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Biomedical subjects

F Lestienne

Publications and source records attributed to F Lestienne.

At least 37 records · Page 2Linked to original sources
PubMed1984

Behavior of preoculomotor burst neurons during eye-head coordination.

Single-unit recordings from the pontine reticular formation in four monkeys have shown the presence of two classes of short-lead burst neurons firing during coordinated eye-head movements. The activity of one class showed a correlation with the size of saccadic movements performed during head movements; the other showed a correlation between firing pattern and the combined eye-head movement. Anatomical reconstructions of the recording sites point to an intermingling of the two cell types.

Animals↗
PubMed1984

Gaze changing behaviour in head restrained monkey.

The electromyographic activity of neck muscles and head torque were recorded in the alert, head-fixed rhesus monkeys together with the horizontal component of eye movements during pursuit movements, scanning movement and vestibular stimulation in darkness. A strong correlation between head torque and the horizontal component of eye position was demonstrated during these three different experimental situations. These conjugate head and eye movements are accompanied by a specific change in the timing of neck neuromuscular activation.

Acoustic Stimulation↗
PubMed1983

The information transmitted at final position in visually triggered forearm movements.

Visually triggered forearm movements were analyzed by an Information Theory approach. Human subjects made smooth movements which were characterized by moderate speeds, ranging about 100 degrees per second, by continuity in the position and velocity traces, and attainment of final average EMG levels before completion of the movement. We calculated the information transmitted by final position, biceps EMG, triceps EMG, and the ratio of the EMGs. The results were: (1) The information transmitted by final joint angle increased with number of targets but gradually levelled off. The maximum value was slightly over 3 bits, corresponding to an equivalent number of less than nine independent arm positions for a single movement. (2) The information transmitted by the ratio of the EMGs exceeds that transmitted by the biceps or triceps alone. (3) A previous theoretical prediction based on a spring model (Sakitt, 1980a) gives a moderately good fit to the experimental EMG ratio as a function of final position over a large range of angles. Our results lend consistency to two ideas about the nature of visually triggered forearm movements. First, our finding about the EMG ratio suggests that the basic motor program for final position is probably in terms of relative allocation of innervations, rather than looking up individual values. Second, single movements of this kind transmit surprisingly little information. If this is the case, it suggests that very fine accuracy is not achieved by a single program but requires feedback in order to program and execute additional movement.

Forearm↗
PubMed1983

[Postural adjustments associated with voluntary mobilization of the arm in microgravity conditions].

Adaptation of posture and of postural adjustments involved in voluntary elevation of the arm was studied during a seven day spaceflight. Results show an important forward inclination of the body at beginning of the flight. After three days in flight the position of the body was similar to the terrestrial posture. Together with this inclination, a redistribution of the electromyographic activities between flexor and extensor muscles of the ankle was observed. Anticipatory postural adjustments were always present in microgravity. These results are interpreted on the basis of body scheme.

Arm↗
PubMed1981

Functional organization of the motor process underlying the transition from movement to posture.

In these experiments we studied the organization of the neural pattern of activity underlying the achievement and maintenance of final limb position. The examination of the alpha motoneuronal inputs to flexors and extensors acting on the elbow and wrist joints revealed that a change from one posture to another required a modulation of both flexors and extensors. For a given position, the final EMG level of flexors and extensors is more variable than the ratio between the alpha neuronal activity of these two antagonistic muscles. Further, the ratio was not significantly affected by the direction, amplitude or velocity of the movement. These results indicate that the final position could be coded in the central nervous system (CNS) as the ratio of activity in antagonistic muscles acting on a joint.

Adult↗
PubMed1979

[Organization of reflex responses elicited in man by muscle stretch applied to uni- and bi-functional muscles].

The organization of human forearm reflexes following the application of extension torque perturbations has been studied in three flexors of the elbow: brachioradialis (BR), biceps (B), and pronator teres (PT). Two of these flexors are also involved in wrist supination: (B) and pronation (PT). During the perturbation, the wrist was fixed at various angles: from full supination to full pronation. The results show that the amplitude of the reflex responses of B and PT is highly dependent on wrist position. By eliminating biceps length changes as a source of observed reflex variation, it has been shown that the normalized reflex amplitude of B increases by 300% when the wrist position is varied from full pronation to full supination. In contrast, the BR muscle has a reflex response which is independent of wrist position. These results are discussed in relation to the role of reciprocal innervation and the possible action of receptors encoding wrist angle.

Humans↗
PubMed1979

Effects of inertial load and velocity on the braking process of voluntary limb movements.

The aim of this study has been to identify, in humans, the braking process underlying voluntary forearm movements performed at various velocities and amplitudes and against differential inertial loads. The procedure used to estimate the parameters of the braking process involved kinematic analysis of the movement and measurement of alpha-motoneural input to flexor and extensor muscles by recording electromyographic (EMG) activity. We have shown that when the agonist force does not exceed the passive viscoelastic tension developed by the extensor and flexor muscles, the movement can be braked by the viscoelastic forces alone. In contrast, above this force threshold, it was found that the motor output in agonist and antagonist muscles consists of well defined bursts of EMG activity, first in agonist then in antagonist muscles. The timing of these two bursts (duration of the agonist activity and onset of the antagonist activity) are clearly correlated with the value of the peak velocity. For the same peak velocity, the addition of inertial loads increase the excitation level of both agonist and antagonist muscles but does not change the timing of the EMG bursts. The discussion of these results focuses on the concept of "unit of movement" organized to reduce the large number of possible patterns of activation of the muscles acting on the same joint.

Biomechanical Phenomena↗
PubMed1977

[Modes of influence of vision on postural reactions associated with voluntary arm movements].

Postural changes associated with voluntary movements of the arm as observed during a positioning task, were studied on subjects standing upright on a force platform. Subjects performed the movements with either a normal visual field or without peripheral vision (tubular vision). Data analysis comprised the EMG activity of soleus and tibialis anterior and the displacement of the vertical component of the force applied to the platform. Average data of EMG indicate that the masking of the extrofoveal receptors increases the desactivation of soleus before the onset of the movement and provokes a burst of activity in the soleus 80 to 100 ms after the onset of the movement.

Action Potentials↗
PubMed1977

The stability of synergy in agonists during the execution of a simple voluntary movement.

The characteristics of muscular synergy between the main elbow flexors (biceps brachii, brachialis, brachoradialis were considered. The activities of these different muscles were recorded simultaneously with surface and wire electrodes. A quantitative analysis of the activity of each of these muscles and of their excitation levels was carried out during movements performed at various velocities and against different inertias. It was shown that: (1) the onset as well as the cessation of activity in the different muscles occur practically simultaneously and independently of the velocity and inertia of the movement; (2) the well-known linear relation between the integrated EMG of biceps brachii and the work can be extended to the other main flexors. This implies that the relation between the activities of the main flexors remains constant whatever the velocity and inertia may be. These results confirm the notion of 'Flexor Equivalent'. They also demonstrate a stability of the synergy between agonist muscles which must be distinguished particularly from the synergy between agonists and antagonists.

Adult↗