PubMed Health⌕ Search

Biomedical subjects

V Gurfinkel

Publications and source records attributed to V Gurfinkel.

10 recordsLinked to original sources
PubMed1998

Proprioceptive information processing in weightlessness.

The "illusions" experiment carried out on five astronauts during the last two French-Russian flights (Antarès in 1992 and Altaïr in 1993) and in the Russian Post-Antarès mission (1993) was designed to investigate the adaptive changes in human proprioceptive functions occurring in weightlessness at both the sensorimotor and cognitive levels, focusing on two kinds of responses: (1) whole-body postural reflexes, and (2) whole-body movement perception. These kinesthetic and motor responses were induced using the tendon-vibration method, which is known to selectively activate the proprioceptive muscular sensory channel and to elicit either motor reactions or illusory movement sensations. Vibration (70 Hz) was therefore applied to ankle (soleus or tibialis) and neck (splenii) muscles. The subject's whole-body motor responses were analyzed from EMG and goniometric recordings. The perceived vibration-induced kinesthetic sensations were mimicked by the subjects with a joystick. The main results show that a parallel in-flight attenuation of the vibration-induced postural responses and kinesthetic illusions occurred, which seems to indicate that the proprioceptive system adapts to the microgravity context, where standing posture and conscious coding of anteroposterior body movements are no longer relevant. The same sensory messages are used at the same time in different sensory motor loops and in the coding of newly developed behavioral movements under microgravity. These results suggest that the human proprioceptive system has a high degree of adaptive functional plasticity, at least as far as the perceptual and motor aspects are concerned.

Adaptation, Physiological↗
PubMed1997

Is the erect posture in microgravity based on the control of trunk orientation or center of mass position?

In the present experiments carried out in microgravity two questions were addressed. First, when the subject was instructed to adopt a vertical erect posture in microgravity with his feet fixed to the floor of the space cabin, would he control anteroposterior position with respect to the ankle joint axis of the "vertical projection" of his center of mass (CM) or trunk axis orientation with respect to the "vertical" (perpendicular to the floor of the space cabin)? Secondly, is CM anteroposterior position regulated during upper trunk movements in microgravity, in the absence of equilibrium constraint? Two subjects were tested in a long-term space flight. Video camera recordings were performed and analyzed off line. The results show that during erect vertical posture in microgravity, the trunk axis with respect to the "vertical" is inclined some 7 degrees forward. The anteroposterior position of the CM "vertical" projection is not shifted forward, as might be expected in view of the trunk inclination, but remains close to the ankle joint axis. At the end of the upper trunk forward or backward bending movement, the final position of the vertical CM projection remains close to the ankle joint axis in microgravity. These results are interpreted as indicating that CM anteroposterior position continues to be accurately controlled in microgravity; the forward inclination of the trunk axis observed in microgravity is interpreted as being due to a misevaluation of the "vertical" axis on the basis of biased information from proprioceptive inputs.

Analysis of Variance↗
PubMed1995

Is there an effect of weightlessness on mental rotation of three-dimensional objects?

We studied the performance of eight cosmonauts in a mental rotation paradigm with simultaneously presented perspective views of three-dimensional objects. The cosmonauts were tested successively on earth, in microgravity aboard the Russian MIR station and again on earth. Their performance was compared to performance of a control group of five subjects tested on earth on the same dates. We particularly tried to disambiguate the effect of microgravity, procedural bias and practice. Our results show that the microgravity did not alter the mental rotation process. The performance of cosmonauts increased with practice, similarly to the performance of control group's subjects suggesting that the weightlessness did not impair implicit learning as well. Finally, we propose an explanation of previous contradictory results.

Adult↗
PubMed1995

Proprioceptive coordination of discrete movement sequences: mechanism and generality.

A "discrete" movement sequence is defined as a movement with a single goal that involves a series of overlapping joint rotations. Reaching-and-grasping and throwing are examples of discrete movement sequences. The central nervous system (CNS) can use reafferent proprioceptive information from one joint rotation in a sequence to coordinate subsequent rotations at other joints. The experiments reported in this paper demonstrate how the human CNS uses proprioceptive information to coordinate discrete movement sequences. We examined the mechanism (at an information processing level) underlying proprioceptive coordination and the generality (i.e., the boundary conditions) of these mechanisms as they apply to everyday movement sequences. Adult human subjects performed a discrete movement sequence that resembles backhand throwing: elbow extension followed by hand opening. The task was to open the hand as the elbow passed through a prescribed "target" angle. We eliminated visual information and made the arrival time at the target angle unpredictable so that the available kinematic information was provided exclusively by proprioception. The subjects were capable of performing this motor task with a high degree of precision, thereby demonstrating that the nervous system can use proprioceptive input to coordinate discrete movement sequences. Our data indicate that precise coordination is achieved by extracting kinematic information related to both the velocity of elbow rotation as well as the elbow position during movement (i.e., "dynamic position"). Dynamic position information appears to be encoded as both absolute joint angle and angular distance, although more precisely as angular distance. Although our experiments were conducted under rather restrictive laboratory conditions, this mechanism of motor coordination might also apply to everyday movement. Our results suggest that this mechanism could be employed for passive as well as active movement sequences, with and without opposing loads; it could exert its influence in discrete movement sequences as brief as 210 ms or as long as 1.5 s; and it does not involve any significant degree of learning (this proprioceptive mechanism appears to be readily available for use on the first attempt of a novel motor task).

Adult↗
PubMed1995

Independence of bilateral symmetry detection from a gravitational reference frame.

