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A Sirigu

Publications and source records attributed to A Sirigu.

At least 19 recordsLinked to original sources
PubMed2006

[The nature of the sense of effort and its neural substrate].

INTRODUCTION: What are the nature and the neural substrate of voluntary force perception? STATE OF ART: Experimental findings demonstrate that efferent signals related to motor command play a dominant role in perceiving voluntary muscular force. This suggests that voluntary force perception is provided through a sense of effort and not through a sense of intramuscular tension. Nevertheless, experimental data show that the contribution of sensory input to effort awareness must not be dismissed. Sensory signals are not involved in generating a signal of effort but rather in calibrating and modulating its magnitude. Neuroimaging and neuropsychological studies revealed that many cortical structures are activated during tasks of voluntary muscular force perception. PERSPECTIVES AND CONCLUSION: In such tasks, the basal ganglia might support the coherence of cortical activity.

Basal Ganglia↗
PubMed2006

Bilateral hand transplantation: six years after the first case.

In this study we present our experience concerning bilateral hand transplantation. Two cases were performed: the first in January 2000 and the second in April 2003. Both recipients received the same immunosuppressive treatment, which was similar to those used in solid organ transplantation, including tacrolimus, prednisone and mycophenolate mofetil while antithymocyte globulins were added for induction. Both recipients presented two episodes of acute rejection (maculopapular lesions) in the first 3 months after transplantation; however, these were easily reversed after a few days increasing oral steroid doses and using topical immunosuppressants. The first recipient presented hyperglycemia and serum sickness while the second recipient suffered a thrombosis of the right ulnar artery and an osteomyelitis of left ulna. All the complications were successfully treated. Functional Magnetic Resonance Imaging (fMRI) showed that cortical hand representation progressively shifted from the lateral to the medial region in the motor cortex. After 6 and 2 years respectively, they showed a relevant sensorimotor recovery particularly of sensibility and activity of intrinsic muscles. They were able to perform the majority of daily activities and to lead a normal social life. The first recipient has been working since 2003. They are both satisfied with their grafted hands.

Adolescent↗
PubMed2004

The influence of hand posture on corticospinal excitability during motor imagery: a transcranial magnetic stimulation study.

In order to study the interaction between proprioceptive information and motor imagery, we herein investigate how compatible and incompatible postural signals influence corticospinal excitability during the mental simulation of hand movements. Subjects were asked to imagine themselves joining the tips of the thumb and the little finger while they maintained one of the two following hand postures: posture A (PA, compatible), little finger, index and thumb extended, the remaining fingers flexed; or posture B (PB, incompatible), index and thumb extended, other fingers flexed. All subjects rated the imagined finger opposition movements as easier to perform when the hand was kept in PA than in PB (P < 0.01) and the correlation between the duration of motor imagery and movement execution was also higher for PA than PB (P < 0.01). For each posture, motor evoked potentials (MEPs) elicited by focal transcranial magnetic stimulation (TMS) of the left motor cortex were recorded from the right opponens pollicis muscle during both motor imagery (MI) and rest (R) conditions. MEP area varied according to the hand posture: PA induced a higher increase in corticospinal excitability, when compared with PB. These results indicate that the actual limb posture affects the process of motor imagery. The source of this postural modulation effect is discussed.

Adult↗
PubMed2003

Illusory movements of the paralyzed limb restore motor cortex activity.

In humans, limb amputation or brachial plexus avulsion (BPA) often results in phantom pain sensation. Actively observing movements made by a substitute of the injured limb can reduce phantom pain, Proc. R. Soc. London B Biol. Sci. 263, 377-386). The neural basis of phantom limb sensation and its amelioration remains unclear. Here, we studied the effects of visuomotor training on motor cortex (M1) activity in three patients with BPA. Functional magnetic resonance imaging scans were obtained before and after an 8-week training program during which patients learned to match voluntary "movements" of the phantom limb with prerecorded movements of a virtual hand. Before training, phantom limb movements activated the contralateral premotor cortex. After training, two subjects showed increased activity in the contralateral primary motor area. This change was paralleled by a significant reduction in phantom pain. The third subject showed no increase in motor cortex activity and no improvement in phantom pain. We suggest that successful visuomotor training restores a coherent body image in the M1 region and, as a result, directly affects the experience of phantom pain sensation. Artificial visual feedback on the movements of the phantom limb may thus "fool" the brain and reestablish the original hand/arm cortical representation.

