|Year : 2019 | Volume
| Issue : 4 | Page : 196-207
An overview of transcranial magnetic stimulation research with bibliometric Indicators
Shafiq Ahmad1, Moath Alatefi1, Ali Hamza2, Shahid Bashir3
1 Department of Industrial Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia
2 Department of Electrical Engineering, National University of Computer and Emerging Sciences, Lahore, Pakistan
3 Department of Neurophysiology, Neuroscience Center, King Fahad Specialist Hospital Dammam, Dammam, Saudi Arabia
|Date of Web Publication||4-Oct-2019|
Department of Neurophysiology, Neuroscience Center, King Fahad Specialist Hospital Dammam, Dammam
Source of Support: None, Conflict of Interest: None
Transcranial magnetic stimulation (TMS) is a noninvasive technique increasingly used in basic and clinical research practices around the world. Its established clinical applications include treatment of major depression and presurgical functional mapping of the motor and language cortexes. In experimental and clinical trials have aimed to test the therapeutic and diagnostic utility of TMS in a range of disease states, including obsessive–compulsive disorder, schizophrenia, autism, strokes, tinnitus, Alzheimer's and Parkinson's diseases, traumatic brain injury, multiple sclerosis, migraine, and dystonia. To quantitatively analyze the current worldwide progress in TMS research based on the Web of Science (WoS) database for the past 27 years. We conducted a quantitative analysis of articles regarding TMS that were published in English between 1988 and 2015 and that were indexed in the WoS database. In the past 27 years, there have been 14,077 studies on TMS indexed by the WoS database. The analysis results indicate that most of the research studies in the field were published by North American and European institutions. With respect to Asian countries, Japan also published a reasonable proportion of publications, but comparatively speaking, the number of publications is rare. From the perspective of research progress, we found that the number of published articles on TMS has increased significantly in the past 10 years.
Keywords: Bibliometric analysis, rehabilitation, reviews, transcranial magnetic stimulation, treatment, Web of Science
|How to cite this article:|
Ahmad S, Alatefi M, Hamza A, Bashir S. An overview of transcranial magnetic stimulation research with bibliometric Indicators. J Nat Sci Med 2019;2:196-207
|How to cite this URL:|
Ahmad S, Alatefi M, Hamza A, Bashir S. An overview of transcranial magnetic stimulation research with bibliometric Indicators. J Nat Sci Med [serial online] 2019 [cited 2019 Oct 22];2:196-207. Available from: http://www.jnsmonline.org/text.asp?2019/2/4/196/260446
| Introduction|| |
Transcranial magnetic stimulation (TMS) is a neurostimulatory technique used in clinical and research practices around the world. In 1831, Michael Faraday showed that a rapidly changing magnetic field could induce an electrical current in a nearby conductor. During the following years, scientists explored the great potential of electromagnetic induction. At the beginning of the 20th century, scientists started to apply this principle to nervous tissue and ultimately, the human brain. The development continued consistently, and in 1980, scientists Merton and Morton showed that it was possible to stimulate motor areas of the human brain through the intact skull.
However, they used direct current stimulation, which was very uncomfortable for the patients. By using TMS over the vertex of the human brain, Barker et al. were able to successfully elicit a motor response of hand muscles without negative effects to the patients. TMS, as we know it today, was first presented at the London Congress of the International Federation of Clinical Neurophysiology in 1985 by Anthony Barker as a noninvasive technique for brain stimulation. This method became well established in neuroscientific research, as clearly shown by the steadily increasing number of TMS articles published in peer-reviewed journals. Nowadays, TMS is extensively used not only in basic research, but also in clinical neurophysiology, including rehabilitation and intraoperative monitoring. The recent integration of TMS with imaging techniques extends the possibilities of TMS even further. For instance, the combination of TMS with structural and functional magnetic resonance imaging allows the orientation and navigation of TMS over the human cortex (neuron navigation) and provides the means for a relatively precise mapping of a given body representation in the motor cortex.
