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Biomedical subjects

J F Soechting

Publications and source records attributed to J F Soechting.

89 records · Page 5Linked to original sources
PubMed1978

Response to transient disturbances during intentional forearm flexion in man.

Steps of torque were applied to the human forearm during intentional flexion movements with peak velocities of 40-500 degrees/sec and during ballistically initiated flexion movements. The question asked was whether or not the motor ouput to both agonist and antagonist muscles is independent of sensory input data or is accessible and influenced by these inputs. The data obtained demonstrate unequivocally that the applied perturbation affects the motor output, irrespective of the speed of the movement. The time of onset of the reflex changes in motor output and their maxima are related to the movement's parameters. Data are presented which indicate that the source for the reflex changes observed are the muscle spindles.

Afferent Pathways↗
PubMed1977

Dynamic relations between natural vestibular inputs and activity of forelimb extensor muscles in the decerebrate cat. I. Motor output during sinusoidal linear accelerations.

Decerebrate cats were subjected to sinusoidal linear accelerations along the animal's horizontal and vertical axes, while recording the EMG activity of both triceps brachii muscles. This activity was found to be sinusoidally modulated in response to the accelerations and thus phase and gain relations between motor output and input acceleration could be obtained. They were found to be the same for accelerations along each of the three axes. In particular the gain dropped by 14-20 dB over a frequency range from 0.2 to 1.0 Hz and the phase of the motor output showed a lag of 40-60 degrees at 1.0 Hz. Thus, it was concluded that (1) the dynamic behavior of utricular and saccular receptors is the same, (2) the changes in motor activity observed during accelerations along the vertical axis are mostly due to the activation of saccular afferents, and (3) the motor output cannot simply result from vestibular afferent activities being relayed directly to the spinal motoneurons via the vestibulo-spinal tracts.

Acceleration↗
PubMed1977

Dynamic relations between natural vestibular inputs and activity of forelimb extensor muscles in the decerebrate cat. II. motor output during rotations in the horizontal plane.

Decerebrate cats with the spinal cord sectioned at low thoracic levels were submitted to rotations in the horizontal plane. The position of the animal with respect to the axis of rotation was such that horizontal canal afferents were activated either alone or in combination with macular afferents. The EMG activity from the triceps brachii muscles of both forelimbs was recorded. The main findings were as follows. (1) The motor output to each forelimb extensor is increased by an increase in the activity of the horizontal canal afferents from the contralateral labyrinth. The phase of the motor output with respect to that of the vestibular afferents shows a lag which increases with frequency, reaching about 85 degrees at 1.0 Hz. (2) The macular and horizontal canal inputs are independently processed in the central nervous system and the motor output in response to both inputs applied simultaneously is a linear summation of the outputs expected for each of the inputs.

Acceleration↗
PubMed1977

Dynamic relations between natural vestibular inputs and activity of forelimb extensor muscles in the decerebrate cat. III. Motor output during rotations in the vertical plane.

Decerebrate cats with the spinal cord sectioned at low thoracic levels were subjected to sinusoidal rotations in the vertical plane, while recording the EMG activity of both triceps brachii muscles. The applied stimulus activated utricular and saccular receptors as well as the vertical semicircular canals. Using results presented in preceding papers 2,3, namely the dynamic response characteristics of the motor output to macular inputs and the fact that the responses to otolith and canal stimulation summate linearly 3, it is deduced that the dynamic characteristics of the motor output in response to stimulation of the vertical canals are the same as those to horizontal canal stimulation. The implication of these findings vis-à-vis the problem of central processing of vestibular inputs and the problem of postural stability is discussed.

Acceleration↗
PubMed1976

Changes in a motor pattern following cerebellar and olivary lesions in the squirrel monkey.

Squirrel monkeys were trained to perform ballistically initiated flexion movements of the forearm. It is shown that the motor output to agonist and antagonist subsequent to the onset of the movement depends continuously on the movement's parameters, primarily the velocity, as in man. The contribution of cerebellar activities to maintain this relationship was investigated by means of discrete lesions of the cerebellum and inferior olive. After lesions of the cerebellar nuclei, EMG activity of agonist and antagonist is no longer precisely structured. This result implies that activity of the cerebellar nuclei is necessary to maintain the gain and timing of the relationship between sensory inputs and motor outputs. Participation of the inferior olive is also required, since lesions of this structure mimic the effect of destruction of the cerebellar nuclei. Lesions of the cerebellar cortex, instead, affect mainly the timing of the motor output.

Animals↗
PubMed1976

Transfer characteristics between EMG activity and muscle tension under isometric conditions in man.

The relationship between motor unit activity and a voluntarily produced, sinusoidally modulated isometric tension was evaluated as a function of the modulation frequency. These date are reported in terms of the gain and phase difference of the motor activity (input) and tension (output) relationship, the gain being the logarithmic ratio of the amplitudes of the output and input sinusoids. It was found that an increase in the modulation amplitude of the motor unit activity was required to produce the same amount of modulation of the output tension as the modulation frequency was increased. For example, the modulation amplitude of the activity is about twice as much at 2 Hz as at 0.25 Hz and about 4 times as much at 5 Hz. It was also found that the maximum tension which could be produced voluntarily during brief jerks at 5 Hz was the same as the maximum sustained tension which could be attained. This latter finding emphasizes the importance of recruitment and especially synchronization of motor unit activity to the gradation of output tension.

Action Potentials↗
PubMed1976

Influence of mechanical properties on the relation between EMG activity and torque.

An attempt was made to determine the average stiffness and viscosity of the muscle groups responsible, in human subjects, for the flexion and extension of the forearm, when these movements are produced intentionally. To this end, the subjects were instructed to produce sinusoidal movements by tracking acoustic and visual signals. 1. By recording simultaneously the sinusoidal angular variations and the EMG activity of both triceps and biceps it was possible to determine the phase angle between EMG and inertial torque at different frequencies (between 0.2 and 5 Hz). 2. The known phase relations between EMG and torque were then subtracted from this plot obtaining, therefore, the phase characteristics of the mechanical system (forearm-lever complex). 3. The average resonant frequency for different amounts of intentional contraction of the muscles responsible for the motion was 0.8 Hz, leading to an estimate of the average stiffness of 2.57 kgw.m/rad. 4. The slope of the phase in proximity of the resonant frequency lends an estimate for the viscosity of 0.85 kgw.m.sec/rad. 5. The contribution to the motion by elastic forces and the active contraction due to intentional motor commands was also considered.

Arm↗