Adult↗
PubMed2003

Renal size and function in patients with neuropathic bladder due to myelomeningocele: the role of growth hormone.

PURPOSE: Patients with spina bifida have smaller kidneys than healthy individuals. We evaluated the correlation between small size and decreased renal function, and the possible role of growth hormone deficiency. MATERIALS AND METHODS: A total of 54 patients (mean age 11.5 years, median 11, standard deviation +/- 4.52) were healthy except for neuropathic bladder due to spina bifida. Renal function was evaluated with mercaptoacetyltriglycine renal scintigraphy and creatinine clearance. Renal anatomy was evaluated with renal ultrasound and voiding cystourethrography. Serum insulin-like growth factor-1 (IGF-1) levels were measured in all patients with immunoradiometric assay. Renal measurements in our patients were compared using the Sutherland nomogram. RESULTS: A total of 22 patients (41%) had smaller kidneys than normal subjects and 31 appeared to have creatinine clearance values lower than 120 ml per minute per 1.73 m2. The statistical comparison between kidney size and creatinine clearance was significant (p <0.05, r = 0.381). Scintigraphic data showed total effective renal plasma flow less than 568 ml per minute per 1.73 m2 body surface area (normal mean value for age). Comparison between effective renal plasma flow and creatinine clearance was significant (p <0.05, r = 0.31). Serum levels of IGF-1 were normal for age in all patients (mean 332.06 ng/ml, median 303.4, range 39.4 to 732.3). CONCLUSIONS: The kidneys are smaller in patients with spina bifida than in healthy subjects when compared using the Sutherland nomogram. There is a significant correlation between smaller renal length and decreased renal function in all patients, even in those who are healthy except for neurogenic bladder secondary to spina bifida. IGF-1 levels were normal for age, and, therefore, these patients had no growth hormone deficiency. These findings call into question the hypothesis that growth hormone deficiency contributes to smaller kidney size. Other hypotheses can be suggested, such as a defect of embryological growth secondary to malformation, or the result of a defect in homocysteine-methionine metabolism.

Adolescent↗
PubMed2001

Motor and visual imagery as two complementary but neurally dissociable mental processes.

Recent studies indicate that covert mental activities, such as simulating a motor action and imagining the shape of an object, involve shared neural representations with actual motor performance and with visual perception, respectively. Here we investigate the performance, by normal individual and subjects with a selective impairment in either motor or visual imagery, of an imagery task involving a mental rotation. The task involved imagining a hand in a particular orientation in space and making a subsequent laterality judgement. A simple change in the phrasing of the imagery instructions (first-person or third-person imagery) and in actual hand posture (holding the hands on the lap or in the back) had a strong impact on response time (RT) in normal subjects, and on response accuracy in brain-damaged subjects. The pattern of results indicates that the activation of covert motor and visual processes during mental imagery depends on both top-down and bottom-up factors, and highlights the distinct but complementary contribution of covert motor and visual processes during mental rotation.

Astrocytoma↗
PubMed2001

Action planning in a virtual context after prefrontal cortex damage.

Patients with frontal lobe lesions are known to encounter severe problems in the organisation of their behaviour in everyday life. Script generation tasks assess the subject's conceptual ability to formulate and evaluate a coherent and structured plan of action. In the present study, we investigated to what extent neuropsychological deficits observed at the conceptual level of action knowledge lead to impairments in action execution. We examined seven patients with prefrontal cortex damage and sixteen normal subjects. Subjects were first asked to verbally formulate a plan of action and then to use this knowledge for 'executing' the actions in a virtual 3-dimensional interactive apartment presented on a computer screen. The results indicated that the presence of the realistic context improved patients' performance. However, specific impairments were observed in patients in the execution condition, namely actions slips, omissions, failure in initiating actions and purposeless displacements. Moreover, an analysis of planning time showed that, differently of the patients group, normal subjects spent more time during plan execution as compared to plan generation. These results suggest that after a frontal lobe lesion a defective formulation of a routine plan might affect the execution of the corresponding course of actions.

Adult↗
PubMed2001

Script knowledge after severe traumatic brain injury.

