Hallucinogenic mechanisms: pathological and pharmacological insights

Understanding the neurological mechanisms responsible for misperceptions and hallucinations remains a significant challenge in clinical neuroscience. Disorders of perception can occur in each sensory domain and in addition, the disorder can be provoked by a wide array of differing pathophysiological processes ranging from cell death to the ingestion of a range of pharmaceutical agents. This complexity has made it difficult to draw conclusions as to whether there exists a 'common neural pathway' that underlies all hallucinations. Such a mechanistic explanation of hallucinations would need to encompass a large clinical spectrum of disorders including neurotransmitter disturbances and impairment within the neural centres of sensory perception, as well as the mechanisms controlling attention and conscious awareness. This chapter provides an overview of the range of these disorders whilst offering possible mechanisms and sites for pathology in each case.