Biomedical subjects

Robert A Scheidt

Publications and source records attributed to Robert A Scheidt.

5 recordsLinked to original sources

PubMed2006

Neural and electromyographic correlates of wrist posture control.

In identical experiments in and out of a MR scanner, we recorded functional magnetic resonance imaging and electromyographic correlates of wrist stabilization against constant and time-varying mechanical perturbations. Positioning errors were greatest while stabilizing random torques. Wrist muscle activity lagged changes in joint angular velocity at latencies suggesting trans-cortical reflex action. Drift in stabilized hand positions gave rise to frequent, accurately directed, corrective movements, suggesting that the brain maintains separate representations of desired wrist angle for feedback control of posture and the generation of discrete corrections. Two patterns of neural activity were evident in the blood-oxygenation-level-dependent (BOLD) time series obtained during stabilization. A cerebello-thalamo-cortical network showed significant activity whenever position errors were present. Here, changes in activation correlated with moment-by-moment changes in position errors (not force), implicating this network in the feedback control of hand position. A second network, showing elevated activity during stabilization whether errors were present or not, included prefrontal cortex, rostral dorsal premotor and supplementary motor area cortices, and inferior aspects of parietal cortex. BOLD activation in some of these regions correlated with positioning errors integrated over a longer time-frame consistent with optimization of feedback performance via adjustment of the behavioral goal (feedback setpoint) and the planning and execution of internally generated motor actions. The finding that nonoverlapping networks demonstrate differential sensitivity to kinematic performance errors over different time scales supports the hypothesis that in stabilizing the hand, the brain recruits distinct neural systems for feedback control of limb position and for evaluation/adjustment of controller parameters in response to persistent errors.

Adult↗

PubMed2005

Remapping hand movements in a novel geometrical environment.

The issue of how the Euclidean properties of space are represented in the nervous system is a main focus in the study of visual perception, but is equally relevant to motor learning. The goal of our experiments was to investigate how the properties of space guide the remapping of motor coordination. Subjects wore an instrumented data glove that recorded the finger motions. Signals generated by the glove operated a remotely controlled endpoint: a cursor on a computer monitor. The subjects were instructed to execute movements of this endpoint with controlled motions of the fingers. This required inverting a highly redundant map from fingers to cursor motions. We found that 1) after training with visual feedback of the final error (but not of the ongoing cursor motion), subjects learned to map cursor locations into configurations of the fingers; 2) extended practice of movement led to more rectilinear cursor movement, a trend facilitated by training under continuous visual feedback of cursor motions; 3) with practice, subjects reduced motion in the degrees of freedom that did not contribute to the movements of the cursor; 4) with practice, subjects reduced variability of both cursor and hand movements; and 5) the reduction of errors and the increase in linearity generalized beyond the set of movements used for training. These findings suggest that subjects not only learned to produce novel coordinated movement to control the placement of the cursor, but they also developed a representation of the Euclidean space on which hand movements were remapped.

Analysis of Variance↗

PubMed2005

Interaction of visual and proprioceptive feedback during adaptation of human reaching movements.

People tend to make straight and smooth hand movements when reaching for an object. These trajectory features are resistant to perturbation, and both proprioceptive as well as visual feedback may guide the adaptive updating of motor commands enforcing this regularity. How is information from the two senses combined to generate a coherent internal representation of how the arm moves? Here we show that eliminating visual feedback of hand-path deviations from the straight-line reach (constraining visual feedback of motion within a virtual, "visual channel") prevents compensation of initial direction errors induced by perturbations. Because adaptive reduction in direction errors occurred with proprioception alone, proprioceptive and visual information are not combined in this reaching task using a fixed, linear weighting scheme as reported for static tasks not requiring arm motion. A computer model can explain these findings, assuming that proprioceptive estimates of initial limb posture are used to select motor commands for a desired reach and visual feedback of hand-path errors brings proprioceptive estimates into registration with a visuocentric representation of limb position relative to its target. Simulations demonstrate that initial configuration estimation errors lead to movement direction errors as observed experimentally. Registration improves movement accuracy when veridical visual feedback is provided but is not invoked when hand-path errors are eliminated. However, the visual channel did not exclude adjustment of terminal movement features maximizing hand-path smoothness. Thus visual and proprioceptive feedback may be combined in fundamentally different ways during trajectory control and final position regulation of reaching movements.

