640 research outputs found

    The prognosis of allocentric and egocentric neglect : evidence from clinical scans

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    We contrasted the neuroanatomical substrates of sub-acute and chronic visuospatial deficits associated with different aspects of unilateral neglect using computed tomography scans acquired as part of routine clinical diagnosis. Voxel-wise statistical analyses were conducted on a group of 160 stroke patients scanned at a sub-acute stage. Lesion-deficit relationships were assessed across the whole brain, separately for grey and white matter. We assessed lesions that were associated with behavioural performance (i) at a sub-acute stage (within 3 months of the stroke) and (ii) at a chronic stage (after 9 months post stroke). Allocentric and egocentric neglect symptoms at the sub-acute stage were associated with lesions to dissociated regions within the frontal lobe, amongst other regions. However the frontal lesions were not associated with neglect at the chronic stage. On the other hand, lesions in the angular gyrus were associated with persistent allocentric neglect. In contrast, lesions within the superior temporal gyrus extending into the supramarginal gyrus, as well as lesions within the basal ganglia and insula, were associated with persistent egocentric neglect. Damage within the temporo-parietal junction was associated with both types of neglect at the sub-acute stage and 9 months later. Furthermore, white matter disconnections resulting from damage along the superior longitudinal fasciculus were associated with both types of neglect and critically related to both sub-acute and chronic deficits. Finally, there was a significant difference in the lesion volume between patients who recovered from neglect and patients with chronic deficits. The findings presented provide evidence that (i) the lesion location and lesion size can be used to successfully predict the outcome of neglect based on clinical CT scans, (ii) lesion location alone can serve as a critical predictor for persistent neglect symptoms, (iii) wide spread lesions are associated with neglect symptoms at the sub-acute stage but only some of these are critical for predicting whether neglect will become a chronic disorder and (iv) the severity of behavioural symptoms can be a useful predictor of recovery in the absence of neuroimaging findings on clinical scans. We discuss the implications for understanding the symptoms of the neglect syndrome, the recovery of function and the use of clinical scans to predict outcome

    A Behavioral Analysis of Spatial Neglect and its Recovery After Stroke

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    In a longitudinal study of recovery of left neglect following stroke using reaction time computerized assessment, we find that lateralized spatial deficits of attention and perception to be more severe than disturbance of action. Perceptual-attention deficits also show the most variability in the course of recovery, making them prime candidates for intervention. In an anatomical analysis of MRI findings, ventral frontal cortex damage was correlated with the most severe neglect, reflecting impaired fronto-parietal communication

    The role of the cerebellum in unconsciuos and conscious processing of emotions: a review

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    Studies from the past three decades have demonstrated that there is cerebellar involvement in the emotional domain. Emotional processing in humans requires both unconscious and conscious mechanisms. A significant amount of evidence indicates that the cerebellum is one of the cerebral structures that subserve emotional processing, although conflicting data have been reported on its function in unconscious and conscious mechanisms. This review discusses the available clinical, neuroimaging and neurophysiological data on this issue. We also propose a model in which the cerebellum acts as a mediator between the internal state and external environment for the unconscious and conscious levels of emotional processing

    Is there a critical lesion site for unilateral spatial neglect? A meta-analysis using activation likelihood estimation

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    The critical lesion site responsible for the syndrome of unilateral spatial neglect has been debated for more than a decade. Here we performed an activation likelihood estimation (ALE) to provide for the first time an objective quantitative index of the consistency of lesion sites across anatomical group studies of spatial neglect. The analysis revealed several distinct regions in which damage has consistently been associated with spatial neglect symptoms. Lesioned clusters were located in several cortical and subcortical regions of the right hemisphere, including the middle and superior temporal gyrus, inferior parietal lobule, intraparietal sulcus, precuneus, middle occipital gyrus, caudate nucleus, and posterior insula, as well as in the white matter pathway corresponding to the posterior part of the superior longitudinal fasciculus. Further analyses suggested that separate lesion sites are associated with impairments in different behavioral tests, such as line bisection and target cancellation. Similarly, specific subcomponents of the heterogeneous neglect syndrome, such as extinction and allocentric and personal neglect, are associated with distinct lesion sites. Future progress in delineating the neuropathological correlates of spatial neglect will depend upon the development of more refined measures of perceptual and cognitive functions than those currently available in the clinical setting

