Aug 2026· Neurophysiologie clinique· Vol 56 5, pp.
103192
· 0 citations· 43 references
Medicine
TL;DR
Overall, PD is characterized by multilevel visual-pathway dysfunction rather than a single cortex-specific biomarker, which means electrophysiological measures should be controlled before electrophysiological measures are used for localization, stratification, or prognosis.
Abstract
Parkinson's disease (PD) can disrupt retinal, early cortical, oscillatory, and distributed visuoperceptual processing. This structured integrative review synthesized human evidence from pattern electroretinography (PERG), electroretinography (ERG), optical coherence tomography (OCT)-linked and conventional visual evoked potentials (VEPs), visual event-related potentials (ERPs), electroencephalography (EEG), steady-state visual evoked potentials (ssVEPs), and occipital transcranial magnetic stimulation-electroencephalography (TMS-EEG), with searches verified up to 18 July 2026. Findings were organized into four domains: 1) Retinal and retinocortical contributions: retinal dysfunction can delay or attenuate afferent input, yet concurrent retinal physiology is rarely measured; therefore VEP abnormalities cannot generally be assigned specifically to cortex. 2) Early visual encoding: prolonged pattern-reversal P100 latency is the most reproducible finding, including a pooled 6.04-ms delay across 20 case-control studies, whereas amplitude findings are inconsistent. 3) Oscillatory dynamics: PD-specific ssVEP evidence suggests altered contextual gain, but it derives from one small unreplicated study; gamma-band and task-EEG findings remain sparse and confound-sensitive. 4) Higher-order and network-level processing: visual ERPs, resting microstates, and occipital TMS-EEG indicate possible associations with hallucinations, cognition, and network connectivity, but current studies are cross-sectional or unreplicated. Overall, PD is characterized by multilevel visual-pathway dysfunction rather than a single cortex-specific biomarker. Ophthalmic status, retinal physiology, medication state, cognition, mood, sleep, and recording quality should be controlled before electrophysiological measures are used for localization, stratification, or prognosis.
This narrative review synthesizes preclinical and early-phase clinical evidence for 40 Hz non-invasive brain stimulation across five delivery modalities and concludes that multisensory combined stimulation currently represents the approach with the most promising early translational signal.
Retinitis pigmentosa (RP) progressively deprives the retina of input, but whether the responsiveness of the visual cortex declines in parallel, remains preserved, or increases through compensatory gain remains unclear. Indeed, a weaker visually evoked response cannot, on its own, distinguish these possibilities, since it is equally compatible with a passively degraded input and with an actively recalibrated cortex. We combined spatially resolved steady-state visual evoked potentials (SSVEPs), which index stimulus-driven activity, with transcranial magnetic stimulation combined with electroencephalography (TMS-EEG), which probes cortical reactivity independently of vision, in patients with RP and in healthy controls. Nine patients (PTs) with RP (five women, age range 28 to 69 years) and nineteen sex-, age-, and handedness-matched healthy controls (thirteen women, mean age 42.6 years) were tested. They underwent SSVEP recordings to stimuli presented at three eccentricities (central, intermediate, peripheral) and single-pulse TMS-EEG over the left and right occipital cortex and, as a non-visual control site, the dominant motor cortex. We quantified SSVEP amplitude and phase at 12 Hz, early TMS-evoked potentials, oscillatory power, inter-trial phase synchrony, and functional connectivity and graph-theoretical network measures derived from the weighted phase lag index. SSVEP amplitude followed the expected central-to-peripheral gradient: PTs were comparable to healthy controls at the center, reduced but still above their own resting baseline at intermediate eccentricity, and no longer distinguishable from baseline in the periphery; phase differed from controls in a quarter of the central and half of the intermediate sectors. Occipital stimulation elicited a larger early negative deflection after left-hemisphere stimulation in PTs compared to controls, a stronger beta-band event-related spectral perturbation after stimulation of either hemisphere, and stronger, more efficiently distributed post-stimulus connectivity, despite comparable pre-stimulus connectivity, resting motor threshold, and most early evoked components. The pattern was site- and hemisphere-specific: left occipital stimulation produced widespread, mainly contralateral effects; right occipital stimulation a more circumscribed ipsilateral one, and motor cortex stimulation showed altered alpha-band activity without the bilateral occipital beta effect. Together, these results show that progressive retinal deafferentation in RP does not produce a parallel decline in cortical responsiveness. Visually driven activity weakens with eccentricity, while direct cortical perturbation reveals preserved and, at selected sites, enhanced reactivity. This dissociation is consistent with a homeostatic increase in cortical gain rather than a uniform loss of cortical function, and indicates that the deafferented cortex retains, and in places strengthens, its capacity to respond as retinal input deteriorates.
