1,721,065 research outputs found
Implicit functional-semantic evaluation of object symmetry and contralesional visual denial in a case of left unilateral neglect with damage of the dorsal paraventricular white matter.
No full textIt is well documented that right brain damaged patients with left unilateral neglect may show unconscious processing of contralesional stimuli. However, the anatomical correlates of this phenomenon are still not well defined. Here we report the case of a neglect patient with a circumscribed lesion of the dorsal parietal-occipital white matter showing clear implicit processing of the contralesional side of line drawings and object based neglect. The patient was able to perform correct semantic analysis of the symmetry (or asymmetry) of the drawings. Additional testing disclosed denial of the existence of the contralesional side of asymmetrical geometrical shapes with correct perception of symmetrical ones and of shapes without the left side. These findings provide direct evidence supporting a critical role of the dorsal visual system in the activation of conscious representations of visual stimuli
Misrepresentation of horizontal space in left unilateral neglect: role of hemianopia.
No full textRight-brain-damaged patients with left unilateral neglect are reported to misperceive the horizontal extension of contralesional stimuli as being shorter than that of ipsilesional stimuli.To investigate the functional and anatomic correlates of horizontal space misrepresentation.Eight right-brain-damaged patients with contralesional neglect and complete hemianopia (N+H+), nine right-brain-damaged patients with contralesional neglect and no visual field defect (N+H-), and five unilateral brain-damaged patients with contralesional complete hemianopia and no neglect (N-H+) reproduced a horizontal distance (10 cm) in the contralesional and ipsilesional hemispace.N+H+ patients overextended the distance contralesionally and underextended the same distance ipsilesionally. N+H- and N-H+ patients reproduced equivalent distances contralesionally and ipsilesionally. Compared with N+H- patients, N+H+ patients had a greater ipsilesional shift when bisecting horizontal lines; however, these two groups of patients had comparable neglect severity on multiple-item cancellation tasks. In the N+H+ group the area of maximal overlapping of the lesion was in the posterior cerebral lobes.Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect
Misrepresentation of the horizontal space in neglect patients
No full textBackground: Right-brain–damaged patients with left unilateral neglect are reported to misperceive the horizontal extension of contralesional stimuli as being shorter than that of ipsilesional stimuli. Objective: To investi- gate the functional and anatomic correlates of horizontal space misrepresentation. Methods: Eight right-brain–damaged patients with contralesional neglect and complete hemianopia (NH), nine right-brain– damaged patients with contralesional neglect and no visual field defect (NH), and five unilateral brain-damaged patients with contralesional complete hemianopia and no neglect (NH) reproduced a horizontal distance (10 cm) in the contralesional and ipsilesional hemispace. Results: NH patients overextended the distance contralesionally and underextended the same distance ipsilesionally. NH and NH patients reproduced equivalent distances contralesionally and ipsilesionally. Compared with NH patients, NH patients had a greater ipsilesional shift when bisecting horizontal lines; however, these two groups of patients had comparable neglect severity on multiple-item cancellation tasks. In the NH group the area of maximal overlapping of the lesion was in the posterior cerebral lobes. Conclusion: Complete contralesional hemianopia after posterior brain damage is an important factor in determining misrepresentation of horizontal space in patients with left unilateral neglect
The anatomy of neglect without hemianopia: a key role for parietal-frontal disconnection?
