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Biomedical subjects

G L Gottlieb

Publications and source records attributed to G L Gottlieb.

At least 73 records · Page 4Linked to original sources
PubMed1988

Practice improves even the simplest movements.

Three subjects practiced accurate, fast elbow flexions of 54 degrees to a 3 degrees wide target. Movements of 36 degrees, 54 degrees and 72 degrees were then tested. Comparison over the three distances showed that the normally monotonic relationship between movement distance and movement time is alterable by specific training. Subjects learn to go faster over the practiced distance by refining their neural commands to the muscles. The benefits of practice only partially transfer to other distances. We conclude that many of the relationships seen among movement variables in simple tasks are plastic in nature and affected by prior experience.

Adult↗
PubMed1988

Accuracy constraints upon rapid elbow movements.

Kinematic and myoelectric variables associated with rapid elbow-flexion movements of various distances to targets of various widths were studied. The movement time in these experiments conformed to Fitts' law: movement time increased with target distance and decreased with target width. Peak movement velocity, electromyograph (EMG) duration, and EMG quantity were poorly described by Fitts' law, for increases in target width were accompanied by increases in these variables. We show with regression equations, using separate weighting coefficients, that kinematic and myoelectric variables can be related to distance and target width. The use of distance and target width as independent variables allows us to suggest that the literature does not agree on the relation between EMG and distance moved partly because of the influences of the target on this relationship. We propose that human voluntary movement involves a subject "strategy," or set of internal constraints, that affect movement outcome. Significant elements of this strategy, such as how accurately to perform the task, may not be recognized or controlled in many movement paradigms, in spite of uniform instruction to subjects and similar apparatus.

Journal Article↗
PubMed1988

Compliance of single joints: elastic and plastic characteristics.

1. Step changes in torque were applied to the elbow or ankle joint of normal human subjects who exerted constant levels of effort. They were instructed to not react to the torque but to allow their limbs to move to a new equilibrium position. In this experimental paradigm, the joint may be characterized by a nonlinear compliant element. The aim of this study was to characterize the elastic properties of the compliant element. 2. Joint elasticity is described by an S-shaped relation between torque and angle (a "compliant characteristic curve"). The stiffness of a joint is greatest for small perturbations and decreases as the size of the perturbation is increased whether the limb is loaded or unloaded from its initial equilibrium. 3. The S shape of the compliant characteristic curve is relatively constant when measured at different initial joint angles from the same initial joint torque. 4. Higher levels of initial muscle torque increase the steepness of the compliant characteristic curve. 5. All changes in initial joint torque and angle preserve the S shape. The inflection point of the characteristic curve is always at the initial equilibrium angle and torque. This shifting of the inflection point of the torque-angle relation implies a fundamental plasticity in joint compliance. The elastic component is not invariant but changes with the joint's initial equilibrium state. 6. Changes in muscle tension and length that result from a perturbation are accompanied by changes in muscle activation. The relationship between perturbation torque and mean equilibrium EMG is similar to that found for voluntary isometric contraction. It is not possible to conclude what proportion of the late EMG response to perturbation is mediated by segmental reflex mechanisms. 7. At the levels of torque used here, changes in joint stiffness are highly correlated with changes in tonic contraction of the muscle opposing the load. This change in stiffness is not the result of antagonist coactivation, which was minimal. 8. The compliant characteristic curves of elbow and ankle are qualitatively similar. The principal difference is due to the greater passive stiffness of the ankle. 9. Our findings are inconsistent with aspects of the theory of invariant characteristics or with models of movement and load compensation that postulate a control scheme based only on the setting of muscle and reflex equilibrium points. The data are also incompatible with models that only control the elastic stiffness of the muscle.

Ankle Joint↗
PubMed1988

Reliability of psychiatric scales in patients with dementia of the Alzheimer type.

For 43 patients with probable Alzheimer's disease who were screened for psychiatric disorders, the interrater reliability of the Global Deterioration Scale, BPRS, and Hamilton Rating Scale for Depression was high (intraclass correlation, 0.82-0.998). As expected, the prevalence of psychiatric symptoms in this sample was low. The score on the Zung Self-Rating Depression Scale correlated with the score on the rater-administered Hamilton depression scale in patients whose Alzheimer's disease was of low severity (N = 24) but not high severity (N = 19).

Aged↗
PubMed1986

Movement deficits caused by hyperexcitable stretch reflexes in spastic humans.

Spastic patients were instructed to make accurate, rapid ankle dorsiflexion and plantarflexion movements over different distances to a target. Ankle position and surface electromyograms (EMGs) from tibialis anterior (TA) and soleus (SOL) muscles were recorded. In 3 of 8 spastic patients tested, dorsiflexion evoked velocity-dependent activation of the antagonist (SOL) muscle which impeded the movement to the extent that the limb unintentionally reversed movement direction. We propose that this activation is reflex in origin since it is tightly synchronized, has a large peak amplitude, occurs about 50 ms after the initiation of the movement, and is velocity dependent. One of the 3 patients who had reflex-induced antagonist activation in dorsiflexion also demonstrated sustained clonus during plantarflexion. This usually occurred only if the target had been overshot so that the return of the limb stretched the soleus muscle and triggered clonus. We conclude that in some patients, hyperactive stretch reflexes cause movement deficits.

Adult↗
PubMed1986

Stretch reflexes of the normal infant.

