Search PubMed⌕ Search

Biomedical subjects

Y Rossetti

Publications and source records attributed to Y Rossetti.

49 records · Page 3Linked to original sources
PubMed1995

Implicit processing of somaesthetic information: a dissociation between where and how?

We present the case of a patient with a lesion of the thalamus who was completely anaesthetized on his right side. He was unable to detect and describe a tactile stimulus applied to his affected right arm, but could direct his normal left hand toward the specific right hand site where the stimulus had been applied when so instructed ('blind touch'). Strikingly, this pointing ability disappeared when the patient had to indicate on a picture of an arm where the stimulus was applied, and when he had to name the stimulus location during his pointing. Similar results were also obtained for localizing the unfelt fingertip ('blind proprioception'). Neuropsychological case studies have demonstrated that brain lesions can produce reciprocal dissociations between object identification (what is the object) and object-oriented action (how to direct a movement to the object). Along these lines, it is suggested that our patient exhibited a dissociation between a 'where' system and a 'how' system for tactile and proprioceptive stimuli.

Cerebral Hemorrhage↗
PubMed1995

Representation of hand position prior to movement and motor variability.

Pointing accuracy of six human subjects was measured in two blocked conditions where the hand was either never visible (T: target only) or only visible in static position prior to movement onset (H+T: hand+target). It was shown in condition H+T that, viewing the hand prior to movement greatly decreased end-point variability compared with condition T. This effect was associated with a significant modification of the movement kinematics: the H+T condition induced a shortened acceleration phase with a corresponding lengthened deceleration phase, compared with the T condition. These results led us to the hypothesis that viewing the hand prior to movement onset allowed a decrease of pointing variability through a feedback process. This hypothesis was further tested by turning the target off during the deceleration phase of the movement at half peak velocity. It was shown that turning the target off had no effect upon the T condition but induced a significant increase of pointing variability in the H+T condition. This result suggests that vision of the static hand enhances the proprioceptive localization of the limb and allows for a better visual to kinesthesic feedback.

Adult↗
PubMed1995

Vectorial coding of movement: vision, proprioception, or both?

1. Subjects were asked to point toward visual targets without visual reafference from the moving hand in two conditions. In both conditions the pointing fingertip was viewed only before movement onset. 2. In one condition, the pointing fingertip was viewed through prisms that created a visual displacement without altering the view of the target. In another experimental condition, vision of the fingertip was not displaced. Comparison of these two conditions showed that virtually shifting finger position before movement through prisms induced a pointing bias in the direction opposite to the shift. The extent of this pointing bias was about one third of the prismatic shift applied to the fingertip. 3. Analysis of movement initial direction demonstrated that it was also less deviated than predicted from the prismatic shift. In addition, the reaction time and movement time of the reaching movement were increased. 4. This result is interpreted in the framework of the vectorial coding of reaching movement. Proprioception and vision provide two possible sources of information about initial hand position, i.e., the origin of the movement vector. The question remains as to how these two sources of information interact in specifying initial hand position when they are simultaneously available. 5. Our results are thus discussed with respect to a visual-to-visual movement vector hypothesis and a proprioceptive-to-visual vector hypothesis. It is argued that the origin of the putative movement vector is encoded by weighted fusion of the visual and the proprioceptive information about hand initial position.

Adult↗
PubMed1995

Postural and synergic control for three-dimensional movements of reaching and grasping.

1. A fundamental question about motor control is related to the nature of the representations used by the nervous system to program the movement. Theoretically, arm displacement can be encoded either in task (extrinsic) or in joint (intrinsic) space. 2. The present study investigated the organization of complex movements consisting of reaching and grasping a cylindrical object presented along different orientations in space. In some trials, object orientation was suddenly modified at movement onset. 3. At a static level, the final limb angles were highly predictable despite the wide range of possible postures allowed by articular redundancy. Moreover, when object orientation was unexpectedly modified at movement onset, the final angular configuration of the limb was identical to that obtained when the object was initially presented along the orientation reached after the perturbation. 4. At a dynamical level, a generalized synergy was observed, and tight correlations were noted between all joint angles implicated in the movement with the exception of elbow flexion. For this joint angle, which did not vary monotonically, strong partial correlations were however observed before and after movement reversal. 5. These results suggest that natural movements are mostly carried out in joint space by postural transitions.

