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Peduncular-like Hallucinosis in the Absence of Midbrain or Thalamic Damage

André Zacharia, Asaid Khateb and Jean-Marie Annoni

An 87 year-old man was admitted for Peduncular hallucinosis (PH) characterized by acute vivid, continuous, complex visual and auditory hallucinations, which were triggered by fixation on a blank wall. The MRI revealed a subacute left parietal stroke. The symptoms disappeared after six weeks. An fMRI experiment, using periods of visual stimulation (checkerboard, VS) alternating with a hallucinosis-inducing condition (blank screen, PH) revealed that PH relative to VS elicited a complex pattern of activation involving the posterior cingulate cortex, the SMA, the left superior temporal gyrus and inferior parietal lobule. This is, to our knowledge, the first observation which indicated that PH-like could occur following cortical lesions. Moreover, fMRI results suggested that the internally-generated vivid and complex scenes in the patient’s brain were subtended by large associative neural networks that did not necessarily implicate the midbrain.