Severe diffuse traumatic brain injury (TBI) may impair the performance of daily-life complex activities. The aim of the present study was to assess whether these difficulties are related to a representational impairment of action knowledge. Two tasks requiring the manipulation of scripts were used. The first (script reconstitution) required subjects to sort cards describing actions belonging to 4 different scripts, presented in a random order. The second (script generation) required subjects to generate actions belonging to a given script. The results showed that TBI patients had preserved access to goal representation and action knowledge. However, they demonstrated (1) significant impairments when they had to deal with simultaneous competing sources of information and (2) a lack of inhibitory control on routine overlearned skills. Patients' performance was significantly correlated with behavioral modifications in everyday life. These data suggest that action impairment in severe TBI patients cannot be attributed to an impairment of action knowledge per se. As previously suggested by Schwartz et al., a restriction of limited-capacity processing resources may account for the observed deficits.

Activities of Daily Living↗
PubMed2000

How patients with Parkinson's disease retrieve and manage cognitive event knowledge.

Several studies have pointed out that basal ganglia are involved in adaptive control of action at both motor and cognitive level. This study aimed to investigate how basal ganglia retrieve and manage script event knowledge required in planning behavior. Script event knowledge was investigated in patients with Parkinson's Disease using three kinds of activity that differed in familiarity. Unlike patients with prefrontal lesions, patients with Parkinson's Disease were able to order events in a typical sequence and obeyed the boundaries and hierarchies between events. In contrast, patients with Parkinson's Disease were impaired in evaluating how important each script event was within the context of goal-oriented planning activity. Our findings indicate that the prefrontal cortex and the basal ganglia are differentially involved in planning. The role of the basal ganglia might consist in providing a feedback about the goodness of each action while building up meaningful sequences of events during learning.

Adult↗
PubMed2000

Differential amygdala responses to winning and losing: a functional magnetic resonance imaging study in humans.

The amygdala has been shown to respond to many distinct types of affective stimuli, including reward and punishment feedback in animals. In humans, winning and losing situations can be considered as reward and punishment experiences, respectively. In this study, we used functional magnetic resonance imaging (fMRI) to measure regional brain activity when human subjects were given feedback on their performance during a simple response time task in a fictitious competitive tournament. Lexical stimuli were used to convey positive 'win' or negative 'lose' feedback. The frequency of positive and negative trials was parametrically varied by the experimenters independently from the subjects' actual performance and unbeknownst to them. The results showed that the parametric increase of winning was associated with left amygdala activation whereas the parametric increase of losing was associated with right amygdala activation. These findings provide functional evidence that the human amygdala differentially responds to changes in magnitude of positive or negative reinforcement conveyed by lexical stimuli.

Adult↗
PubMed2000

Partially overlapping neural networks for real and imagined hand movements.

Neuroimagery findings have shown similar cerebral networks associated with imagination and execution of a movement. On the other hand, neuropsychological studies of parietal-lesioned patients suggest that these networks may be at least partly distinct. In the present study, normal subjects were asked to either imagine or execute auditory-cued hand movements. Compared with rest, imagination and execution showed overlapping networks, including bilateral premotor and parietal areas, basal ganglia and cerebellum. However, direct comparison between the two experimental conditions showed that specific cortico-subcortical areas were more engaged in mental simulation, including bilateral premotor, prefrontal, supplementary motor and left posterior parietal areas, and the caudate nuclei. These results suggest that a specific neuronal substrate is involved in the processing of hand motor representations.

Adult↗
PubMed1999

Impaired anticipatory finger grip-force adjustments in a case of cerebellar degeneration.

We describe adjustments in grip force as a consequence of fluctuations in inertial load force during vertical movements of the upper limb in a patient with cerebellar degeneration. Normally grip force is adapted to load-force fluctuations, in particular to the maximum load force, which occurs early in upward movements and late in downward movements. Increased grip force during movement was observed in the patient, but the timing of maximum grip force was not different between upward and downward movements. This suggests impaired cerebellar prediction of the dynamic consequences of voluntary movement.

Adaptation, Physiological↗
PubMed1999

Distinct prefrontal activations in processing sequence at the sentence and script level: an fMRI study.

Neuropsychological studies have shown that the prefrontal cortex is important in planning and monitoring everyday behaviour. In this study, using functional magnetic resonance imaging (fMRI), we investigated whether specific prefrontal regions are involved in processing a sequence of actions. Subjects were required to perform two different tasks: Script-event order and Sentence-word order. Script sequence and word sequence processing were found to activate partially overlapping areas which are known to be implicated in language processing. In addition, the Script-task activated a large area in the dorsolateral prefrontal cortex (Brodmann area 6 and 8, BA 6 and 8), in both the left and right hemispheres, as well as the left supplementary motor area and left angular gyrus (BA 39). Our results suggest that these prefrontal areas may be more specifically involved in the process of analysing sequential links in the action domain.