Arm↗
PubMed1994

The effect of viewing the static hand prior to movement onset on pointing kinematics and variability.

Pointing accuracy and arm movement kinematics of six human subjects were measured in three conditions where the hand was never visible during the ongoing movement: (1) in the dark; (2) the static hand was seen in peripheral vision prior to target presentation, but not during the reaction time (H-T); (3) the static hand was seen in peripheral vision until movement onset (H+T). It was shown that: (1) viewing the hand prior to movement decreased pointing variability as compared to the dark condition. (2) Viewing simultaneously hand and target (H+T) and further decreased pointing variability as compared to the H-T condition. This effect was proportional to the reaction time. (3) A lengthening of the deceleration phase was observed for movements performed in the H+T condition, as compared to the other two conditions. (4) A negative correlation between variability and the first part of the deceleration phase was observed in the H+T condition, but neither in the H-T condition nor in the dark. These results suggest that the decrease in pointing variability observed in the H+T condition is due to a feedback based on kinesthetic reafference. Better encoding of the initial position of the hand relative to the target (as in H+T) would allow a calibration of arm position sense, which is used to drive the hand toward the target during the deceleration phase.

Adult↗
PubMed1994

Is there an optimal arm posture? Deterioration of finger localization precision and comfort sensation in extreme arm-joint postures.

Processing of joint redundancy is one of the most important problems in motor control. For instance, gaze orientation can be obtained with an infinite number of eye and head combinations. It has been proposed that a solution to this problem might be the minimization of eye and head position-signal errors. For arm movements, where the excess of degrees of freedom is even higher, cost function was proposed as a criterion for movement selection, reflecting some comfort variable evoked from the peripheral inputs, e.g. optimal muscular energy cost or glucose consumption. However, no biological implication of comfort on motor control has yet been demonstrated. We have further investigated this approach by hypothesizing that arm posture choice also relies on a minimization of position-signal errors arising from individual joints. The prediction is that accuracy of fingertip localization by pointing made by the contralateral hand would be enhanced for comfortable postures of the target arm and degraded for uncomfortable postures using extreme joint positions. Results show an increase in pointing variability when extreme joint postures are used (wrist flexion, shoulder elevation, or both). This increase in pointing variability is proportional to the increase in subjective discomfort rating. Individual joint effects can be added arithmetically into a whole arm value for both discomfort rating and pointing variable and constant error. These results suggest that the choice of comfortable postures for the arm corresponds to an optimization of arm position-signal reliability. This new constraint might be a useful tool for further investigation on posture or trajectory formation.

Arm↗
PubMed1994

Optimal contributions of head and eye positions to spatial accuracy in man tested by visually directed pointing.

Encoding of visual target location in extrapersonal space requires convergence of at least three types of information: retinal signals, information about orbital eye positions, and the position of the head on the body. Since the position of gaze is the sum of the head position and the eye position, inaccuracy of spatial localization of the target may result from the sum of the corresponding three levels of errors: retina, ocular and head. In order to evaluate the possible errors evoked at each level, accuracy of target encoding was assessed through a motor response requiring subjects to point with the hand towards a target seen under foveal vision, eliminating the retinal source of error. Subjects had first to orient their head to one of three positions to the right (0, 40, 80 degrees) and maintain this head position while orienting gaze and pointing to one of five target positions (0, 20, 40, 60, 80 degrees). This resulted in 11 combinations of static head and eye positions, and corresponded to five different gaze eccentricities. The accuracy of target pointing was tested without vision of the moving hand. Six subjects were tested. No systematic bias in finger pointing was observed for eye positions ranging from 0 to 40 degrees to the right or left within the orbit. However, the variability (as measured by a surface error) given by the scatter of hand pointing increased quadratically with eye eccentricity. A similar observation was made with the eye centered and the head position ranging from 0 to 80 degrees, although the surface error increased less steeply with eccentricity. Some interaction between eye and head eccentricity also contributed to the pointing error. These results suggest that pointing should be most accurate with a head displacement corresponding to 90% of the gaze eccentricity. These results explain the systematic hypometry of head orienting towards targets observed under natural conditions: thus the respective contribution of head and eye to gaze orientation might be determined in order to optimize accuracy of target encoding.

