Biomedical subjects

Y Rossetti

Publications and source records attributed to Y Rossetti.

At least 37 records · Page 2Linked to original sources

PubMed2002

Bilateral vestibular stimulation does not improve visual hemineglect.

This work compared the effect of unilateral (right and left) and bilateral vestibular stimulation in a right-brain-damaged patient with neglect. Neglect was improved following left caloric vestibular stimulation, and worsened following right vestibular stimulation. On the other hand, no modification of neglect was observed after bilateral vestibular stimulation. These results support the idea that caloric vestibular stimulation may improve neglect through a specific effect; bilateral stimulation making the putative activation bilateral and symmetrical does not affect the lateral bias of neglect.

Aged↗

PubMed2001

Grasping the past. delay can improve visuomotor performance.

"Optic ataxia" is caused by damage to the human posterior parietal cortex (PPC). It disrupts all components of a visually guided prehension movement, not only the transport of the hand toward an object's location, but also the in-flight finger movements pretailored to the metric properties of the object. Like previous cases, our patient (I.G.) was quite unable to open her handgrip appropriately when directly reaching out to pick up objects of different sizes. When first tested, she failed to do this even when she had previewed the target object 5 s earlier. Yet despite this deficit in "real" grasping, we found, counterintuitively, that I.G. showed good grip scaling when "pantomiming" a grasp for an object seen earlier but no longer present. We then found that, after practice, I.G. became able to scale her handgrip when grasping a real target object that she had previewed earlier. By interposing catch trials in which a different object was covertly substituted for the original object during the delay between preview and grasp, we found that I.G. was now using memorized visual information to calibrate her real grasping movements. These results provide new evidence that "off-line" visuomotor guidance can be provided by networks independent of the PPC.

Animals↗

PubMed2001

Prism adaptation to rightward optical deviation improves postural imbalance in left-hemiparetic patients.

Left-hemiparetic patients show predominant postural imbalance as compared to right-hemiparetic patients. The right hemisphere is crucial for generating internal maps used for perceptual and premotor processing of spatial information. Predominant postural imbalance with right-brain damage could thus result from a distortion of an internal postural map. Well-known manifestations of distorted internal maps due to right-hemisphere lesions, such as hemineglect, may show improvement following prism adaptation shifting the visual field to the right. We therefore investigated the effect of prism adaptation on postural imbalance in left-hemiparetic patients. Three groups of five patients were either adapted to prisms deviating the visual field to the right or left or exposed to neutral prisms while performing reaching movements of the right arm. Postural imbalance was reduced only following prism adaptation to the right. Thus, brief adaptation (i.e., 3 min) to rightward-shifting prisms can dramatically improve postural imbalance. This result shows that the effect of exposure to prisms that horizontally shift the visual field to the right in a reaching task generalizes to the postural system, and it suggests an interaction between horizontal and vertical reference frames. This also supports the theory that predominant postural imbalance in patients with right-brain damage may be partly related to a distortion of an internal postural map.

Adult↗

PubMed2001

Attentional processing of colour and location cues.

The aim of the present experiment was to investigate attentional processing of colour and location cues using a detection task. Subjects were required to respond to cued corners of a line drawing of a three-dimensional cube. Both cue and target were highlighted in red or green in one corner of the cube. Cues could be valid or invalid with respect to both the colour and location of subsequent targets. Results indicated a significant main effect of location validity, but no main effect of colour validity. Results also indicated that significant colour cueing effects were evident when location cues were invalid. These data also suggested different time courses for the processing of location and colour information. Location validity effects were largest at the shortest interstimulus interval (ISI) and decreased slightly with increasing ISI. In contrast, colour validity effects were absent at the shortest ISI, but thereafter increased with increasing ISI. The results of this experiment indicate that colour cues can be effective even in an inherently spatial task, provided there is sufficient time for the processing of colour information.

Adolescent↗

PubMed2001

Prism adaptation improves representational neglect.

