Hallucinations Involving Cranial Nerve FunctionT

Abstract

Hallucinations are sensual perceptions without an external stimulus and can occur in all modalities of the senses, i.e., auditory, visual, olfactory, gustatory, and tactile. The reasons for their occurrence are manifold; however, they are generally associated with mental health issues and psychiatric diseases. It is important to be aware that auditory sensations like hearing voices do also occur in the general healthy population and it is crucial to differentiate between a harmless alteration and some serious organic or psychiatric disease. The prevalence of auditory hallucinations ranges, depending on the source, from 5% to 28% in the general population to up to 75% in patients with schizophrenia. The most common hallucinations are auditory, followed by visual, tactile or haptic, olfactory, gustatory, and cenesthetic or visceral.

Neurologists might be interested especially in sensations within the areas of the sensory cranial nerves, i.e., the olfactory nerve (I), optic nerve (II), auditory nerve (VIII), and glossopharyngeal nerve (IX). Visual hallucinations most often come together with a severe malfunctioning or damage of cerebral functions, either because of systemic diseases or direct cerebral lesions. Olfactory and gustatory sensations are often associated with severe psychiatric conditions like a major depressive episode.

This article provides an overview of hallucinations involving cranial nerve function. Furthermore, hands-on advice on how to recognize and diagnose hallucinations in psychiatric diseases are given, and their specific traits are illustrated.

Author of this chapter: Simon Grisold.