3.1 Publication trend analysis
A total of 625 publications met the inclusion criteria, consisting of 455 articles and 170 reviews. According to Fig. 2, there was an overall upward trend in the number of annual publications from 2009 to 2023. The lowest number of publications was in 2009, with four publications, while the highest number of publications was in 2023, with 128 publications. There was a highlight that after the concept of GS was put forward in 2012, the number of publications has gradually increased, especially from 2017 to 2023, showing the increasing attention from researchers in recent years. However, reviews accounted for a significant proportion of publications (27.2%), and more innovative studies will be needed in the future.
Figure 2 Publication trend
3.2 Countries or regions analysis
Research on GS and cognitive function was conducted in 75 countries or regions from 2009 to 2023. The countries or regions' collaboration network was constructed using CiteSpace (Fig. 3A). Each node represented a country. Nodes with purple rings represented high centrality (centrality ≥ 0.1), indicating that they were influential and their publications were high cited within a short period [21]. The USA ranked first with 207 publications, and China and the United Kingdom followed with 191 and 108 publications, respectively. The top 10 countries or regions in the number of publications are displayed in Fig. 3B. The geographic distribution of publications produced by countries or regions is shown in Fig. 3C.
Figure 3A. Countries/regions network analysis
Figure 3B. Number of publications in the top 10 countries/regions
Figure 3C. Geographical distribution map of national/regional publications
3.3 Institutions analysis
Research on GS in cognition was conducted in 149 institutions from 2009 to 2023. The institution's collaboration network was constructed using CiteSpace (Fig. 4). The top 10 institutions with the highest number of publications are shown in Table 1. The majority of those with the most publications are organizations from the UK, followed by the USA. While China has a high volume of publications, there was no close cooperation between the organizations. Among these, Harvard University (37 publications), the University of Edinburgh (35 publications), and the University of London (34 publications) were the top three institutions in terms of the number of published studies.
Figure 4 Institutions collaboration network
Table 1 Top 10 institutions
3.4 Journals and co-cited journals analysis
VOSviewer was used to analyze cited journals (Fig. 5) and Citespace was used to analyze co-cited journals (Fig. 6). Between 2009 and 2023, research on GS and cognition was published in 253 academic journals. Among them, “Frontiers in aging neuroscience” ranked first with 41 publications followed by frontiers in neurology with 24 publications. A co-citation can reveal influential journals in a particular field by measuring the frequency with which two journals are cited together in the same publication [23]. Among co-cited journals, Neurology (507), Lancet Neurology (435), and Stroke (433) were the top three co-cited journals, indicating their high academic prestige in the field of GS in cognition.
Table 2. Top 10 journals and co-cited journals
Figure 5 Cited journal analysis
Figure 6 Co-cited journal analysis
3.5 Authors and co-cited authors analysis
Citespace was used to analyze the collaboration of authors (Fig. 7) and co-cited authors (Fig. 8). The count, centrality, and year of authors and co-cited authors are listed in Table 3. More collaborative communication between authors can be seen. The authors with the most publications were Wardlaw, Joanna M (25), followed by Charidimou, Andreas (16) and Nedergaard, Maiken (13). Wardlaw, Joanna M was also the most frequently co-cited author (306), showing the research strength and hot topics. Ilff JJ (210) and Pantoni L (146) also had high-quality of publications.
Figure 7 Authors collaboration network
Figure 8 Co-cited author's network
Table 3 Top 10 authors and co-cited authors
3.6 Most cited articles analysis
The top 10 cited articles are shown in Table 4. Nine out of ten were published in journals classified as Q1 and with IFs greater than 10. Three of the top ten cited articles were from Wardlaw JM and two were from Mestre H. The article entitled “The glymphatic pathway in neurological disorders” published in Lancet neurology had the most citations.
Table 4 Top 10 cited articles
3.7 Keyword co-occurrence, clustering analysis
Keywords not only reflect the focus in a particular research area but also the heat and direction of research in a specific field. Keywords were summarized from the data in the WosCC and imported into CiteSpace. In our research, a total of 135 keywords were extracted and the total cumulative frequency of keywords amounted to 3219. Top 20 keywords as shown in Table 5. Vosviwer was uesd to analysis keywords hotspots (Fig. 9). Up to now research has focused more on the link between the glymphatic system and cognitive impairment, including “alzheimers disease” and “dementia”, and “small vessel disease” and “mri” are also hotspots. These different research hotspots contribute to optimising and enhance the development of GS in cognition.
Table 5 Top 20 keywords
Figure 9 Keywords co-occurrence density map
VOSviewer was used to perform clustering network analysis on keywords (Fig. 10). The same meaning keywords were merged: (1) AQP4, AQP-4, aquaporin-4 and aquaporin 4; (2) alzheimers'-disease, alzheimers-disease, alzheimer-disease, and alzheimer disease; (3) blood-brain barrier, blood-brain-barrier, and blood brain barrier; (4) white-matter hyperintensities and white matter hyperintensities. A total of 52 keywords were extracted, by defining keyword occurrences bigger than or equal to 25 as the extraction threshold and combining keywords with the same meaning. There were three main clusters: The red area is cluster 1, which contained 20 keywords with core cluster terms such as Alzheimers-disease, amyloid-beta, aquaporin 4, and blood-brain barrier. The clustering themes were vascular impairment on Alzheimers-disease. The green area is cluster 2, containing 18 keywords with core cluster terms such as association, microbleeds, and dementia. The clustering themes were cerebral small vessel disease on cognitive impairment such as dementia. The blue area is cluster 3, containing 13 keywords with core cluster terms such as age, MRI and small vessel diseases. The clustering themes were the impact of risk factors such as age on small vessel diseases and MRI.
Figure 10 Keywords clustering network
3.8 Keywords timeline and emergence analysis
CiteSpace was used to present keywords timeline (Fig. 11) and emergence analyze (Fig. 12). Alzheimer's disease and perivascular spaces had been a hot topic for a long time and from 2017 research on GS increased. Some studies on mechanisms and MRI in central nervous system were also hotspots. Research on a beta preceded research on aquaporin 4 and clearance and this was also related to the time of GS concept. The keyword emergence analysis of the WoSCC publications on GS in cognition generated 19 emergent terms. “Virchow robin spaces”, “vascular dementia”, and “autosomal dominant arteriopathy” were the first, and “white matter lesions” were the strongest. The longest-lasting keyword was white matter lesions. Studies on small vessel disease emerged from 2011 to 2014, and cerebral small vessel disease-related decreases in cognition were found to be associated with enlarged virchow-robin spaces [24]. “System” and “mouse model” were words that have emerged in recent years.
Figure 11 Keywords timeline analysis
Figure 12 Keywords emergence analysis