[Auditory hallucinations in lesions of the brain stem]

Since the publication by Jean Lhermitte in 1922 of his paper on hallucinosis, the peduncular type has been described as a purely visual phenomenon. However, limited brain stem lesions can give rise to analogous manifestations in the auditory field. Five cases of auditory hallucinosis are reviewed, the first four resulting from a lesion of tegmentum of pons responsible for contralateral hemi-anesthesia and homolateral facial palsy with paralysis of laterality. Central type hypoacusis and a severe disorder of localization of sounds revealed a lesion of trapezoid body. The fifth case resulted from a peduncular lesion in region supplied by superior cerebellar artery, the auditory deficit being related to a lesion of inferior corpus quadrigeminum. In one patient, the auditory hallucinosis was followed by a period of visual hallucinations and oneiric delusions. Both auditory and visual hallucinosis can be related to hypnagogic hallucinations. Dream mechanisms (the geniculo-occipital spikes system) escape from normal inhibitory control exerted by the raphe nuclei. Auditory deafferentation could predispose to auditory hallucinosis.