Biomedical subjects

B N Smetanin

Publications and source records attributed to B N Smetanin.

At least 19 recordsLinked to original sources

PubMed1999

Postural responses to combined vestibular and hip proprioceptive stimulation in man.

Vestibular-proprioceptive interaction in human postural control in the frontal plane was studied by analysing the lateral body sway evoked in a standing subject by a weak, near-threshold galvanic vestibular stimulation combined with a balanced, bilateral vibration of the medial gluteus muscles. The intensities of the stimuli were adjusted so that none of them produced a consistent postural response when delivered alone. The pattern of the lateral body sway evoked by the combined stimulation was compared with postural responses to suprathreshold vestibular stimulation and asymmetric (unilateral) vibration of the hip abductors. During the vestibular stimulation alone the head movement started earlier and was larger than movement of the hip. During unilateral vibration the head movement was delayed with respect to the hip movement and the amplitude of head deviation was less than that of the hip. The pattern of postural response to combined vestibular stimulation and balanced vibration resembled that observed under unbalanced, unilateral vibration in terms of both the latencies and amplitudes of deviation of the body segments from their respective baseline positions. It is suggested that the asymmetric vestibular signal provided by galvanic stimulation of the labyrinth introduces a bias into the reference frame for central interpretation of proprioceptive signals so that a symmetric proprioceptive input gives rise to a lateral body sway when referenced to an asymmetric vestibular input.

Adult↗

PubMed1999

[Errors in pointing under various body orientation relative to the gravity vector].

Errors in pointing to remembered target locations were measured in healthy subjects in upright, supine and prone positions, i.e. in three positions differing in body and arm movement orientation relative to the gravity vector. The X-error was unaffected by the body position, whereas the Y-error was dependent on subject's orientation relative to the gravity vector. In two lying positions, the subjects pointed below and in the vertical posture above the remembered target locations. On the contrary, the variable error was differentially affected by orientation of the movement trajectory relative to the gravity vector. In the supine position, the variable error was larger and in the prone position, smaller than in the upright posture. The gravity bias in pointing errors suggests that the motor program generated in the lying position is not modified to adapt to altered orientation relative to the gravity vector.

Adult↗

PubMed1997

Effect of body orientation with respect to gravity on directional accuracy of human pointing movements.

Errors in pointing to remembered target locations were measured in normal subjects in the upright posture and in a supine or prone lying position, three conditions that differed in the orientation of the moving arm with respect to gravity. Vertical errors, or, more strictly, errors along the body axis, were significantly larger in both supine and prone lying positions as compared with the vertical posture. Subjects' orientation with respect to gravity produced a consistent error pattern, i.e. subjects pointed below the remembered target locations in the vertical posture and above them under the two lying conditions, in the body-related co-ordinates. On the contrary, variable error (the confidence ellipse) was differentially affected by the orientation of the movement trajectory with respect to gravity. In the supine body position the variable error was larger, and in the prone position it was smaller than in the upright posture. The finding of gravity-related bias in pointing errors suggests that the motor programme generated in the lying position is not modified to adapt to an altered orientation with respect to gravity.

Adult↗

PubMed1991

[Visual illusions during the electrical stimulation of the labyrinth].

Transcutaneous electrical stimulation of the labyrinth induced apparent motion of a stationary light source in darkness in normal subjects. This effect is similar to the oculogyric illusion induced by rotatory vestibular stimulation. Monaural anodal stimulation of the right labyrinth evoked apparent movement of the target to the left, whereas cathodal stimulation induced opposite illusion. The threshold current was 0.35-0.6 mA. Binaural bipolar stimuli induced illusory target motion directed to the side of the cathode, the threshold decreased 1.5-2.5 times. Binaural monopolar stimulation induced vertical apparent displacement of a target, the threshold being 1.4-3.0 mA. The amplitude and velocity of illusory target motion increased with current. The subject eyes began to move with much higher currents than those necessary for illusory sensation. It is therefore suggested that the visual illusion is related not to vestibulo-visual interaction but to vestibular effects on the spatial perception system.

Darkness↗

PubMed1990

[The dependence of the changes in vestibular postural reactions on the information content of visual feedback].

Electrical stimulation of the labyrinth in standing subjects induced the body sway predominantly in the frontal plane. Stabilographic response included both early (latency 120-200 ms) and late (200-500 ms) components. Their magnitudes depended on the visual control condition. Maximal responses were recorded in the eyes-closed condition. The response decreased when subjects maintained erect posture with their eyes closed, when fixing a stable visual target, and when tracking the frontal stabilogram displayed on an oscilloscope screen (visual feedback). In all the conditions the early component decreased by 10-20 percent whereas the late one decreased by 50-70 percent. Visual fixation of a small light stationary relative to the head did not influence the response. On the other hand, information on the direction of the expected body sway given in the visual fixation condition resulted in a considerable and approximately equal decrease of the two components (by 70-80 percent). It is concluded that the early and late components of the vestibulo-motor response are mediated via different mechanisms with specific temporal and functional characteristics.

Adult↗

PubMed1989

[Changes in the direction of vestibulomotor responses in the process of adaptation to prolonged static head turning in man].

Vestibulomotor responses were studied in normal blindfold subjects in the upright posture during adaptation to maintaining the head turned to the left up to the extreme position for 10 min. The head was maintained in that position either passively or actively. In 5 out of 12 subjects tested, adaptation to the unusual head position resulted in a gradual decrease of the appreciated angle of the head position. The error in appreciating the head position reached as much as 70-80 degrees. The direction of the vestibulomotor response was found to change in parallel with the appreciated head orientation. Thus, under mismatch between the perceived and actual head positions the direction of the vestibulomotor response corresponded to the spatial perception rather than to the actual head orientation.

Adaptation, Physiological↗

PubMed1988

[Effect of real and illusory movements on the human vestibulomotor reaction].

Lateral stabilographic responses to galvanic labyrinth stimulation were studied in healthy subjects in the standing posture. The responses increased during the body tilt forward performed either voluntarily or involuntarily as a result of vibration of the tibialis anterior muscles. The illusory body tilt forward induced by the vibration of the triceps surae muscles under mechanical fixation of the trunk resulted in similar increase of the vestibulomotor response. It is concluded that the enhancement of the vestibulomotor responses during voluntary movements is mediated by the spatial perception system.

Adult↗

PubMed1986

[Spatial perception and vestibulomotor reactions in man].

Postural responses to transcutaneous galvanic stimulation of the right labyrinth were recorded by means of a stabilograph in normal human subjects in various head positions as well as under the illusion of head and trunk rotation induced by vibration of the gluteus maximum muscle. The direction of the vestibulo-motor response was determined by the position of the head: in a normal head position the body swayed in the frontal plane, whereas with the head turned 90 degrees it moved in the sagittal plane. During the illusory head and trunk 90 degrees rotation the responses were sagittally directed like those recorded in the real head-turned-sideways position. When the vibration did not induce the illusion of the head rotation with respect to the feet, the direction of the postural response was determined by the real head orientation. It is concluded that the spatial perception system is involved in the control of spatially oriented vestibulo-motor responses.

Adult↗

PubMed1974