Parkinson’s disease is widely recognized for its tremor, slowed movement and muscle rigidity, but a new study is drawing attention to another dimension of the disorder: the brain chemistry that may connect hallucinations with the loss of cognitive and sensory stability. In a paper published in npj Parkinson’s Disease, Mehta, O’Donnell, Eid and colleagues examine the relationship between cholinergic deficits and hallucinations in Parkinson disease, focusing on how disruption of acetylcholine signaling may help explain one of the condition’s most unsettling non-motor symptoms.
Hallucinations in Parkinson’s disease are not rare curiosities confined to advanced cases. Many patients experience vivid visual images, fleeting figures or fully formed scenes that appear real despite having no external source. For some, these experiences are mild and easily dismissed. For others, they can become persistent, frightening and deeply disruptive, affecting sleep, independence, medication decisions and relationships with caregivers. The new research places the cholinergic system—the network of neurons and chemical signals built around acetylcholine—at the center of this clinical mystery.
Acetylcholine is a neurotransmitter essential for attention, learning, memory and the brain’s ability to interpret incoming sensory information. In healthy brain circuits, cholinergic activity helps regulate which signals receive priority and which are suppressed as irrelevant. This filtering function is especially important for maintaining a stable perception of reality. When cholinergic pathways deteriorate, the brain may become less capable of distinguishing internally generated images, memories or expectations from information arriving through the eyes and ears.
Parkinson’s disease is primarily associated with the loss of dopamine-producing neurons in a region called the substantia nigra. That dopamine deficit produces the movement symptoms that define the disease and forms the basis for treatments such as levodopa. Yet Parkinson’s is not a single-neurotransmitter disorder. As the disease progresses, damage may extend into cholinergic regions, including neurons originating in the basal forebrain and brainstem. These systems influence cortical arousal and attention, making their decline a possible biological bridge between Parkinson’s disease, cognitive impairment and hallucinations.
The study’s title reflects a research question with important consequences for diagnosis and treatment: are hallucinations simply a side effect of Parkinson’s medications, or do they also signal an underlying failure of the brain’s cholinergic machinery? Dopaminergic drugs can intensify hallucinations in some patients by altering activity in circuits involved in perception and reward. However, medication exposure alone does not explain every case. Hallucinations may occur in people receiving different treatment regimens, and vulnerability appears to vary according to age, cognitive status, sleep disruption and the wider pattern of neurodegeneration.
A cholinergic explanation does not replace these factors; it may help connect them. Reduced acetylcholine signaling can weaken attention, impair visual processing and limit the brain’s ability to correct perceptual errors. At the same time, Parkinson’s disease can affect networks responsible for dreaming and sleep-wake regulation. When these vulnerabilities overlap, internally generated imagery may intrude into waking consciousness. The result can be a perceptual experience that feels exceptionally convincing, even though the sensory evidence supporting it is absent.
This line of research also helps explain why cholinesterase inhibitors are sometimes considered in Parkinson’s disease dementia and related cognitive syndromes. These medications slow the breakdown of acetylcholine in the brain, potentially strengthening residual cholinergic signaling. Their clinical use is not a universal solution, and treatment decisions must account for side effects, disease stage and individual risk. Nevertheless, the cholinergic hypothesis offers a biological rationale for investigating whether restoring or supporting acetylcholine activity can improve attention and reduce hallucination-related distress in selected patients.
The implications extend beyond hallucinations themselves. A patient who sees people in an empty room may be experiencing a warning sign of broader network dysfunction rather than an isolated psychiatric symptom. Recognizing that possibility could encourage clinicians to assess cognition, vision, sleep, medication effects and autonomic symptoms more systematically. It may also reduce the stigma surrounding hallucinations by framing them as manifestations of neurodegenerative biology. For families, that shift can transform a frightening experience into a clinical signal that deserves careful evaluation.
The work by Mehta, O’Donnell, Eid and colleagues arrives as researchers increasingly view Parkinson’s disease as a disorder of interconnected brain systems rather than a condition defined only by movement. Mapping the relationship between cholinergic loss and hallucinations could eventually support more precise forms of care, including biomarkers that identify patients at risk before symptoms become severe. Future studies will need to clarify how cholinergic damage interacts with dopamine therapy, Lewy body pathology, visual impairment, sleep abnormalities and cognitive decline. For now, the research highlights a powerful idea: when perception begins to blur in Parkinson’s disease, the missing ingredient may be not only dopamine, but also the brain’s chemical capacity to keep reality in focus.
Subject of Research: Cholinergic deficits and hallucinations in Parkinson disease
Article Title: Cholinergic deficits and hallucinations in Parkinson disease
Article References: Mehta, J.S., O’Donnell, J., Eid, A.M. et al. “Cholinergic deficits and hallucinations in Parkinson disease.” npj Parkinson’s Disease (2026). https://doi.org/10.1038/s41531-026-01525-2
Image Credits: AI Generated
DOI: 10.1038/s41531-026-01525-2
Keywords: Parkinson’s disease, hallucinations, cholinergic deficits, acetylcholine, neurodegeneration, cognitive impairment, dopamine, brain chemistry, visual perception, neuroscience
Tags: acetylcholine signalingbrain chemistry in Parkinson’scholinergic deficitscholinergic system disruptioncognitive and sensory deficitshallucinations in Parkinson’simpact of neurotransmitter lossneurochemical basis of hallucinationsneurodegeneration and hallucinationsnon-motor symptoms of Parkinson’sParkinson’s diseasevisual hallucinations