Therefore, TMS and its integrated techniques offer new and inspiring possibilities for rehabilitation and treatment. Additional TMS protocols enable us to investigate different neurophysiological processes. For instance, paired-pulse TMS (two consecutively applied TMS pulses) can be used to evaluate excitatory/inhibitory intracortical circuits and thus provide information on brain physiology and pathophysiology of various neuropsychiatric diseases. This method can also be used to investigate the mechanisms of brain plasticity and the effects of neuroactive drugs on neural excitability. Besides single-pulse TMS, several other TMS protocols have been established; for instance, repetitive TMS (rTMS) using fast, repeating pulses for a given length of time. With this protocol, the target area shows lasting changes in neural excitability in the range of 10–30 min. Being able to induce long-lasting changes in neural excitability opened the possibility for TMS to treat neuropsychiatric diseases that are based on brain excitability dysfunctions. In this review, we illustrate the currently used TMS protocols and outline the recent TMS studies that use these protocols for rehabilitation and treatment of neurological disorders. The interesting opportunities of TMS for research, rehabilitation, and treatment, however, need careful consideration before applying it to participants and patients. There are some limitations of TMS that need a high level of attention and will be described here in detail. There is a great deal of evidence depicting the benefits of clinical applications of TMS. In this review, we focus on recent developments, but also agree that a lot more research needs to be conducted in order to design efficient treatment protocols.
The therapeutic utility of TMS has been claimed in the literature for many psychiatric disorders such as depression, acute mania, bipolar disorders, panic, hallucinations, obsessions/compulsions, schizophrenia, catatonia, posttraumatic stress disorder, and drug cravings. Further, many neurologic diseases have been described to benefit from TMS such as Parkinson's disease, dystonia, tics, stuttering, tinnitus, spasticity, epilepsy, rehabilitation of aphasia, recovering hand functions after stroke, and pain syndromes, such as neuropathic pain, visceral pain, or migraines. A large industry-sponsored trial  and a multicentric trial in Germany using rTMS in addition to medication for refractory depression have been completed. Other well-controlled and sufficiently powered TMS clinical trials are still under investigation and ongoing.
Although originally developed as a diagnostic tool, TMS can transiently or lastingly modulate cortical excitability via the application of localized and, at times, repetitive magnetic field pulses. This and other neurobiological effects can be leveraged for therapeutic applications in neurology, psychiatry, and rehabilitation.
Because TMS has received significant attention by researchers and professionals around the globe, it is worth analyzing the published TMS research material to understand the latest developments and identify the leading trends. To accomplish this, a bibliometric approach is applied to quantitatively analyze the bibliographic material. This methodology can be deployed in a wide range of contexts to identify bibliometric indicators, such as influential journals, authors, institutions, and countries, contributing significantly to the TMS field, including analyzing a research topic and the author's keywords. Citation searching and bibliometric methods measure resources to rank and track institutions  and countries. There are a number of bibliometric studies that have been published recently that are close to the scope of TMS, including health economics and health sciences publications.,
Motivated by this, the aim of this article is to provide a bibliometric overview of the TMS research conducted specifically between 1988 and 2016. The analysis considers a wide range of issues, including the publication, citation structure of the journal, the most-cited articles, the most influential authors, institutions, and countries. By doing so, we can observe the leading contributors to the TMS research field and also its main trends that have influenced it more recently.
The rest of the report is structured as follows: Section 2 briefly reviews the bibliometric methods used in the analysis. Section 3 presents the results and analysis comprising a publication and citation structure analysis as well as a trend analysis of TMS. Influential and leading articles are discussed in Section 4. Sections 5 and 6 present the bibliometric analysis of leading journals, authors, institutions, and countries followed by a summary and the conclusion of the report in Section 7.
| Bibliometric Methods|| |
Given the progressively increasing interest in clinical and experimental use of TMS, we collected data on TMS from the Web of Science (WoS) database to measure international research trends in TMS over the past 27 years. Assuming that TMS research trends are represented in publications, we focused on citation rate as a direct measure of the impact that an author, institution, or group of institutions have on the field., A popular research analytics approach applied for this kind of study is referred to as the bibliometric method, which has been widely applied in almost all science and engineering disciplines in recent years.