Previous work has shown that various symptoms of unilateral neglect, including the pathological shift of the subjective midline to the right, may be improved by a short adaptation period to a prismatic shift of the visual field to the right. We report here, in two neglect patients the improvement of imagery neglect after prism exposure. Despite a strong neglect observed for mental images, as well as for conventional tests, the mental evocation of left-sided information from an internal image of the map of France was fully recovered following prism adaptation to the right. This improvement could not be explained by the alteration of visuomotor responses induced by the prism adaptation. Therefore, prism adaptation may act not only on sensory-motor levels but also on a higher cognitive level of mental space representation and/or exploration.

Adaptation, Physiological↗

PubMed2001

[Role of rehabilitation in hemineglect syndromes].

Unilateral neglect syndrome compromises functional outcome of left hemiparetic patients. Treatment of this syndrome is a challenge in motor rehabilitation in order to reduce the incapacity and improve the prognosis. In this study, we present a review of the literature focusing on the different rehabilitation techniques proposed and their theoretical basis: improvement of the ability to maintain attention, improvement of spatial selective attention by implicit or explicit cueing, reduction of rightward orienting bias by sensory manipulations. Recently, we reported the improvement of symptoms of unilateral neglect syndrome after a prism adaptation to a rightward optical deviation. Unlike previous physiological manipulations used to improve neglect, this improvement lasted for at least two hours after prism removal. These results are most promising for rehabilitation programs. They may be linked to a stimulation of a short-term plasticity of brain functions and underline the interest of action in rehabilitation of neglect.

Adaptation, Physiological↗

PubMed2000

Cognitive bias induced by visuo-motor adaptation to prisms: a simulation of unilateral neglect in normal individuals?

Unilateral neglect has been recently shown to be improved following a short period of adaptation to wedge prisms. The present study investigates whether visuo-motor adaptation can generate a bias in normals on line bisection tasks classically used to assess unilateral neglect. Our results show that adaptation to left-deviating prisms induces a stronger rightward bias for the perceptual than the motor line bisection task. This bias is in the same direction as the one observed in unilateral neglect. No significant effect is produced by adaptation to right-deviating prisms. Our data confirm that the plasticity of inter-sensory and sensori-motor coordinations affects higher levels of space representation. These asymmetric results may reflect the inherent bias of the brain's structural organisation and provide an empirical explanation for the left-sided predominance of unilateral neglect.

Adaptation, Physiological↗

PubMed2000

An 'automatic pilot' for the hand in human posterior parietal cortex: toward reinterpreting optic ataxia.

We designed a protocol distinguishing between automatic and intentional motor reactions to changes in target location triggered at movement onset. In response to target jumps, but not to a similar change cued by a color switch, normal subjects often could not avoid automatically correcting fast aiming movements. This suggests that an 'automatic pilot' relying on spatial vision drives fast corrective arm movements that can escape intentional control. In a patient with a bilateral posterior parietal cortex (PPC) lesion, motor corrections could only be slow and deliberate. We propose that 'on-line' control is the most specific function of the PPC and that optic ataxia could result from a disruption of automatic hand guidance.

Adult↗

PubMed1998

Prism adaptation to a rightward optical deviation rehabilitates left hemispatial neglect.

A large proportion of right-hemisphere stroke patients show hemispatial neglect-a neurological deficit of perception, attention, representation, and/or performing actions within their left-sided space, inducing many functional debilitating effects on everyday life, and responsible for poor functional recovery and ability to benefit from treatment. The frequent parietal locus of the lesion producing neglect reflects the impairment of coordinate transformation used by the nervous system to represent extrapersonal space. Given that adaptation to a visual distortion can provide an efficient way to stimulate neural structures responsible for the transformation of sensorimotor coordinates, the aim of our study was to investigate the effect of prism adaptation on various neglect symptoms, including the pathological shift of the subjective midline to the right. All patients exposed to the optical shift of the visual field to the right were improved on their manual body-midline demonstration and on classical neuropsychological tests. Unlike other physiological manipulations used to improve neglect, this improvement lasted for at least two hours after prism removal and thus could be useful in rehabilitation programmes. The positive effect found for both sensorimotor and more cognitive spatial functions suggests that they share or depend on a common level of space representation linked to multisensory integration.

Adaptation, Ocular↗

PubMed1998

Implicit short-lived motor representations of space in brain damaged and healthy subjects.

