|Year : 2020 | Volume
| Issue : 3 | Page : 155-165
Global research output of the cerebellum: Yesterday, today, and tomorrow
Murat Golpinar1, Emre Demir2
1 Department of Anatomy, Faculty of Medicine, Hitit University, Çorum, Turkey
2 Department of Biostatistics, Faculty of Medicine, Hitit University, Çorum, Turkey
|Date of Submission||19-Jun-2020|
|Date of Acceptance||13-Aug-2020|
|Date of Web Publication||30-Sep-2020|
Dr. Murat Golpinar
Department of Anatomy, Faculty of Medicine, Hitit University, Çorum
Source of Support: None, Conflict of Interest: None
Introduction: The cerebellum has been regarded as a valuable research topic over the years because of its numerous roles in motor and nonmotor functions. The aim of the current study was to provide a comprehensive and holistic evaluation of publications concerning the cerebellum over the last 40 years which can be a potential guide for future research related to the cerebellum. Material and Methods: The Web of Science database was used to identify the publications relating to the cerebellum between 1980 and 2019. The identified publications were analyzed using the bibliometric approaches. The number of the publications concerning the cerebellum to be published between 2020 and 2028 was predicted using the linear regression analysis. Results: The literature review revealed a total of 33,186 publications. The top three active countries were found to be the USA (7362), Japan (2987), and the UK (1994). A positive and significant correlation was found between the number of cerebellum articles produced by the countries and the development indexes of the countries (r = 0.743, P < 0.001; r = 0.676, P < 0.001, r = 0.656, P < 0.001). The top three productive journals were found to be the Journal of Neuroscience, Brain Research, and Cerebellum. The total number of cerebellum publications is expected to continue in an increasing trend and reach a total of 891 publications at the end of 2028. Discussion and Conclusion: Recent studies on the cerebellum have mostly focused on the cerebellar degeneration, functional connections of the cerebellum, and its relationship with various diseases such as ataxia, schizophrenia, Parkinson's disease, autism, and aneurysms.
Keywords: Bibliometric analysis, cerebellum, neuroanatomy, scientometric analysis, trends
|How to cite this article:|
Golpinar M, Demir E. Global research output of the cerebellum: Yesterday, today, and tomorrow. J Anat Soc India 2020;69:155-65
| Introduction|| |
The cerebellum, which contains more than 50% of the neurons in the human brain, is a crucial component in the central nervous system. For many years, the cerebellum has been considered as primarily responsible for the coordination of movement and the maintenance of posture and balance. However, recent studies have indicated its contribution to a huge variety of cognitive, emotional, and behavioral functions.,, Due to its extensive reciprocal connectivity with sensorimotor and association areas of the cerebral cortex, thalamus, and spinal cord, the cerebellum performs various vital functions in humans. Studies have also shown that structural and functional cerebellar abnormalities are closely related to a wide range of neurodegenerative and psychiatric disorders, including Alzheimer's disease, Schizophrenia, Parkinson's disease, and Multiple sclerosis.,,, Due to its vital and different roles in motor and nonmotor functions, the cerebellum has been regarded as a valuable research topic over the past years.
Bibliometrics, based on the application of mathematical and statistical methods, is a commonly used approach for the descriptive analysis of the quality of scientific outputs such as books, articles, and reviews., It provides an objective and effective way for a detailed evaluation of the history, current state and future of scientific publications in a particular field or specific topic, both qualitatively and quantitatively. In bibliometrics, specific features of the scientific documents and publications are analyzed to determine the level of scientific communication. Bibliometric analysis also allows the comparisons to reveal the efficiency of the researchers, institutions, organizations, and countries in various research areas. In this way, bibliometric information enables the identification of global research patterns, dynamics, and trends in a scientific field or topic during a certain period. Therefore, the bibliometric approach reveals valuable and useful information for the comprehensive evaluation of the scientific outputs for both researchers and organizations., There have been many scientific papers concerning the cerebellum over the years, and studies on the cerebellum are still growing rapidly. However, there has been no detailed analysis performed on the scientific output in respect of the cerebellum to date. The aim of the present research was to perform a comprehensive and holistic analysis of the publications concerning the cerebellum published during the period from 1980 to 2019 through bibliometric approaches and to determine the evolving research trends on the cerebellum topic over the 40 years.
