Biomedical subjects

A Farnè

Publications and source records attributed to A Farnè.

13 recordsLinked to original sources

PubMed2004

Patterns of spontaneous recovery of neglect and associated disorders in acute right brain-damaged patients.

OBJECTIVES: The evolutionary pattern of spontaneous recovery from acute neglect was studied by assessing cognitive deficits and motor impairments. Detailed lesion reconstruction was also performed to correlate the presence of and recovery from neglect to neural substrates. METHODS: A consecutive series of right brain-damaged (RBD) patients with and without neglect underwent weekly tests in the acute phase of the illness. The battery assessed neglect deficits, neglect-related deficits, and motor impairment. Age-matched normal subjects were also investigated to ascertain the presence of non lateralised attentional deficits. Some neglect patients were also available for later investigation during the chronic phase of their illness. RESULTS: Partial recovery of neglect deficits was observed at the end of the acute period and during the chronic phase. Spatial attention was impaired in acute neglect patients, while non spatial attentional deficits were present in RBD patients with and without acute neglect. A strong association was found between acute neglect and fronto-parietal lesions. Similar lesions were associated with neglect persistence. In the chronic stage, neglect recovery was paralleled by improved motor control of the contralesional upper limb, thus emphasising that neglect is a negative prognostic factor in motor functional recovery. CONCLUSIONS: These findings show that spatial attention deficits partially improve during the acute phase of the disease in less than half the patients investigated. There was an improvement in left visuospatial neglect at a later, chronic stage of the disease, but this recovery was not complete.

Acute Disease↗

PubMed2003

Visuo-motor control of the ipsilateral hand: evidence from right brain-damaged patients.

We investigated the extent to which the right hemisphere is involved in the control of the ipsilateral hand by analysing the kinematics of right-hand prehension in right brain-damaged (RBD) patients. We required patients to grasp one of five possible objects, equally-sized and distributed over a 40 degrees wide workspace. With the purpose of investigating the right hemisphere contribution to the on-line visuo-motor control, we also assessed patients' ability to correct their movement "in-flight", in response to a sudden change of object position. Patients' performance was compared to that of aged-matched controls. A Younger group of healthy subjects, matching the population classically tested on double-step paradigms, was also evaluated to fully assess whether patients' kinematics could be partially due to normal ageing. As a further aim, the possible influence of hemispatial neglect was evaluated by comparing the performances of right brain-damaged patients with and without neglect. In normal subjects, the results confirmed and extended the notion of (a). positional tuning of grip formation, and (b). fast reactions following a change in object position. In addition, subtle effects of ageing on visuo-motor behaviour were shown by less efficient movement correction in the Elderly group. Patients executing reach-to-grasp actions into the left contralesional hemispace were selectively affected in both temporal and spatial aspects of movements. While their performances were relatively well preserved in the right hemispace, patients did not show positional tuning of grip formation, nor fast corrections of their movements when acting in the left hemispace. Interestingly, similar deficits were found irrespective of the presence of neglect. These results show that the right hemisphere contributes to the processing of visuo-motor information that is necessary for executing actions with the ipsilateral hand in the contralateral space.

Adult↗

PubMed2002

Viewing less to see better.

OBJECTIVE: To assess the efficacy, as well as the long term duration, of a new procedure for the rehabilitation of visuospatial neglect in patients with right hemisphere stroke. METHODS: Patients with right unilateral hemispheric damage identified with neglect were assigned to a treatment (T+) or a control (T-) group. The treatment consisted in abolishing all visual inputs from the right hemispace for one week by means of specially devised hemiblinding goggles. Patients' visuospatial abilities were tested and compared between groups immediately after the week of treatment. Both groups were further assessed one week after treatment suspension for evaluation of long term beneficial effects. RESULTS: Following the treatment, a substantial amelioration of visuospatial neglect symptoms was selectively observed in the T+ group. In contrast, untreated patients showed only weak signs of recovery. Most important, the amelioration obtained in the T+ group of patients was not ephemeral, being significantly maintained after a further period of one week, even after suspension of the treatment. CONCLUSION: The protracted efficacy of the proposed "hemiblinding technique" may have important implications for the recovery of visuospatial neglect and may be a very promising tool for investigating both the cognitive and the neural basis of neglect rehabilitation.

