Abstract
Techniques employed in rehabilitation of visual field disorders such as hemianopia are usually based on either visual or audio-visual stimulation and patients have to perform a training task. Here we present results from a completely different, novel approach that was based on passive unimodal auditory stimulation. Ten patients with either left or right-sided pure hemianopia (without neglect) received one hour of unilateral passive auditory stimulation on either their anopic or their intact side by application of repetitive trains of sound pulses emitted simultaneously via two loudspeakers. Immediately before and after passive auditory stimulation as well as after a period of recovery, patients completed a simple visual task requiring detection of light flashes presented along the horizontal plane in total darkness. The results showed that one-time passive auditory stimulation on the side of the blind, but not of the intact, hemifield of patients with hemianopia induced an improvement in visual detections by almost 100% within 30 min after passive auditory stimulation. This enhancement in performance was reversible and was reduced to baseline 1.5 h later. A non-significant trend of a shift of the visual field border toward the blind hemifield was obtained after passive auditory stimulation. These results are compatible with the view that passive auditory stimulation elicited some activation of the residual visual pathways, which are known to be multisensory and may also be sensitive to unimodal auditory stimuli as were used here.Trial Registration DRKS00003577
Highlights
In the mammalian brain, auditory and visual systems are closely interconnected
Posthoc comparisons, using paired t-tests, revealed that the mean percentage of correct detections obtained in the post-passive auditory stimulation (PAS) block after PAS on the anopic side (9.56%, SE 2.01) was significantly higher than those of both pre-PAS (5.17%, SE 2.03; t[9] = 4.29, p = 0.0020) and recovery (5.09%, SE 1.30; t[9] = 4.09, p = 0.0027), while the recovery results did not differ from the pre-PAS data (t[9] = 0.07, p = 0.95)
The majority of patients, but not all, showed a shift of the VF border toward the anopic hemifield in the post-PAS block, and in the recovery block the VF border was consistently shifted to the intact hemifield with reference to its position in the post-PAS block. doi:10.1371/journal.pone.0031603.g007. These results showed that one hour of PAS on the side of the blind, but not of the intact, hemifield of patients with HA induced an improvement in visual detections by almost 100% within 30 min after PAS
Summary
Single-neuron recordings in non-human species have demonstrated auditory-visual bisensory responses as well as effects of cross-modal integration in a multitude of subcortical and cortical regions These comprise the inferior and superior colliculi, the thalamus and frontal, temporal, insular, parietal, and occipital cortices which include the presumptive unimodal sensory areas. The functional integrity of the SC in HA may result in the retention of some residual visual functions (at a relatively low unconscious level without acknowledged awareness) in their anopic hemifield which has been referred to as blindsight [5,6,7,8,9,10] These residual abilities in HA have usually been proposed to rely on ‘‘residual’’ visual pathways that are independent of the damaged geniculostriate pathway to the primary occipital area (V1). Residual visual abilities in the anopic hemifield of HA patients can, in principle, rely on two types of residual fibers: (1) intact fibers of the extrastriate visual pathways and (2) surviving fibers in the partially damaged primary visual system
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