Peduncular hallucinosis (PH), or Lhermitte's peduncular hallucinosis, is a rare neurological disorder, which causes vivid visual hallucinations that typically occur in dark environments, and last for several minutes. Unlike some other kinds of hallucinations, those that patients with PT experience are very realistic, and often involve people and environments that are familiar to the affected individuals. Because the content of the hallucinations is never exceptionally bizarre, patients can rarely distinguish between the hallucinations and reality.
In 1922, the French neurologist Jean Lhermitte documented the case of a patient who was experiencing visual hallucinations that were suggestive of localized damage to the midbrain and pons. After other similar case studies were published, this syndrome was labeled "peduncular hallucinosis."
The accumulation of additional cases by Lhermitte and by others influenced academic medical debate about hallucinations and about behavioral neurology.
Lhermitte provided a full account of his work in this area in his book "Les hallucinations: clinique et physiopathologie," which was published in Paris in 1951 by Doin publishing.
Contemporary researchers, with access to new technologies in medical brain imaging, have confirmed the brain localization of these unusual hallucinations.