Adult↗
PubMed1999

Perception of self-generated movement following left parietal lesion.

Three apraxic patients with lesions in the left parietal cortex were required to execute finger movements with either hand, while the visual feedback they received about the movement was manipulated systematically. We used a device which allowed us to present on a video monitor either the patient's hand or the examiner's hand simultaneously performing an identical or a different movement. In each trial, patients were required to decide whether the hand shown on the screen was their own or not. Hand movements produced in response to verbal command included simple (single-finger extension) and complex gestures (multi-finger extension). Ownership judgements were analysed and compared with those produced by six normal controls and two non-apraxic neurological patients. Apraxic patients and controls accurately recognized their own hand on the screen (own movement condition) and correctly identified the viewed hand as the examiner's when it performed a movement different from their own movement (incongruent movement condition). However, when the viewed hand was the examiner's hand executing their own movement (congruent movement condition), apraxic patients were significantly more impaired than controls. When the results were analysed as a function of gesture type, the number of correct responses was significantly lower for apraxic patients with respect to controls only for complex gestures. Interestingly, when patients executed the finger gestures inaccurately, they still failed to recognize the examiner's hand as alien, and claimed that the correct movement presented on the screen was their own. These results confirm that parietal lesions alter the representational aspects of gestures, and suggest a failure in evaluating and comparing internal and external feedback about movement. We conclude that the parietal cortex plays an important role in generating and maintaining a kinaesthetic model of ongoing movements.

Aged↗
PubMed1998

Deficit in evaluating pre-determined sequences of script events in patients with Parkinson's disease.

The purpose of the present study was to assess how the striato-frontal system contributes to the manipulation of goal-directed actions. We studied a group of ten patients with Parkinson's disease (PD) in order to investigate which aspects of action knowledge processing are impaired and to define the conditions under which the deficits may occur. PD patients committed errors of sequence and inserted distractors in tasks that required them to order pre-determined events belonging to a given script in a typical sequence. Rather than attributing errors of event sequencing to a deficit of script "syntax" knowledge, we suggest that the difficulties manifested by PD patients were due to an impairment of a switching mechanism that is necessary for processing information in parallel.

Adult↗
PubMed1998

Distinct frontal regions for processing sentence syntax and story grammar.

Time is a fundamental dimension of cognition. It is expressed in the sequential ordering of individual elements in a wide variety of activities such as language, motor control or in the broader domain of long range goal-directed actions. Several studies have shown the importance of the frontal lobes in sequencing information. The question addressed in this study is whether this brain region hosts a single supramodal sequence processor, or whether separate mechanisms are required for different kinds of temporally organised knowledge structures such as syntax and action knowledge. Here we show that so-called agrammatic patients, with lesions in Broca's area, ordered word groups correctly to form a logical sequence of actions but they were severely impaired when similar word groups had to be ordered as a syntactically well-formed sentence. The opposite performance was observed in patients with dorsolateral prefrontal lesions, that is, while their syntactic processing was intact at the sentence level, they demonstrated a pronounced deficit in producing temporally coherent sequences of actions. Anatomical reconstruction of lesions from brain scans revealed that the sentence and action grammar deficits involved distinct, non-overlapping sites within the frontal lobes. Finally, in a third group of patients whose lesions encompassed both Broca's area and the prefrontal cortex, the two types of deficits were found. We conclude that sequence processing is specific to knowledge domains and involves different networks within the frontal lobes.

Analysis of Variance↗
PubMed1996

The mental representation of hand movements after parietal cortex damage.

Recent neuroimagery findings showed that the patterns of cerebral activation during the mental rehearsal of a motor act are similar to those produced by its actual execution. This concurs with the notion that part of the distributed neural activity taking place during movement involves internal simulations, but it is not yet clear what specific contribution the different brain areas involved bring to this process. Here, patients with lesions restricted to the parietal cortex were found to be impaired selectively at predicting, through mental imagery, the time necessary to perform differentiated finger movements and visually guided pointing gestures, in comparison to normal individuals and to a patient with damage to the primary motor area. These results suggest that the parietal cortex is important for the ability to generate mental movement representations.

Adult↗