Adult↗
PubMed1993

Prismatic displacement of vision induces transient changes in the timing of eye-hand coordination.

Eye-hand coordination was investigated during a task of finger pointing toward visual targets viewed through wedge prisms. Hand and eye latencies and movement times were identical during the control condition and at the end of prism exposure. A temporal reorganization of eye and hand movements was observed during the course of adaptation. During the earlier stage of prism exposure, the time gap between the end of the eye saccade and the onset of hand movement was increased from a control time of 23 to 68 msec. This suggests that a time-consuming process occurred during the early prism-exposure period. The evolution of this time gap was correlated with the evolution of pointing errors during the early stage of prism exposure, in such a way that both measures increased at the onset of prism exposure and decreased almost back to control values within about 10 trials. However, spatial error was not entirely corrected, even late in prism exposure when the temporal organization of eye and hand had returned to baseline. These data suggest that two different adaptive mechanisms were at work: a rather short-term mechanism, involved in normal coordination of spatially aligned eye and hand systems, and a long-term mechanism, responsible for remapping spatially misaligned systems. The former mechanism can be strategically employed to quickly optimize accuracy in a situation involving misalignment, but completely adaptive behavior must await the slower-acting latter mechanism to achieve long-term spatial alignment.

Adult↗
PubMed1990

Heat-induced finger vasoconstriction controlled by skin sympathetic nerve activity.

Finger blood flow (BF) and skin sympathetic nerve activity (SSA) to the glabrous side of the hand were measured during immersion of the hand in a water bath in which temperature (Tw) was raised every 10 min by steps of 2 degrees C from 35 or 37 to 41 degrees C. The experiments were conducted during the summer in rooms in which ambient temperature was 28-32 degrees C or 35 degrees C. The nine healthy male subjects were wearing summer clothes. Finger BF through vessels located deep in the skin was measured by using laser-Doppler flowmetry (ALF-2100, Advance). With the use of a tungsten microelectrode SSA was recorded directly from the median nerve at the wrist or antecubital fossa of the tested arm. With finger vessels already dilated at Tw of 35 or 37 degrees C, finger BF decreased, with a concomitant increase in the SSA bursts as Tw rose to 39-41 degrees C. We confirmed in one subject that anesthetic blockade of the median nerve at the site proximal, but not distal, to the recording site blocked responses to the step rise in Tw in the SSA bursts and in finger BF. From these results we conclude that, with the subject in a warm state, blood vessels of the finger respond to local heating with vasoconstriction, and this finger vasoconstriction is evoked reflexively, largely through the increased sympathetic outflow to the resistance vessels of the finger.

Adult↗
PubMed1988

Prostaglandin E1, prostaglandin E2, and endotoxin failure to produce fever in the Japanese freshwater snail Semisulcospira libertina.

The thermopreferendum (preferred temperature) of the Japanese freshwater snail (Semisulcospira libertina) was determined in an aquatic temperature gradient after injection of prostaglandin E1, prostaglandin E2, and LPS. Injected doses of each pyrogen ranged from a toxic dose to less than 1/20th of the toxic dose. Toxic effect of the highest doses of pyrogen disappeared within 120 min. No fever occurred during the 150 min observation following the pyrogen injection. The present results support the hypothesis that fever was selected as a way of defending against infection only after the period of the emergence of the molluscus, i.e., the early Cambrian period.

Alprostadil↗
PubMed1987

Fever in snails, reflection on a negative result.

1. Groups of aquatic snails (Limnaea auricularia) were placed in a temperature gradient and their thermopreferendum measured. 2. Injected with various amounts of killed Escherichia coli, bacterial endotoxin, human interleukin, and prostaglandin E1, E2 and F2 alpha, they did not develop a fever. 3. High doses of prostaglandins were toxic. 4. These results suggest that fever appeared in the course of evolution after the emergence of molluscs and before that of arthropods.

Animals↗