1,720,966 research outputs found
Basi nervose dell'agnosia per le parti corporee e le azioni umane
No full textLa percezione visiva di facce e stimoli corporei non facciali porta all’attivazione di
distinte aree corticali. Inoltre, nonostante sia intimamente collegata, l’azione e la
forma corporea sembrano essere rappresentate in distinti sistemi neurali. Studi di
lesioni cerebrali hanno mostrato specifici disturbi associati con l’elaborazione del
volto umano, tuttavia non vi sono nella letteratura scientifica prove dell’esistenza di
disturbi specifici per il riconoscimento di parti del corpo non facciali. Nel presente
studio è stata dimostrata, attraverso la combinazione di paradigmi psicofisici e
tecniche avanzate di analisi e mappatura lesionale, la presenza di disturbi di
riconoscimento di facce o di parti del corpo non facciali in seguito a lesioni corticali
che coinvolgono rispettivamente la corteccia occipitale ventro-mediale o la corteccia
occipitale laterale. Inoltre, sono stati documentati disturbi di riconoscimento visivo
specifici per la forma o l’azione di parti del corpo umano escluse le facce, associati
rispettivamente ad una lesione nelle regioni occipito-temporali oppure nelle aree
premotorie. Questi disturbi categoria-specifici, chiamati agnosia per il corpo e
l’azione umana, ci suggeriscono che l'analisi visiva di stimoli costituiti da parti del
corpo umano possa essere effettuata da almeno due sistemi corticali, le aree posteriori
occipitotemporali, implicate nell’elaborazione dell’identità corporea e le aree
premotorie, coinvolte nell’analisi dell’azione osservata, indipendentemente
dall’identità del soggetto agente.Visual analysis of faces and non-facial body stimuli brings about neural activity in
different cortical areas. Moreover, even if inherently linked, body form and body
action may be represented in separate neural substrates. Brain lesion studies show
specific face processing deficits but neuropsychological evidence for defective
recognition of non-facial body parts is lacking. Combining psychophysics and lesionmapping
techniques we found that brain lesions specifically affecting the ventromedial
and lateral occipital cortex induce visual recognition deficits of face and nonfacial
body parts respectively. Moreover, we discovered recognition impairments
specifically affecting the form or the action of non-facial body stimuli and causatively
associated with lesions to occipito-temporal and premotor areas respectively. These
category-specific deficits, called body form and body action agnosia, suggest that
visual processing of non-facial body parts is based on a cortical division of labour
with occipito-temporal areas actively linked to processing body identity and premotor
areas to processing body action independent from the actors’ identity
Il contributo della neuropsicologia: disturbi dello schema corporeo in seguito a lesioni cerebrali
No full text
Anosognosia for apraxia: Experimental evidence for defective awareness of one's own bucco-facial gestures.
No full textAnosognosia is a multifaceted, neuro-psychiatric syndrome characterized by defective awareness of a variety of perceptuo-motor, cognitive or emotional deficits. The syndrome is also characterized by modularity, i.e. deficits of awareness in one domain (e.g. spatial perception) co-existing with spared functions in another domain (e.g. memory). Anosognosia has mainly been reported after right hemisphere lesions. It is however somewhat surprising that no studies have thus far specifically explored the possibility that lack of awareness involves apraxia, i.e. a deficit in the ability to perform gestures caused by an impaired higher-order motor control and not by low-level motor deficits, sensory loss, or failure to comprehend simple commands. We explored this issue by testing twelve fifteen patients with vascular lesions who were assigned to one of three groups depending on their neuropsychological profile and brain lesion. The patients were asked to execute various actions involving the upper limb or bucco-facial areas. In addition they were also asked to judge the accuracy of these actions, either performed by them or by other individuals. The judgment of the patients was compared to that of two external observers.
Results show that our bucco-facial apraxic patients manifest a specific deficit in detecting their own gestural errors. Moreover they were less aware of their defective performance in bucco-facial as compared to limb actions. Our results hint at the existence of a new form of anosognosia specifically involving apraxic deficits
Implicit awareness in anosognosia for hemiplegia: unconscious interference without conscious re-representation.