| Material and Methods|| |
Articles about the cerebellum were accessed through the Web of Science (WoS) database, using the keywords of “cerebellum, cerebellar, cerebelli, and cerebello” in the titles section of the articles (Search codes for repeatability were Title: [cerebellum] or Title: [cerebellar] or Title: [cerebelli] or Title: [cerebello] Refined by: Document Types: [Article] Timespan: 1980–2019. Indexes: SCI-Expanded, SSCI, A and HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI). All the articles on the cerebellum in WoS downloaded through this search method (accession date: January 15, 2019; the number of publications may vary according to the date of search) were analyzed bibliometrically. A web site (http://lert.co.nz/map/) was used to generate the world map. VOSviewer (Version 1.6.13, Leiden University: Centre for Science and Technology) package program was utilized for bibliometric web visualizations.
Statistical data analyses were performed using the SPSS software version 22.0 (SPSS Inc., Chicago, IL, USA, license: Hitit University). The normality of the data distribution was tested using the Kolmogorov–Smirnov test. According to the data distribution, the correlation analysis between the number of articles about the cerebellum and the Gross Domestic Products (GDP), GDP (at purchasing power parity) per capita (GDP PPP), and Human Development Index (HDI) were analyzed using the Spearman correlation test. The number of publications to be published in the following years was predicted using the linear regression analysis. Statistical significance was taken as P < 0.05.
| Results|| |
The literature review revealed in a total number of 33,186 publications. Of these publications, 22,084 (66.5%) were articles, 6070 (18.291%) were meeting abstracts, 1271 (3.830%) were reviews, 1221 (3.679%) were proceedings papers, 1070 (3.224%) were letters, and the rest were editorial materials (963), notes (824), corrections (181), book chapters (163), early access (38), correction additions (17), discussions (15), news items (13), book reviews (12), reprints (12), books (5), bibliography (1), biographical item (1), hardware review (1), item about an individual (1), and retraction (1). This study performed the bibliometric analysis of only 22084 publications that were in the article category. Of these articles, 97.2% (21,460) were written in English. Other articles were written in French (184), German (114), Spanish (97), Russian (93), Japanese (51), Portuguese (24), Italian (17), Czech (14), Chinese (9), Turkish (7), Polish (5), Dutch (2), Hungarian (2), Serbian (2), Croatian (1), Slovak (1), and Ukrainian (1).
Development of publications
The annual distribution of the 22,084 articles published between 1980 and 2019 is shown in [Figure 1]. The figure also displays the regression analysis results indicating the future predictions of expected publication numbers. According to the regression analysis results, it is estimated that 792 (CI 95%: 709–875) articles will be published in the year 2020 and 891 (695–1087) articles in the year 2028 [Figure 1].
A total of 142 countries had produced publications. The publication distribution of the countries was displayed on the World Map in [Figure 2]. The active countries that produced more than 100 articles were the USA (7362), Japan (2987), the UK (1994), Germany (1812), Italy (1771), France (1492), Canada (991), Spain (880), China (854), Netherlands (621), Switzerland (490), Australia (458), South Korea (431), Belgium (361), India (350), Turkey (343), Sweden (319), Brazil (294), Taiwan (274), Denmark (236), Israel (229), Norway (208), Russia (208), Finland (176), Mexico (175), Poland (175), Austria (159), Hungary (135), Greece (112), New Zealand (107), and Iran (100), respectively [Figure 3].
|Figure 2: The distribution of the most productive countries on the cerebellum|
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|Figure 3: The active countries that produced more than 100 articles on the cerebellum|
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A significant positive correlation was found between the number of articles about the cerebellum and GDP, GDP PPP, and HDI development indicators of the countries (r = 0.743, P < 0.001; r = 0.676, P < 0.001, r = 0.656, P < 0.001, respectively).