Aged↗

PubMed2001

Auditory peripersonal space in humans: a case of auditory-tactile extinction.

Animal experiments have shown that the spatial correspondence between auditory and tactile receptive fields of ventral pre-motor neurons provides a map of auditory peripersonal space around the head. This allows neurons to localize a near sound with respect to the head. In the present study, we demonstrated the existence of an auditory peripersonal space around the head in humans. In a right-brain damaged patient with tactile extinction, a sound delivered near the ipsilesional side of the head extinguished a tactile stimulus delivered to the contralesional side of the head (cross-modal auditory-tactile extinction). In contrast, when an auditory stimulus was presented far from the head, cross-modal extinction was dramatically reduced. This spatially specific cross-modal extinction was found only when a complex sound like a white noise burst was presented; pure tones did not produce spatially specific cross-modal extinction. These results show a high degree of functional similarity between the characteristics of the auditory peripersonal space representation in humans and monkeys. This similarity suggests that analogous physiological substrates might be responsible for coding this multisensory integrated representation of peripersonal space in human and non-human primates.

Aged↗

PubMed2000

Hand kinematics during reaching and grasping in the macaque monkey.

In this paper, we develop an animal model of prehension movements by examining the kinematics of reaching and grasping in monkeys and by comparing the results to published data on humans. Hand movements were recorded in three dimensions in monkeys who were trained to either point at visual targets under unperturbed and perturbed conditions, or to reach and grasp 3-D objects. The results revealed the following three similarities in the hand kinematics of monkey and man. (1) Pointing movements showed an asymmetry depending on target location relative to the hand used; in particular, movements to an ipsilateral target took longer than those to a contralateral one. (2) Perturbation of target location decreased the magnitude of the velocity peak and increased the duration of pointing movements. (3) Reaching to grasp movements displayed a bell-shaped wrist velocity profile and the maximum grip aperture was correlated with object size. These similarities indicate that the macaque monkey can be a useful model for understanding human motor control.

Animals↗

PubMed2000

Dynamic size-change of hand peripersonal space following tool use.

Humans and monkeys share similar sensory integrated processing of tactile and peri-hand visual inputs for coding peripersonal space surrounding the hand. In monkeys, tool use is known to induce a transient elongation of hand-centred peripersonal space along the tool axis. Here we report evidence that, also in humans, the use of a tool can increase the spatial extent of the representation of peri-hand visual space to incorporate the tool. We investigated this phenomenon in patients with tactile extinction, by using a cross-modal paradigm well suited to reveal visual-tactile integration near patients' hand. In the present study cross-modal extinction was assessed far from patients' ipsilesional hand, at the distal edge of a hand-held rake. We found that cross-modal extinction was more severe after patients used the rake to retrieve distant objects with respect to a condition in which the rake was not used. This evidence of an expansion of peri-hand space lasted only a few minutes after tool use. By contrast, peri-hand space expansion was not observed when motor actions towards distant objects did not involve the tool. These findings show that visual peri-hand space has important dynamic properties in humans; it can be expanded and contracted depending upon tool use.

Aged↗

PubMed2000

Seeing or not seeing where your hands are.

