Summary:
A clinical neurophysiology study reveals that sleep-like slow brain waves frequently intrude into conscious wakefulness in patients with Parkinson’s disease, correlating directly with minor hallucinations and impaired cognitive functioning. Conducted by Fosco Bernasconi and colleagues, the high-density electroencephalography (EEG) investigation evaluated 84 individuals with Parkinson’s disease alongside 30 healthy older adults.
The researchers discovered that patients not only exhibited higher frequencies of wakeful slow waves per minute but also that heightened wave amplitude tracked closely with psychotic symptoms and worse neuropsychological scores, suggesting wake slow-wave dynamics could serve as non-invasive prodromal biomarkers.
Key Facts:
- Intrusion of Sleep Waves During Wakefulness: Patients with Parkinson’s disease displayed a significantly greater number of sleep-like slow waves per minute while awake compared to healthy age-matched control participants.
- Biomarker for Hallucinations and Cognitive Decline: Patients experiencing minor hallucinations exhibited slow waves of greater amplitude; these enlarged slow-wave patterns also strongly correlated with poorer cognitive performance on standardized clinical assessments.
- Prodromal Risk Stratification: The investigators suggest that atypical awake slow-wave activity may emerge during the earliest prodromal stages of Parkinson’s disease, offering a potential electrophysiological tool to identify individuals at elevated risk before classical motor or severe cognitive signs manifest.
Source: AAAS
Parkinson’s disease is traditionally diagnosed and monitored through cardinal motor signs: resting tremor, muscle rigidity, bradykinesia, and postural instability. However, patients and caregivers frequently report that non-motor complications, particularly cognitive decline, sleep architecture disruptions, excessive daytime sleepiness (EDS), and perceptual distortions, impose the greatest burden on daily quality of life.
In healthy brains, low-frequency slow waves (< 4 Hz), typically encompassing delta rhythms and slow oscillations) serve as the electrophysiological hallmark of non-rapid eye movement (NREM) slow-wave sleep. While healthy individuals may occasionally show transient local slow waves during brief episodes of mind-wandering or acute fatigue, wakefulness is predominantly governed by desynchronized, higher-frequency oscillations.
While previous sleep laboratory research established that nocturnal slow waves are degraded and fragmented in neurodegenerative disorders, whether these sleep-like slow oscillations abnormally penetrate the conscious, awake brain in Parkinson’s disease has remained an unresolved question.
To address this, a research team led by Dr. Fosco Bernasconi utilized electroencephalography (EEG) to examine awake cortical dynamics in 84 individuals diagnosed with Parkinson’s disease and 30 healthy elderly control participants.
Their findings demonstrate that sleep-like slow waves systematically breach wakefulness in Parkinson’s patients, directly correlating with cognitive deficits and the presence of minor hallucinations.
Local Sleep in the Conscious Brain
The investigators recorded resting-state EEG data while participants remained awake in a controlled testing environment, simultaneously evaluating subjective and objective daytime sleepiness.
The electrophysiological analysis revealed that patients with Parkinson’s disease experienced both heightened daytime sleepiness and a significantly higher incidence of sleep-like slow waves per minute across the scalp compared to the healthy control group.
This phenomenon aligns with the emerging neuroscience concept of “local sleep”, a state wherein isolated cortical regions enter a transient, sleep-like bistable state of neuronal silence while the rest of the cerebrum remains awake. In Parkinson’s disease, the degeneration of ascending subcortical wake-promoting monoaminergic and cholinergic pathways (originating in the locus coeruleus, raphe nuclei, and basal forebrain) may undermine the thalamocortical mechanisms responsible for sustaining wakeful oscillatory tone.
The Link to Hallucinations and Cognitive Deterioration
Beyond the baseline frequency of slow waves, the structural geometry of the waveforms yielded striking clinical insights:
- Hallucination Severity: In patients who reported minor hallucinations, such as presence hallucinations (feeling someone is nearby) or passage hallucinations (fleeting visual movements in the periphery), the amplitude of awake slow waves was significantly elevated compared to non-hallucinating patients.