The top ten authors who produced the highest number of articles concerning the cerebellum were as fallow; Timmann D (161), Watanabe M (117), De Zeeuw CI (96), Kano M (94), D'angelo E (91), Hawkes R (90), Schousboe A (75), Mariani J (67), Mikoshiba K (58), and Linden DJ (57), respectively.
The organizations and organizations enhanced that produced the highest number of articles on the cerebellum are listed in [Table 1].
|Table 1: Active organizations and organizations.enhanced on the cerebellum|
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Active research areas
In the past 40 years, the top ten research fields of cerebellum studies were found to include as follows: Neurosciences (11383; 51.5%), Clinical Neurology (4425; 20.037%), Biochemistry Molecular Biology (1785; 8.083%), Surgery (1410; 6.385%), Pharmacology Pharmacy (991; 4.487%), Physiology (969; 4.388%), Radiology Nuclear Medicine Medical Imaging (915; 4.143%), Cell Biology (899; 4.071%), Multidisciplinary Sciences (890; 4.030%), and Developmental Biology (819; 3.709%), respectively.
Articles related to the cerebellum were published in a total of 2327 journals. Of them, 52 were published more than 75 articles [Table 2]. The total number of citations and the mean number of citations per article are also given in [Table 2]. In addition, the top 10 most active journals that published the articles on cerebellum topic and the top 10 journals with the most citation per article are presented in [Figure 4]a and [Figure 4]b, respectively.
|Figure 4: (a) The top 10 most active journals that published articles on the cerebellum. (b) Top ten journals with the most citations per article|
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[Table 3] lists the 15 top-cited articles out of the total number of 22,084 articles on the cerebellum. The last column in [Table 3] shows the average number of citations per year.
A total number of 343,238 different publications were cited in the references sections of the 22084 articles. The 10 most-cited publications that received more than 400 citations were the studies conducted by Ito, Lowry et al., Eccles et al., Palay and Chan-Palay, Marr, Schmahmann and Sherman, Albus(1972), Altman, Stoodley and Schmahmann, and Gallo et al., respectively.,,,,,,,,,
Keyword analysis and trend topics
A total number of 25,267 different keywords were used in the 22,084 articles produced about the cerebellum. [Table 4] shows at least 53 keywords used in at least 90 different articles. [Figure 5] displays the cluster analysis performed with 124 keywords used in at least 50 different articles. [Figure 6] demonstrates the network visualization map of the trend keyword analysis in the articles published between 1980 and 2019, the analysis aimed to identify the topic tendency according to the years and potential trends in future. The network visualization map regarding the keyword citation analysis in [Figure 7] aimed to identify the effective topics that received more citations.
