Chapter 17: Hallucinations & Related Neuropsychological Conditions

Hallucinations & Related Neuropsychological Conditions begins by establishing clear clinical definitions, distinguishing hallucinations (perceptual experiences in the absence of external stimuli) from illusions (distortions of existing stimuli) and delusions (fixed false beliefs regarding reality). The text categorizes these experiences based on their complexity—ranging from unformed photopsias to formed complex imagery—and their sensory modalities, including visual, auditory, tactile, olfactory, gustatory, and visceral. A major focus is placed on visual hallucinations, exploring their manifestation in conditions such as Charles Bonnet syndrome (hallucinations following visual loss), peduncular hallucinosis resulting from brainstem lesions, and release hallucinations associated with visual field defects. The authors also detail how neurodegenerative disorders like Parkinson’s disease, Alzheimer’s disease, and Dementia with Lewy Bodies present unique hallucinatory profiles, often linked to cognitive decline and specific neurochemical imbalances. Beyond visual symptoms, the chapter explores nonvisual modalities, such as auditory commands in schizophrenia, phantom limb sensations in amputees, and olfactory or gustatory auras associated with temporal lobe epilepsy. Furthermore, it addresses complex misidentification syndromes, including Capgras syndrome, where patients believe familiars are imposters, and the phantom boarder sign, the belief that uninvited guests reside in one's home. The discussion on pathogenic mechanisms highlights theories of perceptual release, CNS hyperexcitement, and the disruption of dopaminergic, cholinergic, and serotonergic systems. Finally, the chapter outlines treatment paradigms, emphasizing the management of underlying causes and the judicious use of antipsychotics, cholinesterase inhibitors, and anticonvulsants to alleviate distressing symptoms.