    The functional role of dreaming in emotional processes

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    Dream experience (DE) represents a fascinating condition linked to emotional processes and the human inner world. Although the overlap between REM sleep and dreaming has been overcome, several studies point out that emotional and perceptually vivid contents are more frequent when reported upon awakenings from this sleep stage. Actually, it is well-known that REM sleep plays a pivotal role in the processing of salient and emotional waking-life experiences, strongly contributing to the emotional memory consolidation. In this vein, we highlighted that, to some extent, neuroimaging studies showed that the processes that regulate dreaming and emotional salience in sleep mentation share similar neural substrates of those controlling emotions during wakefulness. Furthermore, the research on EEG correlates of the presence/absence of DE and the results on EEG pattern related to the incorporated memories converged to assign a crucial role of REM theta oscillations in emotional re-processing. In particular, the theta activity is involved in memory processes during REM sleep as well as during the waking state, in line with the continuity hypothesis. Also, the gamma activity seems to be related to emotional processes and dream recall as well as to lucid dreams. Interestingly, similar EEG correlates of DE have been found in clinical samples when nightmares or dreams occur. Research on clinical samples revealed that promoting the rehearsal of frightening contents aimed to change them is a promising method to treat nightmares, and that lucid dreams are associated with an attenuation of nightmares. In this view, DE can defuse emotional traumatic memories when the emotional regulation and the fear extinction mechanisms are compromised by traumatic and frightening events. Finally, dreams could represent a sort of simulation of reality, providing the possibility to create a new scenario with emotional mastery elements to cope with dysphoric items included in nightmares. In addition, it could be hypothesized that the insertion of bizarre items besides traumatic memories might be functional to “impoverish” the negative charge of the experiences

    Human Amygdala in Sensory and Attentional Unawareness: Neural Pathways and Behavioural Outcomes

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    One of the neural structures more often implicated in the processing of emotional signals in the absence of visual awareness is the amygdala. In this chapter, we review current evidence from human neuroscience in healthy and brain-damaged patients on the role of amygdala during non-conscious (visual) perception of emotional stimuli. Nevertheless, there is as of yet no consensus on the limits and conditions that affect the extent of amygdala’s response without focused attention or awareness. We propose to distinguish between attentional unawareness, a condition wherein the stimulus is potentially accessible to enter visual awareness but fails to do so because attention is diverted, and sensory unawareness, in which the stimulus fails to enter awareness because its normal processing in the visual cortex is suppressed. Within this conceptual framework, some of the apparently contradictory findings seem to gain new coherence and converge on the role of the amygdala in supporting different types of non-conscious emotion processing. Amygdala responses in the absence of awareness are linked to different functional mechanisms and are driven by more complex neural networks than commonly assumed. Acknowledging this complexity can be helpful to foster new studies on amygdala functions without awareness and their impact on human behaviour

    Structural connectivity associated with the sense of body ownership: a diffusion tensor imaging and disconnection study in patients with bodily awareness disorder

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    The brain mechanisms underlying the emergence of a normal sense of body ownership can be investigated starting from pathological conditions in which body awareness is selectively impaired. Here, we focused on pathological embodiment, a body ownership disturbance observed in brain-damaged patients who misidentify other people's limbs as their own. We investigated whether such body ownership disturbance can be classified as a disconnection syndrome, using three different approaches based on diffusion tensor imaging: (i) reconstruction of disconnectome maps in a large sample (N = 70) of stroke patients with and without pathological embodiment; (ii) probabilistic tractography, performed on the age-matched healthy controls (N = 16), to trace cortical connections potentially interrupted in patients with pathological embodiment and spared in patients without this pathological condition; (iii) probabilistic 'in vivo' tractography on two patients without and one patient with pathological embodiment. The converging results revealed the arcuate fasciculus and the third branch of the superior longitudinal fasciculus as mainly involved fibre tracts in patients showing pathological embodiment, suggesting that this condition could be related to the disconnection between frontal, parietal and temporal areas. This evidence raises the possibility of a ventral self-body recognition route including regions where visual (computed in occipito-temporal areas) and sensorimotor (stored in premotor and parietal areas) body representations are integrated, giving rise to a normal sense of body ownership

    Normal and impaired reflexive orienting of attention after central nonpredictive cues

