Complex visual hallucinations. Clinical and neurobiological insights

Area of Science:

• Neuroscience
• Neurology
• Sleep Medicine

Background:

• Complex visual hallucinations are reported in normal individuals during sleep transitions and in various pathological conditions.
• These hallucinations often feature stereotyped, vivid imagery, including animals and human figures in dramatic settings.
• Associated conditions include narcolepsy-cataplexy, Parkinson's disease, Lewy body dementia, migraine coma, Charles Bonnet syndrome, schizophrenia, and epilepsy.

Purpose of the Study:

• To describe cases of hallucinosis from diverse causes.
• To propose three underlying mechanisms for complex visual hallucinations.
• To explore the role of brainstem lesions and thalamocortical modulation.

Main Methods:

• Case descriptions of hallucinosis.
• Review and expansion of existing hypotheses on hallucination mechanisms.
• Discussion of neuroanatomical pathways and their disruption.

Main Results:

• Epileptic hallucinations may arise from direct cortical irritation.
• Visual pathway lesions can lead to defective processing or release phenomena.
• Brainstem lesions affecting cholinergic and serotonergic pathways, often linked to sleep disturbances, are implicated.

Conclusions:

• Complex visual hallucinations can result from direct cortical irritation, visual pathway lesions, or brainstem pathway dysfunction.
• Lesions outside the primary visual system may disrupt thalamocortical relationships, causing a release phenomenon.
• Perturbation of a distributed neural matrix may explain similar hallucinations from diverse insults.