Approximately 30 % of the total volume of the thalamus consists of the pulvinar nucleus, the largest nucleus in the thalamus. The pulvinar is cytoarchitectonically classified into anterior pulvinar (PuA), inferior pulvinar (PuI), medial pulvinar (PuM), and lateral pulvinar (PuL) sub-regions (Hakamata et al., 2016; Olszewski, 1952).

The pulvinar is a higher order nucleus that receives the majority of its inputs from the cortex and that sends outputs to it (Karunakaran et al., 2020). The broad and reciprocal connectivity between the pulvinar and cortical regions such as the frontal, parietal, temporal, occipital, and cingulate cortex suggests that the pulvinar contributes to advanced cognitive, affective, and somatosensory skills (Arend, Henik, and Okon-Singer, 2015; Guedj and Vuilleumier, 2020; Karunakaran et al., 2020; Koizumi et al., 2019; Romanski, Giguere, Bates, and Goldman-Rakic, 1997). The PuA, a sub-region of the human pulvinar mostly involved in somatosensory processing, is one of its most poorly understood components(Benarroch, 2015). The PuM is the largest of the pulvinar sub-regions. In the light of its reciprocal connectivity with the posterior parietal, inferior temporal, cingulate, restrosplenial, and prefrontal cortical areas, it has been linked to directed attention, executive functions, and working memory, as well as visuomotor, auditory, somatosensory, and other elements of higher cognitive processing (Homman-Ludiye and Bourne, 2019). Similarly, due to their extensive connections with visual cortical regions extending from the occipital lobe to the temporal and parietal lobes, the PuI and PuL are frequently referred to as the ‘visual pulvinar’ (Bridge, Leopold, and Bourne, 2016). For example, Kaas and Lyon (Kaas and Lyon, 2007) presented evidence that the PuI may act as a subcortical component of the dorsal stream, while the PuL is dedicated to the ventral stream of cortical processing, suggesting a critical role for the pulvinar in modulating visual attention processing (Fischer and Whitney, 2012; Hwang, Bertolero, Liu, and D’Esposito, 2017).

Several motor and non-motor deficits have been reported in pulvinar dysfunctions and lesions. From that perspective, pulvinar lesions can result in attentional deficits, neglect syndromes, and motor movement abnormalities, as well as fear recognition difficulty (Arend, Rafal, and Ward, 2008; Benarroch, 2015; Bruzzone, Gill, and Ruland, 2016; Kim, Kyeong, Ahn, and Park, 2017; Ward, Calder, Parker, and Arend, 2007; Wilke et al., 2018; Wilke, Turchi, Smith, Mishkin, and Leopold, 2010). Guedj and Vuilleumier performed data-driven analysis combined with meta-analysis to decode the role of the pulvinar in cognition by parcellating it into its various sub-regions (clusters). The results revealed that each sub-region possesses distinct and extensive functional connectivity with various brain areas, providing novel evidence of the pulvinar’s role in cognition by coordinating information throughout the brain network.(Guedj and Vuilleumier, 2020) It is therefore not surprising that pulvinar pathology should be involved in a range of neuropsychiatric and neurodegenerative disorders (Ayyildiz, Rodriguez-Manrique, Ayyildiz, Colak, and Koch, 2025; Beheshti, Perron, and Ko, 2024; Yulug et al., 2024). Numerous investigations have shown that the pulvinar plays a crucial role in both Lewy Body dementia and Alzheimer's disease (Erskine et al., 2017; B. D. Power and Looi, 2015; Velioglu et al., 2022). Similarly, grey matter volume differences in the pulvinar were reported by Chen et al. in patients with Parkinson’s disease (PD) (Chen et al., 2020). Comparable pulvinar abnormalities have also been linked to the cognitive impairments seen in PD. In that context, several research groups have described altered pulvinar structure as a core component of the pathophysiology of cognitive dysfunctions, hallucinations and dementia in PD and LBD, making the pulvinar a well-established structure of interest in this field (Devenyi and Hamedani, 2024; Erskine et al., 2018). For instance, Matsuura et al.(Matsuura et al., 2019) reported that hypointensity in the pulvinar was associated with cognitive decline and hallucinations in patients with PD after deep brain stimulation surgery. This is suggested by the fact that attention deficits, motor symptoms and executive dysfunctions characterized by planning, and decision-making can be damaged in patients with PD (Dirnberger and Jahanshahi, 2013; Moustafa et al., 2016). A recent PD model has also implicated thalamic circuits in the progression of the disease, making these a novel and modifiable target for a circuit-based therapeutic approach. This also indicates that identifying the neural network mechanisms associated with motor and non-motor symptoms of PD might pave the way for the development of innovative circuit-based therapeutics (Zhang et al., 2022), also suggesting that the pulvinar may be involved in PD. Despite these promising findings, there remains limited evidence on the neuroimaging correlates of cognitive differences identified through practical cognitive screening tools, such as the mini-mental state examination (MMSE), in distinguishing early Parkinsonism from healthy aging. In light of this evidence, the primary objective of our functional connectivity analysis was to determine the role of the pulvinar sub-regions and their connections in cognitive impairment and motor impairment in PD.

The purpose of this study was therefore to investigate the resting state functional connectivity and perform grey matter volume analysis of the PuA, PuI, PuL, and PuM in elderly individuals and patients with PD dementia by using a practical cognitive tool like Mini-Mental State Examination (MMSE). In light of the absence of a practical clinical approach and the lack of a well-established association between the pulvinar’s subregions and neurodegenerative disorders, we sought to investigate potential alterations in functional connectivity and grey matter volume within the PuA, PuI, PuM, and PuL subregions in individuals with PD. Given the aforementioned gaps and inconsistencies in existing knowledge, we pose this as an open research question, investigating whether such alterations may be observed. This approach aligns with the uncertainty surrounding the relationship between the pulvinar’s subregions and PD, allowing for a more exploratory and nuanced investigation. Although macrostructural analysis of the pulvinar and its subregions is well-established, to date, no study has investigated the functional connectivity along with grey matter volume of the pulvinar subnuclei in patients with PD dementia. Given that the pulvinar is not a homogeneous anatomical structure and each subregion serves distinct functions, we believe that analyzing the functional connectivity of its subnuclei provides a more precise and meaningful interpretation.