This article reviews experimental evidence for a specific sensorimotor function which can be dissociated from higher level representations of space. It attempts to delineate this function on the basis of results obtained by psychophysical experiments performed with brain damaged and healthy subjects. Eye and hand movement control exhibit automatic features, such that they are incompatible with conscious control. In addition, they rely on a reference frame different from the one used by conscious perception. Neuropsychological cases provide a strong support for this specific motor representation of space, which can be spared in patients with lesions of primary sensory systems who have lost conscious perception of visual, tactile or proprioceptive stimuli. Observation of these patients also showed that their motor behavior can be "attracted" by a goal only under specific conditions, that is, when the response is immediate and when no cognitive representation of this goal is elaborated at the same time. Beyond the issue of the dissociation between an implicit motor representation and more cognitive processing of spatial information, the issue of the interaction between these two systems is thus a matter of interest. It is suggested that the conscious, cognitive representation of a stimulus can contaminate or override the short-lived motor representation, but no reciprocal influence seem to occur. The interaction observed in patients can also be investigated in normals. The literature provides examples of interaction between sensorimotor and cognitive framing of space, which confirm that immediate action is not mediated by the same system as delayed action, and that elaborating a categorial representation of the action goal prevents the expression of the short-lived sensorimotor representation. It is concluded that action can be controlled by a sensory system which is specialized for on-line processing of relevant goal characteristics. The temporal constraints of this system are such that it can affect the action before a full sensory analysis of this goal has been completed. The performance obtained on the basis of this spatial sensory processing suggests that short-lived motor representations may rather be considered as real "presentation" of the action world, which share its metric properties.

Brain↗

PubMed1998

The timing of color and location processing in the motor context.

In this study, the use of color and location as stimulus attributes manipulated during a simple action was aimed at comparing how dorsal (location) and ventral (color) features are integrated in action and the timing of their processing. Eighteen subjects were presented with a green dot on a computer screen, which they were required to point at and touch. In 20% of the trials, the location or the color of the target was altered at the onset of movement to this stimulus, requiring the participant to modify the initially programmed response according to specific motor instructions. In the 'location-go' group, the target changed in location and participants were instructed to reach the displaced stimulus by correcting their ongoing movement. In the 'location-stop' and 'color-stop' groups, subjects were instructed to interrupt their movement when the target changed location or color, respectively. Results showed that the latency of the first responses to the perturbation clearly depended on the stimulus attribute and not on the motor instruction tested: the response to color change was obtained about 80 ms later than both conditions involving location change. It is concluded that: (1) color processing is slower than location processing, and (2) the first reactions to the location change occur after the same delay irrespective of the response required from the subject.

Adult↗

PubMed1998

From eye to hand: planning goal-directed movements.

The nature of the neural mechanisms involved in movement planning still remains widely unknown. We review in the present paper the state of our knowledge of the mechanisms whereby a visual input is transformed into a motor command. For the sake of generality, we consider the main problems that the nervous system has to solve to generate a movement, that is: target localization, definition of the initial state of the motor apparatus, and hand trajectory formation. For each of these problems three questions are addressed. First, what are the main results presented in the literature? Second, are these results compatible with each other? Third, which factors may account for the existence of incompatibilities between experimental observations or between theoritical models? This approach allows the explanation of some of the contradictions existing within the movement-generation literature. It also suggests that the search for general theories may be in vain, the central nervous system being able to use different strategies both in encoding the target location with respect to the body and in planning hand displacement. In our view, this conclusion may advance the field by both opening new lines of research and bringing some sterile controversies to an end.

Animals↗

PubMed1997

Visuomotor transformations for reaching to memorized targets: a PET study.