- Cognitive Correlation: Higher slow-wave amplitudes also correlated with poorer scores across standardized clinical neuropsychological assessments of executive function and memory.
These findings suggest that when cortical networks fall into slow-wave synchronization during the day, the brain’s ability to correctly parse sensory feedback and maintain veridical perceptual boundaries is compromised. The intrusion of sleep-like oscillations into waking perceptual networks may provide the electrophysiological foundation from which illusions and hallucinations emerge.
“Future studies should investigate whether [sleep-like slow wave] alterations are already present at a prodromal stage of [Parkinson’s disease],” write Bernasconi and colleagues, noting that quantitative slow-wave profiling could aid in identifying populations at elevated risk.
Clinical Potential as a Prodromal Biomarker
Because non-motor indicators such as REM sleep behavior disorder (RBD), mild cognitive changes, and visual phenomena can predate motor onset by up to a decade, identifying objective, scalable biomarkers is a clinical priority.
High-density EEG is non-invasive, accessible, and significantly less resource-intensive than molecular positron emission tomography (PET) or cerebrospinal fluid sampling. If atypical awake slow-wave oscillations can be verified in prodromal cohorts, clinicians could deploy rapid daytime EEG protocols to stratify individuals at high risk for Lewy body pathology, opening a window for early neuroprotective interventions before extensive dopaminergic denervation occurs.
Questions and Answers
What are slow brain waves, and when do they normally occur?
Slow brain waves are low-frequency electrical oscillations (such as delta and sub-delta waves) that typically appear during deep, restorative non-REM sleep. In healthy individuals, they indicate reduced cortical excitability, although brief, localized bursts can occasionally emerge during daytime fatigue or mind-wandering.
How do wakeful slow waves differ in Parkinson’s disease patients?
Patients with Parkinson’s disease experience a significantly higher rate of sleep-like slow waves per minute while awake compared to healthy older adults. Furthermore, those who experience minor hallucinations exhibit slow waves with markedly larger amplitudes.
Why does this study matter for the early diagnosis of Parkinson’s?
Because daytime slow-wave abnormalities directly track with hallucinations and cognitive decline, researchers believe these wave patterns could emerge during the prodromal (pre-motor) phase of the disease. Measuring awake slow waves via non-invasive EEG could provide an objective biomarker to detect Parkinson’s risk years before irreversible neurodegeneration sets in.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this Parkinson’s disease Research:
- Media Contact: AAAS Media
- Source: AAAS
- Image Credit: Image credited to Neuroscience News
- Original Research is Open Access: Science Translational Medicine (Nov 11, 2026). “Sleep-like slow waves during wakefulness are associated with hallucinations and poorer cognition in Parkinson’s disease.” Authors: Fosco Bernasconi, Thomas Andrillon, Juan Carlos Farah, Isabelle Arnulf, Sophie Schwartz, Jevita Potheegadoo, Saul Martínez-Horta, Javier Pagonabarraga, Jaime Kulisevsky, and Olaf Blanke.
- DOI: 10.1126/scitranslmed.aec1215
Abstract
Sleep-like slow waves during wakefulness are associated with hallucinations and poorer cognition in Parkinson’s disease
Slow waves during sleep are fundamental for neural homeostasis, metabolic regulation, and waste clearance and are known to be altered in neurodegenerative diseases. Sleep-like slow waves (SLSWs) have been observed in awake, healthy individuals, where they are linked to fluctuations in vigilance and mind-wandering.
Whether SLSWs are altered in Parkinson’s disease (PD), and whether such alterations contribute to psychiatric or cognitive complications, remains unknown.
In a cohort of 84 nondemented patients with PD and 30 healthy older adults, we found that SLSWs occurred more frequently in patients with PD. Hallucinatory traits in patients with PD were associated with higher SLSW amplitude, especially over frontocentral regions. Moreover, more prominent SLSWs were associated with poorer cognitive functions.
We conclude that, whereas slow waves during sleep have positive physiological functions, exacerbated diurnal SLSWs may reflect responses related to PD neuropathology, at the cost of hallucinations and reduced cognitive function.