Previous findings have demonstrated the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. A strong modulatory effect of vision on touch perception was found when a visual stimulus was presented near the hand. In contrast, when the visual stimulus was presented far from the hand, only a weak modulatory effect was found. The aim of the present study was to verify whether such cross-modal links between touch and vision in the peripersonal space centered on the hand could be mediated by proprioceptive signals specifying the current hand positions or if they directly reflect an interaction between two sensory modalities, i.e., vision and touch. To this aim, cross-modal effects were studied in two different experiments: one in which patients could see their hands and one in which vision of their hands was prevented. The results showed strong modulatory effects of vision on touch perception when the visual stimulus was presented near the seen hand and only mild effects when the vision of the hand was prevented. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand, and corresponding visual receptive fields in the space immediately adjacent to the tactile fields. One important feature of these bimodal neurons is that their responsiveness to visual stimuli delivered near the body part is reduced or even extinguished when the view of the body part is prevented. This implies that, at least for the hand, the vision of the hand is crucial for determining the spatial mapping between vision and touch that takes place in the peripersonal space. In contrast, the proprioceptive signals specifying the current hand position in space do not seem to be relevant in determining the cross-modal interaction between vision and touch.

Aged↗

PubMed2000

Left tactile extinction following visual stimulation of a rubber hand.

In close analogy with neurophysiological findings in monkeys, neuropsychological studies have shown that the human brain constructs visual maps of space surrounding different body parts. In right-brain-damaged patients with tactile extinction, the existence of a visual peripersonal space centred on the hand has been demonstrated by showing that cross-modal visual-tactile extinction is segregated mainly in the space near the hand. That is, tactile stimuli on the contralesional hand are extinguished more consistently by visual stimuli presented near the ipsilesional hand than those presented far from it. Here, we report the first evidence in humans that this hand-centred visual peripersonal space can be coded in relation to a seen rubber replica of the hand, as if it were a real hand. In patients with left tactile extinction, a visual stimulus presented near a seen right rubber hand induced strong cross-modal visual-tactile extinction, similar to that obtained by presenting the same visual stimulus near the patient's right hand. Critically, this specific cross-modal effect was evident when subjects saw the rubber hand as having a plausible posture relative to their own body (i.e. when it was aligned with the subject's right shoulder). In contrast, cross-modal extinction was strongly reduced when the seen rubber hand was arranged in an implausible posture (i. e. misaligned with respect to the subject's right shoulder). We suggest that this phenomenon is due to the dominance of vision over proprioception: the system coding peripersonal space can be 'deceived' by the vision of a fake hand, provided that its appearance looks plausible with respect to the subject's body.

Aged↗

PubMed1999

Are perception and action affected differently by the Titchener circles illusion?

In the present study, we investigated the effects of the Titchener circles illusion in perception and action. In this illusion, two identical discs can be perceived as being different in size when one is surrounded by an annulus of smaller circles and the other is surrounded by an annulus of larger circles. This classic size-contrast illusion, known as Ebbinghaus or Titchener Circles Illusion, has a strong perceptual effect. By contrast, it has recently been demonstrated that when subjects are required to pick up one of the discs, their grip aperture during reaching is largely appropriate to the size of the target. This result has been considered as evidence of a clear dissociation between visual perception and visuomotor behaviour in the intact human brain. In this study, we suggest and investigate an alternative explanation for these results. We argue that, in a previous study, while perception was subjected to the simultaneous influence of the large and small circles displays, in the grasping task only the annulus of circles surrounding the target object was influential. We tested this hypothesis by requiring 18 subjects to perceptually estimate and grasp a disc centred in a single annulus of Titchener circles. The results showed that both the perceptual estimation and the hand shaping while grasping the disc were similarly influenced by the illusion. Moreover, the stronger the perceptual illusion, the greater the effect on the grip scaling. We discuss the results as evidence of an interaction between the functional pathways for perception and action in the intact human brain.

Adult↗

PubMed1998

In search of biased egocentric reference frames in neglect.