Positron emission tomography (PET) was used to identify cortical and subcortical regions involved in the control of reaching to visual targets. Regional cerebral blood flow (rCBF) was measured in eight healthy subjects using H2(15)O PET during the performance of three different tasks. All tasks required central fixation while a 400-ms target was flashed every 5 s at a random location around a virtual circle centered on the fixation target. Additional instructions differed according to the task: (i) visual detection of the target without overt responses; (ii) immediate pointing to the most recent target in the sequence, and (iii) pointing to the previous target in the sequence. By design, the two motor tasks differed in the cognitive processing required. In each trial of immediate pointing, the spatial location of only the most recent target needed to be processed. In each trial of pointing to the previous, instead, while the most recent target was stored in memory for the movement of the next trial, the previous target had to be retrieved from memory to direct the current movement. Limb trajectories were comparable between the two motor tasks in terms of most spatiotemporal parameters examined. Significant rCBF increases were identified using analysis of covariance and t statistics. Compared with visual detection there was activation of primary sensorimotor cortex, ventrolateral precentral gyrus, inferior frontal gyrus in the opercular region, supramarginal gyrus, and middle occipital gyrus, all these sites in the hemisphere (left) contralateral to the moving limb, and cerebellar vermis, during both immediate pointing and pointing to the previous. During immediate pointing there was additional activation of left inferior parietal lobule close to the intraparietal sulcus, and when compared with pointing to the previous, dorsolateral prefrontal cortex bilaterally. During pointing to the previous, instead, there was additional activation of supplementary motor cortex, anterior and midcingulate, and inferior occipital gyrus in the left hemisphere; superior parietal lobule, supramarginal gyrus, and posterior hippocampus in the right hemisphere; lingual gyri and cerebellar hemispheres bilaterally; anterior thalamus; and pulvinar. The activation of two partially distinct cerebral networks in these two motor tasks reflects the different nature of signal processing involved. In particular, the specific activation of intraparietal sulcus and prefrontal cortex in immediate pointing appears characteristic of a network for visuospatial working memory. By contrast, the corticolimbic network engaged in pointing to the previous could mediate spatial attention and the sequence of encoding, recording, and decoding of spatial memories required by a dual task with two competing targets.

Adult↗

PubMed1997

Viewing the hand prior to movement improves accuracy of pointing performed toward the unseen contralateral hand.

It is now well established that the accuracy of pointing movements to visual targets is worse in the full open loop condition (FOL; the hand is never visible) than in the static closed loop condition (SCL; the hand is only visible in static position prior to movement onset). In order to account for this result, it is generally admitted that viewing the hand in static position (SCL) improves the movement planning process by allowing a better encoding of the initial state of the motor apparatus. Interestingly, this wide-spread interpretation has recently been challenged by several studies suggesting that the effect of viewing the upper limb at rest might be explained in terms of the simultaneous vision of the hand and target. This result is supported by recent studies showing that goal-directed movements involve different types of planning (egocentric versus allocentric) depending on whether the hand and target are seen simultaneously or not before movement onset. The main aim of the present study was to test whether or not the accuracy improvement observed when the hand is visible before movement onset is related, at least partially, to a better encoding of the initial state of the upper limb. To address this question, we studied experimental conditions in which subjects were instructed to point with their right index finger toward their unseen left index finger. In that situation (proprioceptive pointing), the hand and target are never visible simultaneously and an improvement of movement accuracy in SCL, with respect to FOL, may only be explained by a better encoding of the initial state of the moving limb when vision is present. The results of this experiment showed that both the systematic and the variable errors were significantly lower in the SCL than in the FOL condition. This suggests: (1) that the effect of viewing the static hand prior to motion does not only depend on the simultaneous vision of the goal and the effector during movement planning; (2) that knowledge of the initial upper limb configuration or position is necessary to accurately plan goal-directed movements; (3) that static proprioceptive receptors are partially ineffective in providing an accurate estimate of the limb posture, and/or hand location relative to the body; and (4) that static visual information significantly improves the representation provided by the static proprioceptive channel.

Fingers↗

PubMed1996

Early visual experience affects memorization and spatial representation of proprioceptive targets.

Five subjects who had been blind from an early age and five age-matched blindfolded sighted subjects were engaged in a spatial memory task. Locations to be memorized were presented on a sagittal plane by passive positioning of the left index finger. A go signal for matching the target location with the right index finger was provided 0 or 8 s after left hand positioning. Constant errors in amplitude and direction of movement and pointing distribution observed after the longer delay differed across groups. Pointing variability was higher in the blindfolded sighted group. In addition, the main axis of pointing distributions obtained in the blindfolded sighted group were aligned with the target array for the 8 s but not the 0 s delay. By contrast, the main axis tended to be aligned with movement direction for blind subjects for both delays. These results suggest that memorizing a proprioceptively defined target may involve distinct spatial representations according to delay and to early visual experience.