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    Recent studies suggest that stimuli with directional meaning can trigger lateral shifts of visuospatial attention when centrally presented as noninformative cues. We investigated covert orienting in healthy participants and in a group of 17 right braindamaged patients (9 with hemispatial neglect) comparing arrows, eye gaze, and digits as central nonpredictive cues in a detection task. Orienting effects elicited by arrows and eye gaze were overall consistent in healthy participants and in right brain-damaged patients, whereas digit cues were ineffective. Moreover, patients with neglect showed, at the shortest delay between cue and target, a disengage deficit for arrow cueing whose magnitude was predicted by neglect severity. We conclude that the peculiar form of attentional orienting triggered by the directional meaning of arrow cues presents some features previously thought to characterize only the stimulus-driven (exogenous) orienting to noninformative peripheral cues

    Anatomical correlates for visual extinction - a fMRI study

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    Hintergrund: Gesunde Erwachsene können nur eine begrenzte Menge an Informationen verarbeiten. Bei Patienten mit visueller Extinktion, einer Erkrankung die nach rechtshemisphĂ€rischen SchlaganfĂ€llen auftreten kann, ist diese natĂŒrliche Limitierung gesteigert und resultiert darin, dass Patienten bei PrĂ€sentation beidseitiger Stimuli den kontralĂ€sionellen Reiz auslöschen. Ziel dieser Studie war es, Bereiche des Gehirns zu identifizieren, die fĂŒr die Verarbeitung multipler visueller Reize verantwortlich sind. Unter BerĂŒcksichtigung der “top-down-” und bottom-up”-Aufmerksamkeitsmodelle und der Ergebnisse von TMS- (transcranielle Magnetstimulation) und fMRT- (funktionelle Kernspintomographie) Studien, wurde die Hypothese gestellt, dass dem rechtshemisphĂ€rischen intraparietalen Sulcus (IPS) eine wichtige Rolle bei der Aufmerksamkeitslenkung auf bilaterale Reize und der temporoparietale junction (TPJ) eine wichtige Rolle bei der Erkennung dieser bilateralen Reize zukommt. Methoden: 24 Probanden nahmen an einem fMRT-Experiment teil welches in fĂŒnf Einheiten mit je 400 VersuchsdurchgĂ€ngen gegliedert war. Ein Versuchsdurchgang bestand aus einem neutralen oder informativen Hinweisreiz (HR) welcher in Richtung eines rechtsseitigen, linksseitigen oder beidseitigen Zielkastens wies. Nach einem variablen Zeitintervall erschienen im jeweils angekĂŒndigtem Zielkasten ein Zielreiz (ZR) oder ein Ablenkreiz (AR). Augenbewegungen und Reaktionszeiten wurden aufgezeichnet. Statistische Auswertung der Bildgebungsdaten und die Erstellung der nachfolgend genannten Kontraste erfolgte mittels SPM8 (Statistical parametric mapping). Kontrastmodelle waren: a) unilateraler HR links vs. bilateraler HR, b) unilateraler HR rechts vs. bilateraler HR, c) unilateraler ZR links vs. bilateraler ZR, d) unilateraler HR rechts vs. bilateraler HR. Durch Überlappung der