and 32 without DM or PN. Peak acceleration thresholds for detecting anterior platform translations of 1 mm, 4 mm, and 16 mm displacements were determined.

A phase-locked loop model of the response of the postural control system to periodic platform motion.

A phase-locked loop (PLL) model of the response of the postural control system to periodic platform motion is proposed. The PLL model is based on the hypothesis that quiet standing (QS) postural sway can be characterized as a weak sinusoidal oscillation corrupted with noise. Because the signal to noise ratio is quite low, the characteristics of the QS oscillator are not measured directly from the QS sway, instead they are inferred from the response of the oscillator to periodic motion of the platform.

A quiet standing index for testing the postural sway of healthy and diabetic adults across a range of ages.

A quiet standing index is developed for tracking the postural sway of healthy and diabetic adults over a range of ages. Several postural sway features are combined into a single composite feature C that increases with age a. Sway features are ranked based on the r(2)-values of their linear regression models, and the composite feature is a weighted sum of selected sway features with optimal weighting coefficients determined using principal component analysis.

Assessing the psychophysics of posture control and its physiological correlates.

Graphical visualization methods are described that enable psychophysical detection data to be quantitatively correlated with underlying physiological data in postural control studies. Stitched, raster and ensemble averaged time-series plots are graphical tools that can guide later quantitative analysis. The examples presented point out the role that early Tibialis Anterior and later Gastrocnemius EMG activation might play in the 2-Alternative Forced Choice psychophysical detection of 16 mm horizontal anterior perturbations of a sliding platform on which a subject stands, and their linkage to AP and ML Center of Pressure changes brought about by a perturbation.

Amplitude demodulation of entrained sway to analyze human postural control.

This paper presents an innovative technique to study postural control. Our translating platform, the Sliding Linear Investigative Platform For Analyzing Lower Limb Stability and Simultaneous Tracking, EMG and Pressure mapping (SLIP-FALLS-STEPm), makes precise, vibration movements under controlled conditions. We look at the psychophysical thresholds to the perception of a sinusoidally induced sway.

A biomechanical model of human ankle angle changes arising from short peri-threshold anterior translations of platform on which a subject stands.

This study modeled ankle angle changes during small forward perturbations of a standing platform. A two-dimensional biomechanical inverted pendulum model was developed that uses sway frequencies derived from quiet standing observations on a subject's Anterior Posterior Center of Pressure (APCoP) to track ankle angle changes during a 16 mm anterior displacement perturbation of a platform on which a subject stood. This model used the total torque generated at the ankle joint as one of the inputs, and calculated it assuming a PID controller.

Design and characterization of a nano-encapsulated self-referenced fluorescent nitric oxide sensor for wide-field optical imaging.

A nano-encapsulated fluorescence dye DAF-2 sensor that is specifically sensitive to nitric oxide (NO) was fabricated by using an electrostatic layer-by-layer (LbL) self-assembly technique. Fluorescence calibrations of the NO sensor were collected by a wide-field optical imaging system and a fluorescence spectrometer using NO standards generated by the self decomposition of S-nitrosol-acetyl-penicillamine (SNAP). The NO sensor consists of two fluorescence dyes, indicator DAF-2 and a reference R-PE.

A system for measurement and calibration of nonorthogonal joints and limbs in humans.

Human limbs are a multilinked system in which the revolute joints are not orthogonal to the limb segments or to each other. The standard method for movements of multilinked systems is the Denavit-Hartenberg (DH) representation, which is useful for orthogonal systems. When applied to non-orthogonal systems, the DH representation projects the reference frames outside of the limb segments.

Analyses of rotational singularities in ferret visual cortex.

Activity maps of spatial orientation, obtained by intrinsic optical imaging of the mammalian visual cortex, show the formation of pinwheel-like structures that rotate either clockwise or counterclockwise around zero dimensional points called singularities. Any research that is oriented towards exploring the formation and physiological role of these singularities during an experiment requires an automated tool that can rapidly identify the location of these singularities. In this work we have developed such a tool that looks for the existence of singularities for a certain radius at every pixel location in the angle map.

Effects of diabetic neuropathy on body sway and slip perturbation detection in older population.

Postural control is a common mechanism to compensate for unexpected displacements of the body. In the older population, a slip or fall due to a failure of postural control is a common cause of morbidity and mortality. The ability of postural control decreases with aging or neuropathy.

Effect of lateral perturbations on psychophysical acceleration detection thresholds.

Background: In understanding how the human body perceives and responds to small slip-like motions, information on how one senses the slip is essential. The effect of aging and plantar sensory loss on detection of a slip can also be studied. Using psychophysical procedures, acceleration detection thresholds of small lateral whole-body perturbations were measured for healthy young adults (HYA), healthy older adults (HOA) and older adults with diabetic neuropathy (DOA).

Postural control and detection of slip/fall initiation in the elderly population.

One of the common causes of morbidity and mortality in workplaces is related to slips or falls. Reaction to external disturbances, such as slips or falls, requires a process of perturbation detection and control of motion changes. Postural control is a common mechanism to compensate unexpected displacements of the body.

A comparative study of reaction times between type II diabetics and non-diabetics.

Background: Aging has been shown to slow reflexes and increase reaction time to varied stimuli. However, the effect of Type II diabetes on these same reaction times has not been reported. Diabetes affects peripheral nerves in the somatosensory and auditory system, slows psychomotor responses, and has cognitive effects on those individuals without proper metabolic control, all of which may affect reaction times.

Multi-joint movement of the cat hindlimb evoked by microstimulation of the lumbosacral spinal cord.

Microstimulation of the lumbosacral spinal cord may be an effective tool for the restoration of locomotion after spinal cord injury. To examine this possibility, complex coordinated multi-joint hindlimb movements were evoked by electrical stimulation with sine waveform modulation using a single microelectrode positioned in the L5-S1 spinal cord. Four types of hindlimb movement (flexion, extension, abduction, and adduction) were identified, and their stimulation locations were mapped onto cross-sectional drawings of L5-S1 spinal cord following histological examination of electrode tracks in the cord.

Treatment of Spasticity in Spinal Cord Injury with Dronabinol, a Tetrahydrocannabinol Derivative.

Spinal-cord-injured patients and the medical literature have increasingly reported anecdotes regarding tetrahydrocannabinol (THC)-induced spasmolysis. These reports motivated this trial of dronabinol, a THC derivative, for the treatment of spasticity in the spinal-cord-injured population. Five made quadriplegic patients were given oral dronabinol in escalating doses from 5 mg BID to 20 mg TID in addition to their current, but ineffective, spasmolytic regime.