No full textWe investigated the anatomical correlates of chronic unilateral neglect in right brain damaged patients with no visual field defects. Independently from basal ganglia or thalamus involvement, neglect patients had a subcortical area of maximal lesion overlap (maxov) in the superior longitudinal fasciculus (SLF). Neglect patients without lesion of subcortical nuclei had an additional maxov area in the rostralmost limit of the supramarginal gyrus (SmG). Patients without neglect showed a maxov area in the corticospinal tract with no involvement of the SLF or SmG. These findings call attention to the role of parietal-frontal disconnection in the pathogenesis of neglect. This disconnection can make neglect generalised and enduring also in patients suffering only partial damage of the parietal-temporal cortex, and who would otherwise show more selective attentional impairments
Attention and predictions: Control of spatial attention beyond the endogenous-exogenous dichotomy
No full textThe mechanisms of attention control have been extensively studied with a variety of methodologies in animals and in humans. Human studies using non-invasive imaging techniques highlighted a remarkable difference between the pattern of responses in dorsal fronto-parietal regions vs. ventral fronto-parietal (vFP) regions, primarily lateralized to the right hemisphere. Initially, this distinction at the neuro-physiological level has been related to the distinction between cognitive processes associated with strategic/endogenous vs. stimulus-driven/exogenous of attention control. Nonetheless, quite soon it has become evident that, in almost any situation, attention control entails a complex combination of factors related to both the current sensory input and endogenous aspects associated with the experimental context. Here, we review several of these aspects first discussing the joint contribution of endogenous and stimulus-driven factors during spatial orienting in complex environments and, then, turning to the role of expectations and predictions in spatial re-orienting. We emphasize that strategic factors play a pivotal role for the activation of the ventral system during stimulus-driven control, and that the dorsal system makes use of stimulus-driven signals for top-down control. We conclude that both the dorsal and the vFP networks integrate endogenous and exogenous signals during spatial attention control and that future investigations should manipulate both these factors concurrently, so as to reveal to full extent of these interactions. © 2013 Macaluso and Doricchi
The contribution of retinotopic and multimodal coding of space to horizontal space misrepresentation in neglect and hemianopia.
No full textThe functions of the temporal–parietal junction
No full textIn the human brain, the temporal-parietal junction (TPJ) is a histologically heterogenous area that includes the ventral portions of the parietal cortex and the caudal superior temporal gyrus sector adjacent to the posterior end of the Sylvian fissure. The anatomical heterogeneity of the TPJ is matched by its seemingly ubiquitous involvement in different cognitive functions that span from memory to language, attention, self-consciousness, and social behavior. In line with established clinical evidence, recent fMRI investigations have confirmed relevant hemispheric differences in the TPJ function. Most importantly, the same investigations have highlighted that, in each hemisphere, different subsectors of the TPJ are putatively involved in different cognitive functions. Here I review empirical evidence and theoretical proposals that were recently advanced to gain a unifying interpretation of TPJ function(s). In the final part of the review, a new overarching interpretation of the TPJ function is proposed. Current advances in cognitive neuroscience can provide important insights that help improve the clinical understanding of cognitive deficits experienced by patients with lesions centered in or involving the TPJ area
Object-centred neglect: Simulation with head-centred coding based on Gaussian gaze-dependent units
No full textRight brain damaged patients affected by contralesional object-centred neglect are able to process all objects around them but systematically omit the left part of these objects. We show that pure object-centred neglect can be simulated by a basis function neural network in which the activity of units allowing head-centred coding of space is based on the activity of gaze-dependent units with no lateral gradient of preferred eye positions along the horizontal space. This type of network simulates complete dissociation between object-centred and egocentric neglect, as observed in patients' copies of multi-item drawings. Based on these results and available neurophysiological, clinical and brain imaging data, it is proposed that disruption of a cerebral network including dorsal occipital and parietal areas and the supplementary eye fields could be the main cause of object-centred neglect. (c) 2007 Elsevier Ltd. All rights reserved
Influence of figure-ground contrast on the implicit and explicit processing of line drawings in patients with left unilateral neglect.
No full textGravitational inputs modulate visuospatial neglect
No full textRight brain-damaged patients with left visuospatial
neglect were required to bisect a line placed in
front of them in two different body positions (upright
and supine) and two different light conditions (light and
dark). The neglect patients, unlike right brain-damaged
patients without neglect, strongly reduced their rightward
directional error in the supine compared with the upright
position. No systematic changes were produced by the
light-dark manipulation. The present result cannot be explained
with an attentional interpretation of hemispatial
neglect. We suggest that the present data provide futher
evidence that hemineglect is the consequence of a mismatch
between different afferent information integrated
into an egocentric space representation. According to this
model, the presence of a lateralized brain lesion produces
asymmetries in some intermediate spatial representations
(eye-head, head-trunk, body-environment) but not in the
retinotopic one. Any experimental manipulation that reduces
the asymmetry of the intermediate representation
such as the reduction of gravitational inputs may improve
the dynamic integration of the egocentric coordinates
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