Ilaria Siviero, A. Verroca, S. Mele et al.· bioRxiv· 0 citations
Alzheimer’s disease (AD) extends beyond the brain to the visual system, offering a promising window for pathology, monitoring, and intervention. This review synthesizes evidence on AD-related visual impairments across molecular, cellular, circuit, and cortical levels. We examine the eye–brain pathological relationship as a working framework, noting experimental evidence for brain-to-eye amyloid-β (Aβ) transport in mouse models and associations between retinal and cerebral pathology in humans, while emphasizing that bidirectional pathological transport has not been established. Structural and functional changes in the retina, optic nerve, and visual cortex are reviewed, alongside white matter damage and posterior cortical atrophy patterns. We evaluate emerging multimodal tools (OCTA, ERG, and hyperspectral imaging) that shift diagnosis toward an integrated “structure–vessel–function” assessment. We critically examine non-pharmacological interventions, including 40 Hz gamma stimulation and photobiomodulation, discussing their mechanisms, translational challenges, and the dissociation between structural and cognitive outcomes. We propose the visual system as a candidate pathological window, a quantitative monitoring platform, and an investigational intervention entry point in Alzheimer’s disease. However, clinical translation of these applications requires standardized acquisition protocols, prospective longitudinal validation, and robust mechanistic evidence. To advance this agenda, we identify three priorities: multimodal data integration, closed-loop neuromodulation strategies, and methodologically rigorous validation frameworks.
Yi-Man Liu, Jun-Yi Lu, Zile Zhang et al.· Vision· 0 citations
A scoping, narrative roadmap of SSVEP applications organized into three primary domains is provided, highlighting the versatility of SSVEPs in investigating neural mechanisms, supporting diagnosis and treatment of neurological and psychiatric conditions, and advancing brain-computer interface technology.
T. Tsoneva, P. Desain, G. G. Molina et al.· NeuroImage· 0 citations
Psychiatric symptoms in Parkinson's disease (PD) are highly prevalent and challenging to treat. This study maps oscillatory neural activity to diverse psychiatric symptoms in PD, using resting-state subthalamic nucleus (STN) local field potentials (LFPs) and frontal EEG in 55 PD patients undergoing deep brain stimulation (DBS). We tested whether 1) distinct psychiatric symptoms are associated with frequency-specific neural signatures using power spectral analyses and machine learning, across both eyes-open and eyes-closed sensory-attentional states. 2) symptom encoding is spatially segregated within the STN, with electrophysiological (defined by peak spectral power) and anatomical (defined by STN boundaries) mappings providing complementary information. 3) these regions exhibit distinct structural connectivity profiles, assessed using STN-seeded tractography from the UK Biobank normative connectome. Our analysis revealed spectral, spatial, and connectivity segregation. Depression was associated with increased alpha power, primarily detected by anatomical mapping, whereas apathy (increased high beta) and trait impulsivity (reduced low gamma) were detected with both anatomical and electrophysiological STN mapping. UK Biobank analyses further showed that STN-based alpha clusters (depression-related) preferentially connected with prefrontal, orbitofrontal, and cingulate cortices, while peak low-beta clusters (motor-related) connected with SMA and premotor areas. High-beta and low-gamma bands showed convergent connectivity across peak and STN-based clusters despite ventral-dorsal differences. These findings disentangle neurophysiological substrates of PD psychiatry, identifying symptom-specific biomarkers and informing targeted neuromodulation strategies.
Linbin Wang, Ying Zhao, Peng Huang et al.· Brain : a journal of neurolo...· 0 citations
Early identification of mild cognitive impairment in Parkinson’s disease (PD-MCI) is crucial for delaying dementia progression, yet the mechanisms underlying cortical excitability and time-varying network dysconnectivity remain elusive. This study utilized transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) to characterize time-varying directed brain network alterations targeting the right posterior parietal cortex (PPC) in PD-MCI. 20 PD patients were categorized into PD-MCI and cognitively normal (PD-NC) groups using the Montreal Cognitive Assessment (MoCA). Adaptive directed transfer function (ADTF) was applied to assess whole-brain directed time-varying functional connectivity following right PPC stimulation. Machine learning models were then employed to classify PD-MCI using spatiotemporal network features. Compared to PD-NC, the PD-MCI group exhibited significantly reduced cross-regional directed connectivity across the full 1–45 Hz frequency band. Notably, this decoupling was most pronounced in the γ band, with widespread disruptions across multiple time windows. Abnormal connectivity strengths were significantly positively correlated with MoCA cognitive scores. A KNN classification model was constructed based on 5 key spatiotemporal features, and using 5 repetitions of 5-fold cross-validation, ultimately achieving an optimal classification accuracy of 93.33%. These findings reveal that PPC-targeted, full-frequency time-varying network decoupling is a core neuropathological mechanism in PD-MCI. The identified spatiotemporal features hold promise as objective biomarkers for the early identification of PD-MCI, providing a foundation for early diagnosis and targeted neuromodulation.
Qi Zhu, Guangying Pei, Mengxuan Hu et al.· Journal of Physics, Conferen...· 0 citations
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