Recovery from auditory and visual neglect after optokinetic stimulation with pursuit eye movements--transient modulation and enduring treatment effects.

Optokinetic stimulation (OKS) modulates many facets of the neglect syndrome. This sensory stimulation technique is known to activate multiple brain regions (temporo-parietal cortex, basal ganglia, brain stem, cerebellum) some of which are involved in auditory and visual space coding. Here, we evaluated whether OKS modulates auditory neglect transiently and induces a sustained effect (Study 1), and whether repetitive OKS permanently recovers auditory neglect (Study 2). In Study 1, 20 patients with visuospatial neglect and auditory neglect in an auditory midline task following rightsided stroke were randomly allocated to an experimental and a control group matched for neglect severity and socio-demographic factors. Both groups showed a stable, pathological shift of their auditory subjective median plane (ASMP) in front space to the right side. During leftward OKS the experimental group showed a complete normalization of the shift of the ASMP, which endured until 30 min poststimulation, and returned almost to baseline values 24h after OKS. In contrast, the control group who viewed the identical but static dot pattern, showed neither change in their ASMP during this condition, nor any significant change at 30 min or 24h poststimulation. In Study 2, we show in two samples of neglect patients (N = 3 each) that repetitive leftward OKS with smooth pursuit eye movements as a therapy induces lasting improvements in auditory (the ASMP) and visual neglect while visual scanning therapy yielded no measurable effects on auditory and significantly smaller effects on visual neglect. In conclusion, the experiments show that a single session of OKS induces rapid though transient recovery from auditory neglect including a sustained effect after termination of stimulation, while repetitive OKS therapy yields enduring and multimodal recovery from auditory and visual neglect. OKS therapy with pursuit eye movements therefore represents a multimodally effective and easily applicable technique for the treatment of auditory and visual neglect.

Multimodal and multispatial deficits of verticality perception in hemispatial neglect.

Recent evidence suggests that patients with left-sided visuospatial neglect often show deviations in their visual and haptic perception of verticality in the frontal and sagittal plane. However, little is known about the multimodality of these impairments and the relationship between deviations in the frontal and the sagittal plane. Moreover, no previous study has combined investigations of verticality judgments in both modalities and both spatial planes within the same sample of subjects using the same apparatus. Thus, the aim of the present study was to investigate both subjective visual vertical (SVV) and subjective haptic vertical (SHV) judgments in the frontal and the sagittal plane in right-brain-damaged patients with visuospatial neglect (n=16), right-brain-damaged patients without neglect (n=18) and age-matched healthy individuals (n=16) using the same testing device for all tasks. This allowed for direct comparisons of visual vs. haptic and frontal vs. sagittal verticality judgments. Neglect patients showed significant counterclockwise tilts in their SVV and SHV judgments in the frontal plane as well as marked backward (upper end of the rod towards the observer) tilts in the sagittal plane. In contrast, right-brain-damaged patients without neglect and healthy individuals showed no marked deviations in the frontal plane, but small forward (upper end of the rod away from the observer) tilts in the sagittal plane. Moreover, neglect patients showed significantly higher unsigned errors in all tasks. These results demonstrate multimodal and multispatial deficits in the judgment of verticality in patients with visuospatial neglect which are most likely due to an altered representation of verticality caused by lesions of brain areas related to multisensory integration and space representation in the right temporo-parietal cortex.

Contrasting spatial hearing deficits in hemianopia and spatial neglect.

Spatial hearing deficits have been described in widely differing pathologies, including bilateral temporal or unilateral parietal lesions, hemispherectomy, spatial neglect and right-sided cortical lesions without neglect. However, the topography of spatial hearing deficits after cortical lesions is only poorly understood, unlike that of vision and touch. We investigated the auditory subjective straight ahead (SSA) with a new technique of binaural sound source simulation using broad-band single pulses which were filtered with head-related transfer functions and delivered with a 5 degree resolution over headphones in front space. Normal subjects showed quite accurate judgments of the SSA, with a small but significant shift to the left of centre (-1.7 degrees) in the horizontal plane. Hemineglect without a scotoma, produced a large ipsilesional deviation of the auditory SSA (+22 degrees), while two hemianopic subjects, both without neglect, showed the opposite deviation of their perceived auditory SSA towards their contralesional, blind hemifield (+10 vs -28 degrees). Two control patients with unilateral lesions, both without neglect and without hemianopia, produced normal judgments of their auditory SSA (-3.0 degrees, +3.8 degrees). These results suggest at least two contrasting influences on directional spatial hearing after unilateral cortical lesions: hemianopia vs hemispatial neglect. The results are interpreted in favour of multisensory convergence of visual and auditory information in directional spatial hearing.