Peduncular hallucinosis (PH) is a rare neurological phenomenon that causes vivid visual hallucinations that typically occur in dark environments and last for several minutes. Unlike some other kinds of hallucinations, the hallucinations that patients with PH 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. Signs and symptoms The hallucinations are normally colorful, vivid images that occur during wakefulness, predominantly at night. Lilliputian hallucinations (also called Alice in Wonderland syndrome), hallucinations in which people or animals appear smaller than they would be in real life, are common in cases of peduncular hallucinosis. Most patients exhibit abnormal sleep patterns characterized by insomnia and daytime drowsiness. Peduncular hallucinosis has been described as a “release phenomenon” due to damage to the ascending reticular activating system, which is supported by the sleep disturbance characteristic of this syndrome. In most cases, people are aware that the hallucinations are not real. However, some people experience agitation and delusion and mistake their hallucinations for reality. Cause Peduncular hallucinosis is attributed to a range of various pathologies such as vascular and infectious midbrain, pontine and thalamic lesions, local subarachnoid hemorrhage, compression by tumors, basilar migraine, basilar vascular hypoplasia, and following regional surgical or angiographic interventions. These pathologies are mainly near the base of the brain and the hallucinations have gone away in patients that had their pathology corrected such as the removal of a tumor. The most commonly reported hallucinations are animals, people of any age, scary or deformed faces and heads, landscapes, or people walking in a line. Lesions The lesions that disturb brainstem reticular formation or thalamic targets