einzelnen Kontraste (sog. Konjunktionsbilder) wurden diejenigen Voxel sichtbar, welche stĂ€rker auf PrĂ€sentation bilateraler HRs und ZRs reagiert haben als auf die jeweiligen unilateralen Reize. Ergebnisse: In 97,6 ± 2,5% der Versuchszeit fixierten die Probanden einen zentralen Fixationspunkt. Reaktionszeiten (RTs) fĂŒr ZR die einem informativen HR folgten, waren signifikant schneller. Die Detektion bilateraler ZR resultierte in lĂ€ngeren RTs als die Detektion einzelner ZR. Das Konjunktionsbild der HR-Bedingung zeigte eine Überlappung im rechtshemisphĂ€rischem inferiorem frontalen Gyrus (IFG) und das der ZR-Bedingung im rechtshemisphĂ€rischem IPS und Gyrus cinguli (CG)/ superiorem frontalen Gyrus (SFG). Diskussion: Die schnelleren RTs fĂŒr erwartete ZR deuten darauf hin, dass die Probanden aufmerksam waren und die HR als Informationsquelle nutzten. Die langsameren RTs bei der Detektion bilateraler ZR könnten durch eine grĂ¶ĂŸere kognitive Herausforderung bedingt sein. Die Bildgebungsdaten fĂŒr die Bedingungen HR und ZR zeigten Aktivierungen in den okzipitalen Regionen korrespondierend zu den bekannten Arealen der Sehbahn nach rechts- und linksseitiger Stimulation und resultierend aus einer durch den HR modulierten Aktivierung in den entsprechenden visuellen Cortices. Die fMRT Ergebnisse der Konjunktionsbilder [bilateral vs unilateraler HR links + bilateraler vs unilateraler HR rechts] und [bilateraler vs ZR links + bilateraler vs ZR rechts] zeigten insgesamt mehr Aktivierungen in der rechten GehirnhemisphĂ€re. Diese Ergebnisse stimmen mit bekannten LĂ€sionsstudien ĂŒberein und unterstĂŒtzen die Annahme einer rechtshemisphĂ€rischen Dominanz fĂŒr rĂ€umliche Aufmerksamkeit. Bilaterale HRs erzeugten Aktivierungen im rechtshemisphĂ€rischen IFG. Als Teil des ventroparietalen Netzwerkes ist war diese Aktivierung unerwartet, jedoch in Studien mit Ă€hnlichem Versuchsaufbau bereits vorbeschrieben. Anders als erwartet kam es im Bereich des IPS nur in der ZR-Bedingung zu Aktivierungen und nicht in der HR-Bedingung. Diese Studie ist die erste Bildgebungsstudie welche IPS-Aktivierungen wĂ€hrend dem Erkennen beidseitiger ZR zeigt. Diese Ergebnisse stehen im Einklang mit Ergebnissen von frĂŒheren TMS-Studien. Die Rolle des CG/SFG beim Erkennen beidseitiger ZR ist bis dato unklar und bedarf weiteren Untersuchungen. Bislang waren diese Hirnareale v.a. mit psychiatrischen Funktionsstörungen aber auch mit zielorientiertem Verhalten assoziiert. Schlussfolgerung Aktivierungen im IPS in der HR-Bedingung und TPJ-Aktivierung in der ZR-Bedingung konnten nicht nachgewiesen werden. Stattdessen konnten Aktivierungen im IPS in der ZR-Bedingung demonstriert werden, sodass dennoch von einer wichtigen Rolle des IPS beim Erkennen multipler Reize auszugehen ist. Unsere Ergebnisse weisen daraufhin, dass der rechtshemisphĂ€rische IFG eine wichtige Aufgabe bei der Lenkung von Aufmerksamkeit auf beidseitige und erwartete ZR ĂŒbernimmt. Die fehlende TPJ-Aktivierung ist möglicherweise durch den Versuchsaufbau erklĂ€rt