From 1985 to 2015 in the TMS research literature are selected as highly cited articles and then analyzed with regard to the total number of publications and citations, the citations per publication, the h-index,, the citing articles, and citation threshold citation histories. Highly cited articles with address information of both the first and corresponding authors were also analyzed using an h-index, which is applied to evaluate the contributions of individual authors and institutions.
The h-index combines publications with citations. So that the set of publications with H-index value of x“, it means that there are x publications inside this set of publications that have received x citations or more. For instance, if we select a set of articles with an h-index of 15, it means that 15 articles considered in the selected set have obtained at least 15 citations for each article. The citing articles are those articles that cite the material considered in the analysis. The citation thresholds considered in the study analyze the number of articles above a specific number of citations.
This work uses the WoS database managed by Clarivate Analytics. Particularly, we use the WoS Core Collection that indexes the documents that are usually recognized as having the highest quality. The WoS currently indexes more than 15,000 journals and more than 50 million documents. As keywords, we used “transcranial magnetic stimulation” with the search option “Topic.” The search considers all the documents published between 1988 and 2015.
| Results and Discussions|| |
TMS publications' growth is depicted in [Figure 1], which shows the evolution of the number of articles published annually during the selected period with respect to the total publications (TPs) reported by the WoS. The total number of publications has increased steadily since 1991. The number of articles has increased exponentially from 1999 when it started to stabilize more than 200 articles per year.
|Figure 1: Number of annual publications in TMS research (articles + reviews) since 1988. The orange bars indicate the total number of TMS articles published each year in the WoS and the blue bars indicate the ratio (N-TMS-P/TNP) ×1,000,000 where N-TMS-P is the number of the publication on TMS in WOS in year n, and TNP the is the total number of publication in all science in web of science in year n. TMS: Transcranial magnetic stimulation, WoS: Web of science|
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Further, after analyzing the citations received by the TMS research articles published in scientific journals throughout the selected period of time, the results indicated that the TMS citation index also increased statistically significantly (P = 0.003), which follows a strong growth path every year (Yt = 3756.34 × [1.10339^t]), as shown in [Figure 2]. As the number of research journals increased worldwide in the past decades, this also has a positive effect on citation growth. It is worth mentioning that the data obtained from WoS are dynamic and will change in future as published TMS articles receive more citations.
[Table 1] presents the citation structure showing which TMS published articles have received citations in the WoS for each year. Note that the citation thresholds indicate the number of articles published in a specific year that have surpassed a number of citations. In [Table 1], it is worth noting that a bit more than 1% of the articles have received more than 250 citations, about 9.99% have received at least more than 50 citations, and 83% of the articles have received more than 10 citations.
|Table 1: General citation structure in transcranial magnetic stimulation research in the Web of Science|
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| Influential and Leading Articles|| |
Furthermore, [Table 2] presents the forty most-cited articles in the field of TMS [Appendix 1]. The highly influential article published in the Journal of Physiology London in 2000 by Nitsche and Paulus has received the highest number of citations (1401). In their study, they analyzed TMS excitability changes induced in the human motor cortex using weak transcranial direct current stimulation. Rizzolatti and Arbib  had the second highest and Gandevia the third most-cited articles. Rossi et al. had the fourth and Corbetta et al. had the fifth most-cited paper.
|Table 2: Forty most cited articles in transcranial magnetic stimulation research of all time|
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Further taking into account the yearly citation index (C/Y) in [Table 2], the articles by Rossi et al. (R = 4) received the highest number of citations (176) in 2009 followed by Corbetta et al.'s article (R = 5) in 2008, which received 146 citations. The other two most-cited articles (R = 7) are by Huang et al. and by Park et al. (R = 15), having received 97 and 95 citations, respectively.