Tendon-jerk reflexes were tested in normal, fullterm infants aged one to four days. EMGs were recorded from gastrocnemius-soleus and tibialis anterior muscles. Reflex-like EMGs were evoked when tapping sites which should not excite the muscles from which that activity is recorded--this included the simultaneous activation of antagonistic muscles by a tendon tap. The possible mechanisms which could produce these results are discussed, as are the possible relationships between the proposed pathways and the reciprocally excitatory paths in cerebral palsy.

Electromyography↗
PubMed1985

A note on accepting the null hypothesis: problems with respect to the mass-spring and pulse-step models of movement control.

Models are sometimes developed on the premise that there are no differences between two or more conditions regardless of experimental manipulation. This article argues that unless a very sensitive experiment (or series of experiments) was conducted, such conclusions are often premature. Design and statistical factors such as alpha level, variability, sample size, and treatment effect are all determinants of the sensitivity of the experiment. It is sometimes the case that an experiment produces differences between means and yet the null hypothesis is not rejected because of high variability within experimental conditions or because too few subjects were used. Unless the probability of detecting a difference between groups is known, it would seem unwise to conclude that no difference exists. Judgment on the model should be suspended. Examples are taken from the mass-spring and pulse-step models fro voluntary movement control to illustrate the problem.

Journal Article↗
PubMed1985

Evaluation of cervical stimulation for chronic treatment of spasticity.

Electrical stimulation of the spinal cord (SCS) to reduce spasticity was evaluated in seven patients who, along with their physicians, perceived significant and prompt benefit from stimulation. In two 24-hour test periods, on or off stimulation, we used two independent methods of evaluation: quantitative measures of joint compliance and stretch reflexes, and a standardized neurologic examination. Neither method did better than chance in determining whether SCS was actually being received. Problems with the experimental protocol are discussed, but the results cannot be interpreted as supporting the efficacy of SCS as a treatment for spasticity.

Cerebral Palsy↗
PubMed1984

Orientation-induced artifacts in the measurement of monosynaptic reflexes.

Hoffmann and tendon jerk reflexes were tested in human subjects at various orientations between vertical, prone and supine. The data suggest that artifacts due to movement of soft tissue may explain the current disagreement in the literature on otolithic influences on these reflexes.

Electromyography↗
PubMed1984

Time series modeling of neuromuscular system.

The dynamic response of the human ankle joint to a bandlimited random torque perturbation superimposed on a constant bias torque is observed in normal human subjects. The applied torque input, the joint angular rotation output, and the electromyographic activity using surface electrodes from the extensor and the flexor muscles of the ankle joint were recorded. Transfer function models using time series techniques were developed for the torque - angular rotation input-output pair and for the angular rotation - electromyographic activity input-output pair. A parameter constraining technique was applied to develop more reliable models. It is shown that the asymptotic behavior of the system must be taken into account during parameter optimization to develop better predictive models.

Ankle Joint↗
PubMed1984

Muscle spindle contributions to the stretch-evoked electromyogram: nerve block studies.

Application of external torque to cause joint rotation evokes electromyogram (EMG) activity in the stretched muscles. These responses were studied in the tibialis anterior (TA) and flexor carpi ulnaris (FCU) muscles of normal human subjects in conjunction with a nerve block procedure by a local anesthetic agent. In both muscles, differences were observed between the myotatic and postmyotatic portions of the evoked EMG response. During recovery from a complete nerve block, the late components of the EMG (postmyotatic and stabilizing responses) recovered to the preblock magnitude faster than the early components (myotatic and late myotatic responses). Following partial nerve block, the late EMG components were diminished to a lesser extent and recovered faster than the early EMG components. This study suggests that peripheral afferent inputs are obligatory for the myotatic and late myotatic EMG responses. The effects of peripheral afferent inputs on postmyotatic responses are to modulate these later responses. However, the absence of peripheral afferent inputs will not prevent or even delay postmyotatic responses.

Adult↗
PubMed1984

Mathematical modeling and simulation of the postural control loop--Part II.

The engineering analysis and modeling of the neuromuscular system is an exciting and challenging area of research where we may learn something about the principles of controlling large, complex systems. This review is limited to the most peripheral subsystem: the postural control loop. In the first part, we reviewed the input-output properties of the motoneuron pool, modeling of the motor unit action potential and analysis of the interference electromyographic activity. Also included were the engineering techniques to quantitatively study electromyographic activity and its relationship to muscle force. The second part of this review focuses on the biomechanical models of the muscle based on Hill's work as well as the modern sliding filament theory. This section will also include models of the proprioceptive receptors: the muscle spindle organ and the Golgi tendon organ. In the final paper we will discuss various models and simulations of the peripheral loop and their applications to study physiological system behavior such as tremor.

Action Potentials↗
PubMed1984

Mathematical modeling and simulation of the postural control loop. Part III.

The engineering analysis and modeling of the neuromuscular system is an exciting and challenging area of research where we may learn something about the principles of controlling large, complex systems. This review is limited to the most peripheral subsystem: the postural control loop. In the first part, we reviewed the input-output properties of the motoneuron pool, modeling of the motor unit action potential, and analysis of the interference electromyographic activity. Aslo included were the engineering techniques to quantitatively study electromyographic activity and its relationship to muscle force. The second part of this review focuses on the biomechanical models of the muscle based on Hill's work as well as the modern sliding filament theory. This section also includes models of the proprioceptive receptors: the muscle spindle organ and the Golgi tendon organ. In this final paper we discuss various models and simulations of the peripheral loop and their applications to study physiological system behavior such as tremor.

Afferent Pathways↗