    Hemispatial neglect and deficits of verticality perception after stroke - neuropsychological results and modulation via galvanic vestibular stimulation

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    Hemispatial neglect is a multimodal syndrome that often follows unilateral right-brain damage. Patients with hemispatial neglect fail to notice or respond to sensory stimuli presented in the contralesional hemispace, which is not caused by primary motor or sensory deficits. Associated disorders often co-occurring with hemispatial neglect are deficits of verticality perception. Patients with those deficits show significant deviations in their subjective visual or haptic vertical away from the objective physical vertical when being asked to indicate whether a stepwise rotatable rod in the frontal plane is vertical, either by seeing the rod (visual modality) or by touching it when blindfolded (haptic modality). Both, hemispatial neglect and disorders of verticality perception are very frequent and strongly related to substantial impairments in daily life. Thus, research on the subserving mechanisms and potential treatment methods is of high significance. Four studies were conducted, first addressing the potential benefits and risks of a new treatment method for patients with hemispatial neglect, and second investigating the multimodality of disorders of verticality perception and their occurrence in different spatial planes (frontal, sagittal). Study 1 to 3 of the present doctoral thesis focus on a potential new treatment technique of hemispatial neglect and related disorders, the so-called galvanic vestibular stimulation (GVS). GVS uses weak direct current delivered via electrodes placed on the mastoids behind the ears. The direct current leads to polarization effects of the vestibular nerves and activations of multisensory vestibular brain areas, which are often lesioned in patients with hemispatial neglect and deficits of verticality perception. In order to obtain a broad overview over the technique of GVS and the available evidence of its potential to modulate different neuropsychological phenomena, in Study 1 the scientific literature on GVS and the related technique of transcranial direct current stimulation (tDCS; electrodes are attached to the skull over the target cortical area) in the field of neuropsychology was reviewed. Both GVS and tDCS over the parietal cortex were proven to be able to modulate neglect and related disorders, with little evidence showing GVS-induced modulation of deficits of verticality perception. Study 2 was concerned with the frequency and intensity of adverse effects during and after GVS in persons with stroke and healthy individuals, recorded via a questionnaire. The results indicate only very few and slight adverse effects like mild itching and tingling underneath the electrodes during and after stimulation in both groups. Hence, GVS was shown to be a suitable and easily applicable technique for modulation with only minimal adverse effects. In Study 3, the question was addressed whether GVS modulates a frequent neglect phenomenon, namely the rightward error in horizontal line bisection. GVS significantly decreased the rightward line bisection error during stimulation in right-brain-damaged patients with but not without neglect in contrast with sham stimulation. Right-cathodal GVS was more effective than left-cathodal GVS. Finally, in Study 4 the subjective verticality judgments in two modalities (visual, haptic) and two spatial planes (frontal, sagittal) of right-brain-damaged patients with neglect, right-brain-damaged patients without neglect and age-matched healthy individuals were investigated using a novel testing device for all these tasks. We observed greater unsigned errors and significant perceptual tilts in the verticality judgments of right-brain-damaged patients with neglect in contrast to the other two groups. Tilts of the neglect patients were directed counterclockwise in the roll plane, and towards the observer in the sagittal plane for both modalities. In summary, the studies presented in this work suggest that GVS is a promising treatment method which is able to modulate neglect phenomena and related disorders and is furthermore well-tolerated by persons with stroke and healthy individuals. The beneficial effects of GVS are most likely induced by activation of surviving remnants of the otherwise lesioned multimodal vestibular brain areas in neglect patients, thereby re-calibrating their disturbed spatial representations. Furthermore the present thesis shows that deficits of verticality perception in neglect patients are multimodal and multispatial in nature. These impairments are presumably due to lesions of temporoparietal cortical regions involved in multisensory integration which leads to a disturbed representation of the vertical.Hemispatialer Neglect ist ein multimodales Syndrom, das hĂ€ufig nach unilateralen