|Figure 5: Network visualization map for cluster analysis based on keyword analysis on the cerebellum. Footnote: Six different colors indicate the clustering between the keywords. The size of the circles indicates frequently used keywords. The thickness of the lines indicates that keywords are commonly used together in similar studies|
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|Figure 6: Network visualization map for current trends based on keyword analysis on the cerebellum. Footnote: Indicator shows current publications from blue to red. Keywords in red indicate recently published articles|
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|Figure 7: Network visualization map for the most cited keyword on the cerebellum. Footnote: Keywords in red indicate the most cited keywords|
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| Discussion|| |
In the present study, we investigated global research output on cerebellum over the last 40 years. The results indicated a general increase in the number of publications concerning the cerebellum in the last 40 years. A total number of 310 articles concerning the cerebellum were published in 1980. The number of articles published per year in the 10-year period was between 310 and 387. The number of articles between 1990 and 1995 was 425–498 per year, and the number of cerebellum-related articles notably increased up to 675 in 1996. The total number of articles, which was approximately 566–688 per year between 1996 and 2012 demonstrated a general increasing trend in recent years and has now reached approximately 800. An analysis of the publication trend of the cerebellum-related articles between 1980 and 2020 showed that although there was a slight decrease in the number of articles between 1998 and 2006, a general increasing trend was noted. Parallel to the growing awareness that the cerebellum is involved in many cognitive and emotional processes as well as a wide variety of neurological and psychiatric conditions, there has been a visible increase in the number of publications in the past decade.,, In addition, the contribution of researchers from various scientific fields, ranging from cell biology to neurosciences led to increase in the number of publications in this field., When considering similar publication trend from 1989 to 1993, publication trend predicted for the years from 2020 up to 2028 was expected to continue increasing and reach a total of 891 publications per year by the end of 2028. These results indicated that researchers' interest in the cerebellum topic will also continue to increase in the following years.
An analysis of the publication productivity of the countries with respect to the cerebellum showed that the top 10 most productive countries were primarily the USA and Japan, followed by the UK, Germany, Italy, France, Canada, Spain, China, and the Netherlands. Our results showed that the economic size of countries can be directly associated with publication productivity. This hypothesis is confirmed by the highly significant correlation determined between GDP and GDP PPP and the publication productivity of the countries. The significant correlation between HDI and publication productivity was lower than the correlation between GDP and GDP, PPP and publication productivity. This finding which demonstrates that the economic size of the countries was more effective than the development levels in publication productivity. Bibliometric studies conducted in recent years have also shown that economic size is the most effective factor in publication productivity.,
An evaluation of the journals published articles about the cerebellum showed that the most active journals (i.e., more than 500 articles in total) were the Journal of Neuroscience, Brain Research, Cerebellum, Neuroscience Letters, and Neuroscience. When the total number of citations was considered, the most-cited articles (with more than 15,000 total citations) were published in the Journal of Neuroscience, Proceedings of the National Academy of Sciences of the United States of America, Brain Research, Journal of Physiology London, Journal of Neurochemistry, Journal of Neurophysiology, Journal of Comparative Neurology, Neuron, Neuroscience and Brain, respectively. On the other hand, an evaluation of the journals published articles about the cerebellum according to the number of citations per article and the citation network map showed that the most active journals were the Neuron, Proceedings of the National Academy of Sciences of the United States of America, Brain, Development, Journal of Neuroscience, Journal of Biological Chemistry, Journal of Physiology London, Neuroimage, Neurology, and Annals of Neurology.
As the above-mentioned journals were the most effective and active journals in terms of the number and quality of the articles produced, these journals could be considered a potential source for the researchers specifically interested in the topic of the cerebellum. These journals could be a good guide for planning new studies or projects about the cerebellum, following current qualified studies, and identifying the most appropriate journal address for the completed studies.
Of the 22,084 articles analyzed, the most-cited study was the article entitled “Function of the chemokine receptor CXCR4 in hematopoiesis and in cerebellar development” written by Zou et al. and published in Nature. The authors investigated the role of CXCR4, a chemokines receptor, in hematopoiesis and cerebellum development and reported that this receptor had a critical function in the cerebellar neuronal layer formation during the cerebellum development. The second most-cited article was entitled “Nitric-oxide mediates glutamate-linked enhancement of cGMP levels in the cerebellum” written by Bredt and Snyder and published in the Journal of Proceedings of the National Academy of Sciences of the United States of America. The authors reported that nitric oxide as a messenger molecule mediated the stimulation of cGMP levels in the cerebellum with glutamate.
