[A review of the pathogenesis of the hallucinatory state. A description of four case]

A hallucination is a sensorial experience occurring in the absence of external stimuli. It may show as psychological or organic disorders. The main causes are lesions of the central nervous system and of the sensorial organs. The hallucination may present with or without critical perception but always appears to be a real experience.

We describe four patients diagnosed as having hallucinations secondary to known lesions. The first two had visual hallucinations and cerebral ischaemia, the first in the dorso-lateral region of the medulla oblongata and the second in the left parietal lobe. The other two had peripheral sensorial defects. The third patient had simultaneously an ophthalmic disorder and visual hallucinations, and the fourth had chronic hypoacusia and auditory hallucinations. All showed structured sensorial hallucinations with critical appraisal of these hallucinations.

In this paper we review the pathogenesis of the organic hallucinatory state. The main mechanisms are proposed: by means of liberation (destruction of inhibitory structures) and by means of irritation (anomolous excitation of cerebral structures). Also we point out the difference between a hallucination and psychiatric disorders, mainly in three aspects: presence of the known organic lesion, critical appraisal of the perception in spite of it appearing as real to the patient, and the absence of associated psychiatric pathology.