rechtshemisphĂ€rischen HirnschĂ€digungen auftritt. Patienten mit hemispatialem Neglect beachten keine oder reagieren nicht auf sensorische Reize, die im kontralĂ€sionalen Halbraum auftreten. Assoziierte Störungen, die hĂ€ufig das Neglect-Syndrom begleiten, sind Störungen der Vertikalenwahrnehmung. Davon betroffene Patienten zeigen signifikante Abweichungen von der physikalischen Vertikalen in ihrer subjektiven visuellen oder haptischen Vertikalen. Hierbei mĂŒssen die Patienten angeben, wann ein in der Frontalebene schrittweise drehbarer Stab vertikal ist (visuelle ModalitĂ€t) oder den Stab mit verbunden Augen vertikal ausrichten (haptische ModalitĂ€t). Beide Störungsbilder kommen hĂ€ufig vor und gehen mit betrĂ€chtlichen EinschrĂ€nkungen im Alltagsleben einher. Aus diesem Grund ist die Erforschung der zugrundeliegenden Mechanismen und möglicher Behandlungsmethoden der Störungen von hoher Relevanz. Im Rahmen dieser Arbeit wurden vier Studien durchgefĂŒhrt, um einerseits den potentiellen Nutzen und die Risiken einer neuen Behandlungsmethode fĂŒr hemispatialen Neglect zu erfassen, und andererseits das Vorkommen von Störungen der Vertikalenwahrnehmung in verschiedenen ModalitĂ€ten und verschiedenen Raumebenen (frontal, sagittal) zu untersuchen. Studien 1 bis 3 der vorliegenden Dissertation widmen sich einer neuen potentiellen Behandlungsmethode von Patienten mit hemispatialem Neglect und verwandten Störungen, der sogenannten Galvanisch VestibulĂ€ren Stimulation (GVS). Hierbei wird Gleichstrom geringer IntensitĂ€t mittels Elektroden appliziert, welche auf den Mastoiden hinter den Ohren platziert werden. Dies aktiviert multisensorische vestibulĂ€re Hirnareale, welche hĂ€ufig bei Patienten mit hemispatialem Neglect und Störungen der Vertikalenwahrnehmung geschĂ€digt sind. Um einen breiten Überblick ĂŒber die Methode der GVS und der vorhandenen Untersuchungen zur Modulation von neuropsychologischen Funktionen mittels dieser Methode zu erhalten, wurde in Studie 1 ein LiteraturĂŒberblick ĂŒber die wissenschaftlichen Veröffentlichungen zur GVS und der verwandten Technik der Transkraniellen Gleichtstromstimulation (tDCS; Elektroden werden auf dem SchĂ€del, ĂŒber dem zu stimulierenden Kortexbereich, platziert) im Bereich der Neuropsychologie gegeben. Hierbei stellte sich heraus, dass beide Methoden, GVS und tDCS ĂŒber dem Parietalkortex, in der Lage sind, Neglect und verwandte Störungen zu modulieren. In Studie 2 wurde die HĂ€ufigkeit und IntensitĂ€t von Nebenwirkungen wĂ€hrend und nach GVS bei Personen mit Schlaganfall und gesunden Individuen anhand eines Fragebogens erfasst. Die Befunde zeigen, dass GVS nur zu wenigen und leichten Nebenwirkungen, wie leichtes Jucken und Kribbeln der Haut unter den Elektroden, wĂ€hrend und nach der Stimulation in beiden Probandengruppen fĂŒhrte. In Studie 3 wurde untersucht, ob GVS ein hĂ€ufig vorkommendes NeglectphĂ€nomen, nĂ€mlich die Rechtsabweichung im horizontalen Linienhalbieren, moduliert. GVS verringerte wĂ€hrend der Stimulation die Rechtsabweichung von Patienten mit rechtshemisphĂ€rischen HirnschĂ€digungen mit Neglect, nicht aber die von rechtshemisphĂ€risch geschĂ€digten Patienten ohne Neglect. Rechts-kathodale GVS war hierbei effektiver als links-kathodale GVS. Schließlich wurde in Studie 4 die Beurteilung der Vertikalen in zwei ModalitĂ€ten (visuell, haptisch) und zwei Raumebenen (frontal, sagittal) von rechtshemisphĂ€risch geschĂ€digten Patienten mit Neglect, ohne Neglect, sowie von altersentsprechenden gesunden Individuen erfasst. Dabei wurde ein neues UntersuchungsgerĂ€t eingesetzt, welches fĂŒr alle Aufgaben verwendet wurde. Wir beobachteten grĂ¶ĂŸere ungerichtete Fehler und signifikante Verkippungen in den VertikalitĂ€ts-Urteilen von rechtshemisphĂ€risch geschĂ€digten Patienten mit Neglect im Vergleich zu den anderen beiden Probandengruppen. Die Abweichungen der Neglectpatienten waren in der Frontalebene gegen den Uhrzeigersinn gerichtet und zeigten in der Sagittalebene in Richtung des Beobachters. Dieses Muster wurde in beiden ModalitĂ€ten beobachtet. Zusammengefasst legen die hier dargestellten Studien nahe, dass GVS eine vielversprechende Methode zur Modulation von NeglectphĂ€nomenen und verwandten Störungen ist und darĂŒber hinaus gut vertragen wird. Die positiven Effekte von GVS bei Neglectpatienten basieren höchstwahrscheinlich auf der Aktivierung erhaltener Bereiche in ansonsten geschĂ€digten multisensorischen vestibulĂ€ren Hirnbereichen, wodurch gestörte rĂ€umliche ReprĂ€sentationen rekalibriert werden. DarĂŒber hinaus zeigt die vorliegende Dissertation, dass Störungen der Vertikalenwahrnehmung von Neglectpatienten multimodal sind und in verschiedenen Raumebenen auftreten. Diese Störungen sind vermutlich bedingt durch LĂ€sionen temporo-parietaler Kortexareale, welche an der multisensorischen Integration beteiligt sind und folglich zu gestörten ReprĂ€sentationen der Vertikalen fĂŒhren
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