Adult↗

PubMed1996

Grasping without form discrimination in a hemianopic field.

Although patients with blindsight are usually unable to discriminate forms, recent neuropsychological data have suggested that they could still use some form attributes in object-oriented actions. One patient with a complete right hemianopia due to a medial occipital lesion has been tested for his capacities to process orientation and size of visual objects. He was presented with either a slot of variable orientation or with rectangular objects of the same surface but variable length. His performance was studied in three types of tasks: motor, in which he had to insert a card in the slot or to grasp the rectangle between thumb and indexfinger; verbal, in which forced-choice verbal guesses were required; and matching, which required matching orientation or size with wrist or fingers. Although responses were at chance level in the two latter conditions, motor responses were systematically influenced by both orientation and size of the stimulus. These data provide further evidence for two dissociable modes of visual information processing dealing respectively with 'what"' the object is vs 'how' to grasp it. They also indicate that the neural pathway controlling visuomotor transformation in humans is much less dependent on V1 input than the pathway involved in visual discrimination and identification.

Adult↗

PubMed1996

Integrated control of hand transport and orientation during prehension movements.

At a descriptive level, prehension movements can be partitioned into three components ensuring, respectively, the transport of the arm to the vicinity of the target, the orientation of the hand according to object tilt, and the grasp itself. Several authors have suggested that this analytic description may be an operational principle for the organization of the motor system. This hypothesis, called "visuomotor channels hypothesis," is in particular supported by experiments showing a parallelism between the reach and grasp components of prehension movements. The purpose of the present study was to determine whether or not the generalization of the visuomotor channels hypothesis, from its initial form, restricted to the grasp and transport components, to its actual form, including the reach orientation and grasp components, may be well founded. Six subjects were required to reach and grasp cylindrical objects presented at a given location, with different orientations. During the movements, object orientation was either kept constant (unperturbed trials) or modified at movement onset (perturbed trials). Results showed that both wrist path (sequence of positions that the hand follows in space), and wrist trajectory (time sequence of the successive positions of the hand) were strongly affected by object orientation and by the occurrence of perturbations. These observations suggested strongly that arm transport and hand orientation were neither planned nor controlled independently. The significant linear regressions observed, with respect to the time, between arm displacement (integral of the magnitude of the velocity vector) and forearm rotation also supported this view. Interestingly, hand orientation was not implemented at only the distal level, demonstrating that all the redundant degrees of freedom available were used by the motor system to achieve the task. The final configuration reached by the arm was very stable for a given final orientation of the object to grasp. In particular, when object tilt was suddenly modified at movement onset, the correction brought the upper limb into the same posture as that obtained when the object was initially presented along the final orientation reached after perturbation. Taken together, the results described in the present study suggest that arm transport and hand orientation do not constitute independent visuomotor channels. They also further suggest that prehension movements are programmed, from an initial configuration, to reach smoothly a final posture that corresponds to a given "location and orientation" as a whole.

Adult↗

PubMed1996

Inverse relationship between sensation of effort and muscular force during recovery from pure motor hemiplegia: a single-case study.

A 39-year-old patient with a right pure motor hemiplegia, who complained of a striking sensation of effort when he performed a movement, was regularly examined during 4 months. The effort sensation and the force recovery have been measured during the execution of upper limb movements: shoulder antepulsion up to horizontal, supined elbow flexion up to horizontal and full hand digital grip. The subject was asked to realize a movement with the paretic arm and to concentrate on the felt effort; then he had to perform the same movement against a resistance with the healthy arm, until the perceived heaviness matched the effort sensation felt on the other side. Recovery of force and evolution of effort sensation did not follow linear trends over time. The curves displayed significant steps and plateaus, which were mainly observed for the proximal movements. The steps tended to be clustered within a few days, consistent with crucial periods in the restoration process. Within these, significant reduction of the effort sensation and increase of the force were together observed. These critical moments of the motor recovery could be analyzed as the result of an improvement of the neural traffic in the internal capsule and an activation of specific structures involved in the representation of the force and effort.

Adult↗