No full textSome patients with anosognosia for hemiplegia, i.e. apparent unawareness of hemiplegia, have been clinically observed to show ‘tacit’ or ‘implicit’ awareness of their deficits. Here we have experimentally examined whether implicit and explicit responses to the same deficit-related material can dissociate. Fourteen stroke patients with right hemisphere lesions and contralesional paralysis were tested for implicit and explicit responses to brief sentences with deficit-related themes. These responses were elicited using: (i) a verbal inhibition test in which patients had to inhibit completing each sentence with an automatic response (implicit task) and (ii) a rating procedure in which patients rated the self-relevance of the same sentences (explicit task). A group of anosognosic hemiplegic patients was significantly slower than a control group of aware hemiplegic patients in performing the inhibition task with deficit-related sentences than with other emotionally negative themes (relative to neutral themes). This occurred despite their explicit denial of the self-relevance of the former sentences. Individual patient analysis showed that six of the seven anosognosic patients significantly differed from the control group in this dissociation. Using lesion mapping procedures, we found that the lesions of the anosognosic patients differed from those of the ‘aware’ controls mainly by involving the anterior parts of the insula, inferior motor areas, basal ganglia structures, limbic structures and deep white matter. In contrast, the anosognosic patient without implicit awareness had more cortical lesions, mostly in frontal areas, including lateral premotor regions, and also in the parietal and occipital lobes. These results provide strong experimental support for a specific dissociation between implicit and explicit awareness of deficits. More generally, the combination of our behavioural and neural findings suggests that an explicit, affectively personalized sensorimotor awareness requires the re-representation of sensorimotor information in the insular cortex, with possible involvement of limbic areas and basal ganglia circuits. The delusional features of anosognosia for hemiplegia can be explained as a failure of this re-representation
Massive somatic deafferentation and motor deefferentationof the lower part of the body impair its visual recognition: apsychophysical study of patients with spinal cord injury
No full textEmbodied cognition theories postulate that perceiving and understanding the body states of other individuals are underpinned by
the neural structures activated during first-hand experience of the same states. This suggests that one’s own sensorimotor system
may be used to identify the actions and sensations of others. Virtual and real brain lesion studies show that visual processing of
body action and body form relies upon neural activity in the ventral premotor and the extrastriate body areas, respectively. We
explored whether visual body perception may also be altered in the absence of damage to the above cortical regions by testing
healthy controls and spinal cord injury (SCI) patients whose brain was unable to receive somatic information from and send motor
commands to the lower limbs. Participants performed tasks investigating the ability to visually discriminate changes in the form or
action of body parts affected by somatosensory and motor disconnection. SCI patients showed a specific, cross-modal deficit in
the visual recognition of the disconnected lower body parts. This deficit affected both body action and body form perception,
hinting at a pervasive influence of ongoing body signals on the brain network dedicated to visual body processing. Testing SCI
patients who did or did not practise sports allowed us to test the influence of motor practice on visual body recognition. We found
better upper body action recognition in sport-practising SCI patients, indicating that motor practice is useful for maintaining visual
representation of actions after deafferentation and deefferentation. This may be a potential resource to be exploited for
rehabilitation
Vision of the body modulates processing in primary somatosensory cortex
No full textViewing the body affects somatosensory processing, even when entirely non-informative about stimulation. While several studies have reported effects of viewing the body on cortical processing of touch and pain, the neural locus of this modulation remains unclear. We investigated whether seeing the body modulates processing in primary somatosensory cortex (SI) by measuring short-latency somatosensory evoked-potentials (SEPs) elicited by electrical stimulation of the median nerve while participants looked directly at their stimulated hand or at a non-hand object. Vision of the body produced a clear reduction of the P27 component of the SEP recorded over contralateral parietal channels, which is known to reflect processing in SI. These results provide the first direct evidence that seeing the body modulates processing in SI and demonstrate that vision can affect even the earliest stages of cortical somatosensory processing
Contextual bottom-up and implicit top-down modulation of anarchic hand syndrome: A single-case report and a review of the literature
No full textAnarchic hand syndrome (AHS) is a rare neurological condition characterized by seemingly purposeful, goal-directed hand movements which the person afflicted by the syndrome is not, however, in control of. By extensively examining a patient with AHS we provide novel neuropsychological and lesion mapping data that shed new light on the possibility of modulating specific symptoms associated with AHS, in particular unilateral apraxia and magnetic apraxia. Moreover, we compared lesion mapping data with an in depth analysis of previous studies in order to explore the neural network responsible for the complex symptomatology associated with this syndrome. We found that non-primarily motor variables (e.g. the nature of the object to be grasped and integration of visuo-spatial feedback in action) play an important role in determining AHS symptomatology. Moreover, we found that lesions involving various different parts of the motor control network (the corpus callosum, the anterior cingulate cortex and the supplementary motor area, the parietal areas and thalamus) are closely linked to partially differing AHS symptoms. The comparison of our data with those reported in previous studies indicate that AHS is a multifaceted and complex syndrome in which the influence of non-primarily motor, emotional and higher-order components may be largely underestimated
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