| Leading Journals|| |
Further, a most active and productive journal analysis was conducted. The top thirty journals were selected based on the criterion of the h-index and are listed in [Table 3]. It also provides extensive information about the number of publications, citations, and the h-index in the TMS field as well as the total number of published articles in their respective journals. Brain(B) journal is the topmost productive and influential journal based on the h-index criterion. It obtained the highest h-index (82) followed by the Experimental Brain Research (EBR) journal, with h-index of 76. The third, fourth, and fifth ranked journals are Clinical Neurophysiology (CN), Journal of Neurology (N), and Journal of Neuroscience (JN), with h-indexes of 73, 71, and 70, respectively. The Journal of Clinical Neurophysiology (JCNP), although ranked third based on the h-index criterion, it has obtained the highest number of citations (24,245) among the top thirty selected journals. To highlight the journal's contributions toward publishing TMS research, [Table 3] also contains a column (%TP) showing the percentage of articles on TMS published in a journal with respect to the total number of articles in all other areas in the same journal in the selected period. For instance, B has published 195 articles in the TMS field, whereas its TPs in all other areas are 9809, so the %TP will be obtained by 100 (195/9809) =1.99. According to the %TP indicator, the Brain Stimulation Journal again ranked at the top (39.95) followed by Clinical Neurophysiology (12.07%) and Restorative Neurology and Neuroscience (8.81%).
|Table 3: Most influential journals in transcranial magnetic stimulation research|
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The citation structure of TMS research is also presented in [Table 3] [Appendix 1]. It is worth noting that journals B and Journal of Neurophysiology have three articles with more than 500 citations. Brain Journal has 57 articles that have received more than 100 citations, while EBR and CN that published more than 80 articles obtained more than 50 citations. It is also worth noting that the journal JN has the highest h-index (433) among all the publications, with the highest number of citations (2,511,583).
| Leading Authors, Institutions, and Countries|| |
In recent years, the TMS research field has become popular and has attracted many authors, institutions, and countries worldwide. To highlight their contributions toward this field, the data were analyzed to figure out the most productive and influential authors. [Table 4] presents the fifty most influential authors in the TMS field who published their research work throughout the selected period of this study.
|Table 4: The most productive authors in transcranial magnetic stimulation research|
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Thus, the ranking criterion in [Table 4] is according to the number of TMS articles published by each author. Only those authors who have published at least fifty articles in TMS were considered. Pascual-Leone A is the author that has received the highest rank (TPs = 325) based on his articles published in the TMS field. Rothwell JC appears in the second position (TPs = 320) as one of the most influential authors (TC = 22,817) in TMS. It is also worth noting that Hallett M and Cohen LG have published 211 and 192 articles among the fifty most cited in the TMS, respectively. Note that these first four authors are very highly cited, particularly Rothwell and Hallet, who have more than 50,000 and 70,000 citations, respectively, in the WoS for their whole publications. This implies that they are highly ranked worldwide. Note that some other highly cited researchers also have significantly influenced the TMS, including Fitzgerald PB, Paulus W, Ziemann U, Daskalakis ZJ, Rossini PM, Fregni F, Chen R, George MS, and Walsh V. It is worth noting that Chen R ranked at the 11th position (TPs = 140) in the TMS research, but in the WoS, in all areas, he is the topmost productive (TPs = 18,709) and influential (TC = 261,602; h-index = 182) author among the selected top fifty authors in the TMS research field. It is further interesting to note that approximately 90% of the authors belong to the Western countries, as shown in [Table 4].
Next, the top ten influential authors were clustered according to the ten selected journals that have significantly contributed to the TMS field. The cluster in [Figure 3] presents valuable information such as the number of clusters, authors existing in the same cluster, and how the clusters are related to each other. For example, Fitzgerald PB, Daskalakis ZJ, and Fregni F exist in the same cluster, and this cluster is related to the cluster containing Paulus et al., and Hallett M exists in more than one cluster.
