Visual hallucinations

Acute right opercular stroke-associated polyopic heautoscopy and hallucinations caused by disconnection to the inferior parietal lobule through the superior longitudinal fasciculus III: A single case study

Illusory neuropsychiatric symptoms such as hallucinations or the feeling of a presence (FOP) can occur in diffuse brain lesion or dysfunction, in psychiatric diseases as well as in healthy individuals. Their occurrence due to focal brain lesions is rare, most probably due to underreporting, which limits progress in understanding their underlying mechanisms and anatomical determinants. In this single case study, an 86-year-old patient experienced, in the context of an acute right central opercular ischemic stroke, visual hallucinatory symptoms (including palinopsia), differently lateralized auditory hallucinations and FOP. This unusual clinical constellation could be precisely documented and illustrated while still present, allowing a realistic and immersive visual experience validated by the patient. The acute stroke appeared to be their most plausible cause (after exclusion of other etiologies). Furthermore, accurate analysis of tractographic data suggested that disruption in the posterior bundle of the superior longitudinal fasciculus connecting the stroke lesion to the inferior parietal lobule was the anatomical substrate explaining the FOP and, indirectly, also hallucinations through whiter matter involvement, in coherence with existing literature. We could finally elaborate on symptoms taxonomy and phenomenology (e.g., polyopic heautoscopy, hallucinatory FOP, etc), and on patient's remarkable distancing from them (with some therapeutic implications supported by plausibly engaged mechanisms). This case not only authentically enriched the description of such rare combination of heterogenous illusory symptoms through this novel visualization-based reporting approach, but disclosed an unrevealed anatomo-clinical link relating all of them to the acute stroke lesion through an association fiber, thereby contributing to the understanding of these intriguing symptoms and their determinants.

Neural patterns of conscious visual awareness in the Riddoch syndrome

The Riddoch syndrome is one in which patients blinded by lesions to their primary visual cortex can consciously perceive visual motion in their blind field, an ability that correlates with activity in motion area V5. Our assessment of the characteristics of this syndrome in patient ST, using multimodal MRI, showed that: 1. ST's V5 is intact, receives direct subcortical input, and decodable neural patterns emerge in it only during the conscious perception of visual motion; 2. moving stimuli activate medial visual areas but, unless associated with decodable V5 activity, they remain unperceived; 3. ST's high confidence ratings when discriminating motion at chance levels, is associated with inferior frontal gyrus activity. Finally, we report that ST's Riddoch Syndrome results in hallucinatory motion with hippocampal activity as a correlate. Our results shed new light on perceptual experiences associated with this syndrome and on the neural determinants of conscious visual experience.