Data were collected during three orbital flights aboard the Russian MIR space station from eight cosmonauts tested on a bilateral symmetry detection task. It is known that on earth subjects' performance is significantly superior for a vertical or horizontal than for an obliquely oriented axis of symmetry, giving a so-called oblique effect. The present results show that this oblique effect did not disappear in microgravity. They confirm that the detection of visual symmetry is not tied to a gravitational reference frame. An unexpected result of the experiments was that practice reduced the reaction time for detection of asymmetrical patterns below that for symmetrical patterns. This result suggests the presence of two separate detection processes. The detection of symmetry, being useful for the efficient encoding of visual information, is well developed in naive subjects. Extensive practice on a symmetry-detection task, however, increases the efficacy of the asymmetry-detection process.

Adult↗
PubMed1993

Effects of prolonged weightlessness on mental rotation of three-dimensional objects.

Previous experiments have suggested that the analysis of visual images could be a gravity-dependent process. We investigated this hypothesis using a mental rotation paradigm with pictures of three-dimensional objects during a 26-day orbital flight aboard the Soviet MIR station. The analysis of cosmonauts' response times showed that the mental rotation task is not greatly impaired in weightlessness. On the contrary, there are indications of a facilitation as: (1) the average rotation time per degree was shorter inflight than on the ground; (2) this difference seemed to be particularly marked for stimuli calling for roll axis rotations. However several factors may be responsible for this difference which was not obvious in one subject. Further experiments will have to test if this effect is really due to exposure to microgravity.

Adult↗
PubMed1993

Sensorimotor and perceptual function of muscle proprioception in microgravity.

Adaptive properties of the human proprioceptive systems were studied during the French-Soviet orbital flight (Aragatz mission, December 1988). The present space experiment investigated the hypothesis that the modifications of both biomechanical and physiological conditions occurring under microgravity involve considerable reorganization of body perception and postural control. The proprioceptive information originating in muscles is known to contribute, together with visual, vestibular, and sole cutaneous information to postural regulation. Moreover, by specifically activating the proprioceptive channel, muscle vibration is able to elicit both illusory movement sensations and postural responses. This experimental tool was used in microgravity in order to test various aspects of muscle sensory function. Ankle flexor and extensor vibration was applied under different experimental conditions. Quantitative analysis of motor responses was carried out on leg muscle EMG, goniometric, and kinesigraphic recordings. Joystick recordings and astronauts' comments were used to describe the kinaesthetic sensations. The main results were as follows: 1) Under microgravity, the sensitivity of muscle receptors remains unchanged. 2) During the flight, the tonic vibration reflexes (TVR) increased significantly in flexor muscles, which exhibited a sustained tonic activity. 3) The whole-body postural responses normally induced by ankle flexor muscle vibration were suppressed, whereas they remained unchanged or were only reduced when vibrations were applied to the ankle extensor muscles. In all cases, the postural response velocity decreased. 4) A disfacilitation of the vibration-induced postural illusions was observed to occur during long-term exposure to microgravity. These illusions became atypical however. For example: body lift illusion could be induced by tibialis anterior muscle vibration, whereas it was never induced in the controls. The characteristics of the illusory body movements described under normal gravity can be restored by artificially increasing the axial foot support forces during the flight. In conclusion, these data suggest that a functional reorganization of the proprioceptive information processing occurs in microgravity, affecting both perceptual and motor aspects of behavior. It is possible that these proprioceptive adaptations may be partly attributable to the new whole-body propulsive foot functions imposed by exposure to weightlessness and to the adaptation of motor behavior to the third dimension of space.

Adaptation, Physiological↗
PubMed1993

Axial synergies under microgravity conditions.

Fast forward and backward upper trunk movements were analyzed and compared under microgravity and under preflight and postflight conditions. The kinematic analysis showed that the upper trunk movements were accompanied by hip and knee movements in the opposite direction both under microgravity and under normal gravitational conditions. This suggests that the center of mass position with respect to the feet is still regulated under microgravity when the feet are attached to the floor. The EMG analysis during backward movements shows that under preflight conditions a set of muscles (ErSp, BF, Sol) in the back of the body are activated early on. Under microgravity, the early Sol activation was replaced by an early TA activation, which was still present at the first postflight recording and was then replaced by the early Sol activation observed under preflight conditions. This finding shows that the EMG pattern underlying the axial synergies is flexible and that adaptive changes take place both under microgravity and after return to Earth.

Adaptation, Physiological↗
PubMed1992

[Strategy and synergy: two levels of equilibrium control during movement. Effects of the microgravity].

Equilibrium is ensured during forward or backward upper trunk movements by displacing the hip and knee simultaneously in opposite directions. When fast movements are performed, a muscle synergy characterized by the early activation of a set of trunk, thigh and leg muscles precedes the onset of the kinematic changes. The question which is addressed concerns the possibility that two levels of equilibrium control might exist during upper trunk movements: the strategy level, which is relatively invariant, is characterized by the displacement in opposite directions of the upper and low segments, and the muscle synergy level at which the strategy is implemented, which may be adaptable to the environmental constraints. When upper trunk movements are performed under microgravity with the subject's feet fixed to the floor of the space cabin, the displacement of upper and lower body segments in opposite directions still occurs, although this is no longer necessary to maintain the equilibrium. This kinematic strategy seems to be aimed at regulating the centre of inertia position with respect to the feet. The muscle synergies associated with these kinematic changes are modified, however, under microgravity. After returning to the ground, the previous synergies do not reappear immediately, but only after a few days. This suggests that a short period of learning is needed to change the synergy. These data are compatible with the hypothesis that two levels of equilibrium control actually exist during upper trunk movements, the strategy level, which is kinematic and invariant, and the synergy level, which is adaptable to the environmental constraints through a short learning process.

Electromyography↗