Next, we analyze the bibliometric data for the productive institutions worldwide. In recent years, a number of institutions contributing to the TMS research field are increased. Some of them have significant influence and played a leading role in TMS research. Usually, the leading institutions in any research area are those where the leading authors and researchers are employed and retained. However, sometimes, there are institutions that include a wide range of leading researchers and authors, making them more influential. [Table 5] shows the topmost fifty productive institutions in TMS research. The criterion for ranking them is their productivity and contributions with the number of publications in the TMS field. The results show that the University of London is a highly productive (TPs = 960) institution followed by University College London (TPs = 823). Harvard University is ranked third in the selected list, with 650 publications, followed by National Institutes of Health (NIH) USA, which has published 556 publications.
|Table 5: The most influential institutions in transcranial magnetic stimulation research|
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[Table 5] also summarizes the country of authors, the number of citations, and the h-index. The NIH USA obtained the most remarkable results, with an h-index of 120, and ranking the topmost position in the selected list of institutions. In addition, it is worth noting that most of the institutions contributing to TMS research belong to the USA, Germany, and the UK.
After classifying authors and institutions by countries in [Table 4] and [Table 5], another interesting issue is to consider country's contributions in TMS research and analyzing the regions where TMS is more influential. To do this, [Table 6] summarizes the thirty most productive and influential countries in the TMS research field. The countries are ranked by productivity, although some other indicators including the citations and their influence by citations per country are also considered. The temporal evolution of the publications of the 30 selected countries that appeared in the selected period of this study is depicted in [Table 6].
|Table 6: The most influential countries in transcranial magnetic stimulation research|
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The USA, Germany, and Italy are the leading countries with a total number of publications of 3852, 2456, and 2027, respectively, in the TMS. Next is England, which is ranked fourth in the number of publications (TPs = 1835); however, it stands out at the third position in obtaining the total number of citations (TC = 81,855), the second position in h-index (134), and the first position in the total number of citations for publications in the last 10 years (TC10=81,855). Canada, Australia, and Japan also contribute significantly with the total number of publications of 1155, 1090, and 933, respectively, in this field.
| Conclusion|| |
This study has provided a quantitative overview of TMS research. It has discussed different research indicators that will help interested readers comprehend the overall progress and trends in the TMS research field based on bibliometric data. The study has revealed that TMS research is active and getting more and more attraction worldwide by researchers and professionals in recent years. The main objective of this research study was to reveal useful information about the TMS field and to summarize useful bibliometric indicators from the studies reported in this field. From this study, the main conclusions could be inferred were as follows: the USA is the most influential country in the TMS research, followed by Germany and Italy. England seems to be the most active country in the last 10 years, with the highest number of citations. Among the topmost journals, B appeared to be the most productive and influential journal in the list, followed by EBR. Journal of Clinical Neurophysiology obtained the highest number of citations among the selected journals. Among most productive and influential authors, Pascual-Leone is the first, followed by Rothwell JC, who is also the most influential author with the highest number of citations in TMS. It is interesting to note that most of the authors belong to English-speaking countries; however, Chen R from China appeared the most productive and highly influential author in the WoS among the selected list of top fifty authors who contributed significantly in the TMS research field. Among institutional analysis, the University of London is highly productive, followed by University College London. Harvard University is ranked at the third position. It is also interesting to note that the NIH USA obtained the highest h-index among all the institutions. This study has also revealed that some institutions from new countries also appeared on the list, including Japan, China, South Korea, Brazil, Israel, Turkey, India, and Egypt. Currently, their contributions are not in highly significant positions, but in future, it is expected that they will continue growing significantly to reach similar results as the current top countries and institutions have achieved.
The authors extend their appreciation to the Deanship of Scientific Research at King Saud University for funding this work through research group no. RG-1438-089.
Financial support and sponsorship
This study was financially supported by the Deanship of Scientific Research at King Saud University through research group no. RG-1438-089.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]