ways [16]. The movement of fMRI research into media reports and real-world applications is also deeply entangled with the researcher’s activities, contra assertions that research is neutral to whatever might be made of it. The nascent field of neuroethics aims to highlight, inform, and address underexplored ethical, legal, and social issues arising from neuroscience, and to encourage discussion among researchers and research communities [30–33]. Here we ask whether neuroethics has been successful in penetrating the neuroimaging research domain by examining citation patterns. Investigating bibliometric trends such as citation patterns is a key method for understanding the development of nascent fields such as neuroethics and their interaction with existing disciplines, and for tracking the evolution of their often mutable terminologies [34]. One might predict that primary research articles would not discuss (neuro)ethics in depth, with researchers assuming that institutional ethics approval is sufficient, and having little incentive to engage further [35–36]. This is of concern, as ethics training and approval is often superficial and inadequate to the particular quandaries of neuroimaging [5]. However, one might also expect that the increasing degree of overlap between the potential real- world implications of fMRI research and its subject of study – for example, in experiments pertaining to human nature, mental contents, and moral reasoning – would be reflected in increased overlap in fMRI and ethics content, and in cross-citations between the two literatures. In addition, there have already been calls for researchers to engage more deeply in ethical, social, and legal debate within science journals [33,37], neuroethics topics are increasingly discussed in the popular press [38,39], and neuroi- magers are increasingly called upon to defend their encroachment on the traditional domains of the humanities [40,41]. Methods For bibliometric methods to accurately describe the shape of a particular field, it is crucial that search strategies, inclusion criteria, and visualization practices are appropriate to the domain [42]. We therefore developed the methodological procedure described below through collaboration between experts in information science, scientific publication, neuroimaging, and neuroethics. Full details are included in Table 1 and in the Appendix S1. 1. Tracking Overlapping fMRI and Neuroethics Publications We took as a starting point Seixas and Basto’s (2008) bibliometrics analysis of neuroethics, the only other study of this nature to date [43]. Although Seixas and Basto’s (2008) focus was on impact factor and nation of origin, and on issues affecting radiologists [43], we revisited their coding guide to provide continuity for the present content analysis. We conducted searches Table 1. Research Questions and Data Sets. Mapping Neuroethics and fMRI for all articles indexed in PubMed containing permutations of the phrases ‘‘functional magnetic resonance imaging,’’ and ‘‘ethics,’’ as well as all literature containing the term ‘‘neuroethics’’ specifically, and recorded publication numbers for each year (see Appendix A in Appendix S1). 2. Mapping the Intersection of fMRI and ELSI We used an ISI Web of Science query to identify scholarly articles published between 1999 and 2009 that contain both ‘‘fMRI’’ and ‘‘ethical’’ or ‘‘legal’’ as topic terms (see Appendix B in Appendix S1).We discarded all articles that did not have abstracts available and ‘false hits’ (articles in which the mention of ELSI was non-substantive, e.g., a cursory reference without any discussion within the text, or referred to a standard ethics approval process). We sorted the remaining articles according to nominal topic categories, augmenting the scheme used by Seixas and Basto (2008) to reflect new facets of the literature [43]. Appendix C in Appendix S1 lists the categories in the original and augmented coding scheme – the only two independent additions were a category including research on the neurobiology of moral and ethical judgments, and a meta-ethics category to encompass papers and reviews considering neuroethics itself. A final coding scheme was applied by two authors (LW and AG), and the minimal number of disagreements were resolved through discussion. Since this kind of coding is inevitably shaped by pre-existing ways of conceptualizing the literature, both in the design and application of the codes, we also conducted an automated analysis to reveal clusters of co-citing papers. This provides a more data-driven picture of ELSI topics surrounding fMRI, weighted by a richer measure of the prominence of each paper in the citation landscape. We submitted the original query results to the CiteSpace II platform for visualizing patterns in Scientific Literature, which generates an directed graph showing the citation links (edges) between papers (nodes, each representing a single published article) [44]. Less well-connected papers were filtered out using a standard pruning procedure to aid visualiza- tion. This procedure is described in detail in Appendix D in Appendix S1. We also used the CiteSpace II platform to apply machine- derived labels to each cluster, constructed from noun phrases appearing in the constituent article titles, abstracts, and indexing terms. Such machine-derived labels are seldom a close approxi- mation of natural scientific language, and we therefore translated the machine-derived labels into more salient terms already utilized in the neuroethics literature. This translation process was evaluated by a team with expert knowledge of the domain. 3. Citation Analysis To specifically investigate direct citations between articles from the two domains, we constructed a PubMed query to identify Research Questions Data Set Is discussion of the ethics issues surrounding fMRI taking place, and if is it described using the term ‘‘neuroethics’’? Academic papers containing permutations of the phrases ‘‘functional magnetic resonance imaging,’’ ‘‘ethics,’’ ‘‘neuroethics’’ Source: PubMed. What are the salient topics among articles discussing both fMRI research and ethical, legal, and social issues? Academic papers containing permutations of the phrases ‘‘functional magnetic resonance imaging,’’ ‘‘ethics,’’ ‘‘legal’’ (see Appendix S1). Source: ISI Web of Science. Are fMRI articles, and those discussing ethical, legal, and social issues, citing each other? doi:10.1371/journal.pone.0018537.t001 Original fMRI research articles, based on detailed machine-derived query and manual curation. Source: PubMed. ELSI research articles, based on detailed query. Source: Scopus. PLoS ONE | www.plosone.org 2 April 2011 | Volume 6 | Issue 4 | e18537