Passive auditory stimulation improves vision in hemianopia.

UNLABELLED: 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.

Distortion of auditory space in hemianopia.

Sound localization was investigated in patients with homonymous hemianopia, a visual field defect characterized by a loss of vision in one hemifield that is caused by unilateral brain lesions involving the visual cortex or its afferents. The primary aim was to clarify whether or not the known distortion of visual space in hemianopia results in processes of long-term cross-modal spatial adaptation, thus eventually inducing related alterations in auditory space perception. For this purpose, patients were tested by using tasks of either head pointing or manual pointing to acoustic targets in the azimuthal plane, under anechoic conditions in total darkness. The results obtained with both tasks consistently indicated slight, but significant, systematic errors compared with normal controls. In particular, the errors found can be interpreted by both rotation and compression of auditory space toward the anopic side. These findings can be explained by a visual miscalibration of the auditory space, as has been analogously demonstrated in studies on normal-sighted subjects after exposure to consistent auditory-visual disparity, for example by wearing prism lenses. The precision in sound localization of hemianopic patients was generally reduced across both hemispaces. Taken together, one may conclude that processes of cross-modal spatial adaptation, but not those of compensatory plasticity, occurred in patients with hemianopia.

Perception of stationary and moving sound following unilateral cortectomy.

The perception of motion is an essential prerequisite to responding adequately to the dynamic aspects of sensory information in the environment. The neural substrates of auditory motion processing are, at present, still a matter of debate. It has been hypothesized that motion information is, as in the visual system, processed separately from other aspects of auditory information, such as stationary location. Here we report data on auditory perception of stationary and motion stimuli from a subject with right-sided resection of the anterior temporal-lobe region including medial aspects of Heschl's gyrus, and from three subjects with unilateral (right-sided or left-sided) hemispherectomy. All these subjects had undergone cortectomy decades earlier. The subjects with hemispherectomy were completely unable to perceive auditory motion, but showed slight to moderate deficits in judging stationary location. The subject with temporal lobectomy exhibited quite similar stationary auditory deficits as found in the subjects with hemispherectomy, but was completely normal in judging auditory motion. Thus, there was a clear dissociation of the effects of unilateral temporal lobectomy and hemispherectomy on auditory motion perception. Collectively, these findings suggest that the unilateral anterior temporal-lobe region plays a significant role in the analysis of stationary, but not moving, sound. One may assume that the cortical "motion network" is distinct from the "stationary network", and is located either in the most posterior aspects of temporal lobe, or in non-temporal, most likely parietal, areas.

An fMRI study of theory of mind in schizophrenic patients with "passivity" symptoms.

Several studies have shown that patients with schizophrenia underactivate brain regions involved in theory of mind relative to controls during functional brain imaging. However, in most studies the samples were fairly heterogeneous in terms of clinical symptomatology. We examined a group of nine patients with first episode or recurrent episodes, who clinically presented with predominant "passivity" symptoms such as third-person auditory hallucinations or delusion of control, using a cartoon-based theory of mind task and compared activation patterns with a group of 13 healthy controls. All patients responded well to antipsychotic treatment and were only mildly symptomatic at the time of testing. The patient group showed significantly less activation of the right anterior cingulate cortex (ACC) and right insula compared with controls, but greater activation in dorsal areas of the medial prefrontal cortex, right temporal areas and left temporo-parietal junction. Patients with schizophrenia with predominant "passivity" symptoms and good response to antipsychotic treatment show a markedly diverging pattern of brain activation during theory of mind task performance compared with healthy controls. These findings suggest abnormal activation of those brain areas involved in the evaluation of self-reference during mental state attribution.