The present study was aimed at assessing, by means of visual as well as proprioceptive-kinaesthetic straight-ahead tasks, the possible causal role of the ipsilesional deviation of the egocentric reference frame in determining neglect syndrome. The hypothesis, originally proposed by Ventre et al. [3], that an alteration of the representation of body-centred space can be a cause of asymmetrical spatial behaviour in humans has been recently revived by Karnath and co-workers [24]. The results of the present study seem to challenge the view that a systematic ipsilesional displacement of the egocentric reference is the crucial mechanism responsible for unilateral visual neglect. Under visual conditions, in which patients were required to stop a moving spot as it crossed their perceived midline, the ipsilesional deviation of the egocentric reference frame was dependent upon the direction of visual scanning. Right to left visual scanning direction produced a rightward displacement of the egocentric reference. In contrast, left to right visual scanning direction allowed neglect patients to correctly locate their perceived egocentre with an accuracy which did not differ from controls. The notion that the effect of a deviation of the egocentric reference frame is actually dependent on a bias in the visual scanning orienting response was also confirmed in the proprioceptive straight-ahead pointing tasks, in which the patients were blindfolded and therefore no visual information was available. In these conditions, in which patients were required to judge the subjective midline by using head, trunk and shoulder co-ordinate systems, the displacement of the subjective egocentric midline was not present.

Adult↗

PubMed1998

Visual peripersonal space centred on the face in humans.

A convergent series of studies in monkeys and man suggests that the computation of visual space is performed in several brain regions for different behavioural purposes. Among these multiple spatial areas, the ventral intraparietal cortex, the putamen and the ventral aspect of the premotor cortex (area 6) contain a system for representing visual space near the face (peripersonal space). In these cerebral areas some neurons are bimodal: they have tactile receptive fields on the face, and they can also be driven by visual stimuli located near the tactile field. The spatial correspondence between the visual and tactile receptive fields provides a map of near visual space coded in body-part-centred co-ordinates. In the present study we demonstrate for the first time the existence of a visual peripersonal space centred on the face in humans. In patients with right hemispheric lesions, visual stimuli delivered in the space near the ipsilesional side of the face extinguished tactile stimuli on the contralesional side (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). Furthermore, a visual stimulus presented in the proximity of the contralesional side of the face improved the detection of a left tactile stimulus: i.e. under bilateral tactile presentation patients were more accurate to report the presence of a left tactile stimulus when a simultaneous visual stimulus was presented near the left side of the face. However, when visual stimuli were delivered far from the face, visuotactile extinction and visuotactile facilitation effects were dramatically reduced. These findings are consistent with the hypothesis of a representation of visual peripersonal space coded in bodypart-centred co-ordinates, and they provide a striking demonstration of the modularity of human visual space.

Adult↗

PubMed1998

Neuropsychological evidence of an integrated visuotactile representation of peripersonal space in humans.

Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patient"s ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patient"s hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.

Aged↗

PubMed1994

Neglect determined by the relative location of responses.

The aim of the present study was to assess the relevance of relative position coding of the effectors in the determination of neglect for the space of response. Two groups of patients were selected: an experimental group, consisting of right brain-damaged patients with left unilateral neglect, and a control group, consisting of right brain-damaged patients without unilateral neglect. These patients participated in two different experiments. In Experiment 1 the stimuli were horizontally aligned to the left and the right of a fixation stimulus; in Experiment 2 they were vertically aligned above and below the fixation stimulus. The stimuli consisted either of the number '1' or the number '2'. In both experiments, the patient was required to give a relative left key press response upon presentation of number '1' and a relative right key press response upon presentation of number '2'. The responses were recorded using the index and middle fingers of the right hand and the response keyboard was located on the right side of body midline. In each experiment there were two hand response conditions: standard and reversed. Under the former condition the hand was in the normal upright position; under the latter, the hand and the response keyboard were rotated by approximately 180 degrees. Under the standard condition, the two effectors were located on the typical anatomical spatial position, i.e. the index finger, which was located on the left relative position, pressed the left key, and the middle finger, which was located on the right relative position, pressed the right key. Under the reversed condition, the positions of the two effectors were reversed, i.e. the middle finger located on the left relative spatial position pressed the left key and the index finger, located on the right relative spatial position, pressed the right key. The results for both experiments showed that neglect patients were always slower to respond when the task required a left key response. The effect was manifest under both the standard and the reversed conditions. The neglect was therefore for the space of response and not for the anatomical spatial position of the effectors.

Adult↗