An analysis of the articles according to the number of citations per year showed that the most-cited study was conducted by Zou et al. Second most-cited article was entitled “The cerebellar cognitive affective syndrome” written by Schmahmann and Sherman and published in the Brain Journal. The third most-effective cerebellum article according to the average number of citations was the study entitled “Marrow stromal cells migrate throughout forebrain and cerebellum, and they differentiate into astrocytes after injection into neonatal mouse brains” written by Kopen et al. and published in the journal of Proceedings of the National Academy of Sciences of the United States of America. The most-cited articles in the references sections of the 22,084 articles were the studies conducted by Ito, Lowry et al., Eccles et al., Palay and Chan-Palay, Marr, Schmahmann and Sherman, Albus(1972), Altman, Stoodley and Schmahmann, and Gallo et al., respectively.,,,,,,,,,
More qualified and effective studies could be produced if researchers interested in the topic of the cerebellum or planning new studies initially review the above-mentioned studies or the other most-cited papers in [Table 3].
According to the keyword cluster analysis findings, cerebellum studies were performed in 6 different clusters which ataxia, Purkinje cell, schizophrenia, development, aging, and apoptosis in cluster centers. The ataxia, Purkinje cell, and apoptosis centered clusters were predominant as the major research clusters.
An evaluation of the analysis results with a view to identifying the trend topics about the cerebellum articles from past to present showed that the most frequently used keywords around 1990 were magnetic resonance imaging (MRI), stroke, granule cell, hippocampus, plasticity medulloblastoma, neurogenesis, cerebellar atrophy, and electron microscopy. The most frequently used keywords around 1995 included rat, oxidative stress and cerebellar ataxia; and the keywords around 2000 were cerebellar granule cell (cells), glutamate, cognition, immunocytochemistry, and in situ hybridization, while the most frequently used keywords around 2005 included motor learning, motor control, apoptosis, aging, neurotoxicity, neuroprotection, GABI, development, mouse, cerebellar cortex, and calcium. The most frequently encountered keywords during the period from 2010 to 2019 included ataxia, posterior inferior cerebellar artery, aneurysm, MRI, functional MRI (fMRI), diffusion tensor imaging, transcranial magnetic stimulation, functional connectivity, cerebellar degeneration, schizophrenia, Parkinson's disease, autism, neurodegeneration, and multiple system atrophy. An analysis of the keywords used in cerebellum studies conducted after 2010 indicated that there was a trend in the cerebellar functional connectivity, cerebellar degeneration, and relationship of the cerebellum with various diseases and the use of the neuroimaging techniques.
When the citation analysis results of the cerebellum articles were evaluated, the most-cited keywords from past to present included motor control, timing, cognition, language, basal ganglia, autism, mouse, synapse, immunocytochemistry, mitochondria, brain-derived neurotrophic factor, N-methyl-D-aspartate, proliferation, cerebral cortex, granule cell, and astrocyte. Since these keywords were in the most-cited studies with a high impact level, it would be beneficial to consider these in planning research on the cerebellum. An analysis of the keywords used in the cerebellum articles to date showed that the cerebellum was included in several disciplines and studies that demonstrated different approaches in terms of topic and content.
As the WoS database indexes only the journals in the Science Citation Index Expanded and Emerging Science Citation Index, it is generally regarded as having more reliability than other databases such as PubMed and Scopus., Therefore, this study did not use databases such as PubMed and Scopus, but only utilized the WoS database.
| Conclusion|| |
The present study is the first attempt to provide a comprehensive analysis of scientific publications regarding the cerebellum since 1980. The study identified the most active countries, collaborations between countries, the journals with the highest number of and most qualified articles in the cerebellum-related publications, the most-cited cerebellum studies, and the most frequently used keywords by years. Recent studies concerning the cerebellum have mostly focused on the cerebellar degeneration, functional connections of the cerebellum and its relationship with various diseases, primarily ataxia, schizophrenia, Parkinson's disease, and autism, aneurysms and the use of fMRI, MRI, and diffusion tensor monitoring. The comprehensive analysis and the findings obtained in the present study, which covered a long period, can be considered to be of value as a good and useful guide for researchers interested in this topic.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]