Adaptation, Physiological↗

PubMed2005

A physiologically based clinical measure for spastic reflexes in spinal cord injury.

OBJECTIVE: To test the validity of the Spinal Cord Assessment Tool for Spastic reflexes (SCATS), a clinical tool intended to rate spastic motor behavior after spinal cord injury (SCI). DESIGN: By using correlational analyses, the SCATS was validated using concurrent measurements of kinematics and electromyograms and traditional assessments of spasms and spastic hypertonia. SETTING: Research laboratory (kinematics and electromyography) and outpatient medical clinic (traditional measures of spastic hypertonia). PARTICIPANTS: Eleven people with SCI were used for kinematic and electromyographic measurements. Seventeen people with SCI were used for comparison with other clinical scales. INTERVENTIONS: Not applicable. Main outcome measures Kinematic and surface electromyographic measurements of the tested lower extremity were used to quantify magnitude and/or duration of motor behaviors, and the Penn Spasm Frequency Scale (PSFS) and the Ashworth Scale were used to measure spasm frequency and resistance to joint movement for the hip flexors, knee flexors, and ankle plantarflexors, respectively. Concurrently, the SCATS was used to assess the clonus response to an imposed ankle dorsiflexion, the flexion response to a stimulus to the foot, and the knee extensor activity in response to an imposed leg extension. Each component of the SCATS was compared with the Ashworth Scale, the PSFS, and kinematic and electromyographic measurements by using the Spearman rank correlation test. RESULTS: Clonus, flexor spasm, and extensor spasm responses measured by using the SCATS correlated significantly with kinematic and electromyographic recordings (P<.01). Significant correlations were also observed between the SCATS extensor spasms and the Ashworth scores for hip and knee flexors and for ankle plantarflexors (rho=.98, .88, .61, respectively). Also, SCATS flexor spasms and SCATS clonus scores correlated significantly with some of the Ashworth scores. Only SCATS clonus scores correlated significantly with spasm frequency measures (rho=.59, P<.05). CONCLUSIONS: The SCATS produced a valid measure of 3 distinct types of spastic motor behaviors in SCI and may provide a complementary tool for measuring spastic hypertonia. Such a measure is valuable because current assessment tools do not differentiate between the different types of spastic motor behaviors that manifest after SCI. Distinguishing the 3 spastic reactions using an efficient and valid clinical tool may help guide management of spastic hypertonia in SCI.

Adolescent↗

PubMed2004

Computerized biofeedback knee goniometer: acceptance and effect on exercise behavior in post-total knee arthroplasty rehabilitation.

OBJECTIVE: To assess device accuracy, patient acceptance, and effect of a computerized biofeedback knee goniometer (CBG), on patients' compliance with active range of motion (AROM) exercises after total knee arthroplasty (TKA). DESIGN: Two-stage study: measurement validation on asymptomatic controls and an unblinded, multiple crossover trial. SETTING: Inpatient rehabilitation. PARTICIPANTS: Asymptomatic controls (n=14) and post-TKA inpatients (n=11). INTERVENTIONS: For measurement validation, CBG-angle measurements were compared with manual, clinician-obtained angles. To assess motivational effect, the CBG was worn after TKA; on alternating days, it either monitored AROM silently (no feedback) or provided audiovisual feedback about reaching preset range of motion (ROM) goals and prompted the patients to exercise when idle. MAIN OUTCOME MEASURES: To assess accuracy, the device's readings were compared with manual measurements. Patient satisfaction was determined by a self-report questionnaire; exercise compliance was assessed by calculating activity rate and stratified interactivity intervals. RESULTS: CBG readings reproduced clinician measurements reliably between 0 degrees and 100 degrees (eta(2)=98.5%). Auditory feedback was more helpful than visual feedback for motivating exercise. During feedback-on days, the mean total activity rate +/- standard deviation was 15.1+/-10.9 activity counts per hour, and the interactivity interval was 6.7+/-5.7 minutes. The activity rate was higher on feedback-off days-22.5+/-11.1 counts/hour (P=.11)-and the mean interactivity interval was 3.6+/-2.7 minutes (P=.07). CONCLUSIONS: The CBG provided reliable, unbiased estimates of clinician measurements of joint angle within the range of 0 degrees to 100 degrees. The CBG was accepted well by most patients. Surprisingly, slightly more ROM activity was noted during feedback-off days than feedback-on days.

Analysis of Variance↗