TY  - THES
T1  - Hemispatial neglect and deficits of verticality perception after stroke - neuropsychological results and modulation via galvanic vestibular stimulation
A1  - Utz,Kathrin Susanne
Y1  - 2012/01/12
N2  - 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.
KW  - Neglect
KW  - Neuropsychologie
KW  - Schlaganfall
KW  - Hirnstimulation
KW  - Raumwahrnehmung
CY  - Saarbrücken
PB  - Universitäts- und Landesbibliothek
AD  - Postfach 151141, 66041 Saarbrücken
UR  - http://scidok.sulb.uni-saarland.de/volltexte/2012/4550
ER  -