‘Distorteidolias' - Fantastic Perceptive Distortion

Abstract

The role of the thalamus in the pathogenesis of the visual and auditory hallucinations has been reported under the name of peduncular hallucinosis, usually with coexisting midbrain involvement. These hallucinations typically take the form of dreamy de novo productions (phanteidolias), less often that of transformations of perceptions into new items (such as seeing faces in clouds) called pareidolias. However, hallucinations taking the form of a complex distortion of perception is a different phenomenon, which to our knowledge has not been reported. We studied 2 patients with complex, ‘fantastic', perceptive distortion involving the visual and auditory systems after thalamic stroke limited to the region of the dorsomedial nucleus, sparing the intralaminar nuclei and the midbrain (explaining the lack of disorders of consciousness and confusional state). Our patients reported the modification of usual stimuli (face, body, voices) into unreal, fantastically distorted perceptions (monstrous change of shapes or sounds without appearance of new items). While the exact mechanism leading to such perceptive distortions remains unknown, a release phenomenon due to damage to the dorsomedial thalamus (probably affecting cholinergic system) responsible for a disinhibition of cortical function involved in familiarity of perception seems likely. We suggest that these hallucinations should be called ‘distorteidolias'.

Lesions to the mediodorsal thalamus, but not orbitofrontal cortex, enhance volatility beliefs linked to paranoia

“… 3 , 4 , 6 What is the role (if any) of MD in paranoia and psychosis? There are isolated cases where circumscribed lesions cause new-onset paranoia in humans 19 , 30 and frightening distortions of social stimuli, 31 but there are also more diffuse (often mnemonic) problems associated with MD damage, which can, as a result of impaired interpersonal behavior, lead indirectly to paranoia. Alternatively, genetic changes and the atrophy in frontotemporal dementia (FTD) are often quite specific to MD, 32 and psychotic symptoms (specifically paranoia) are common in FTD.…”