original research articles that used fMRI with human subjects between 1999 and 2009. We excluded review articles, editorials, meta-analyses and commentaries. A detailed analysis of how we constructed this query is provided in Appendix B in Appendix S1. For the purpose of data management, we retained a randomized subset of up to 200 articles for each year and indexed the articles by their unique PubMed identifier. To obtain metadata on the articles, the articles they referenced, and those in whose reference lists they appeared, we submitted the PubMed identifiers to the Scopus citation database. For both the cited and citing articles, we then identified the subset that contained ELSI content using three filtering criteria. The criteria were developed through both automated and manual analysis of the accuracy and exhaustiveness of their results. At least one of three criteria had to be met for an article to be included (details are provided in Appendix E in Appendix S1): N journal title contained the words or word fragments ‘‘ethic,’’ ‘‘poli-’’, ‘‘philosophy,’’ ‘‘law;’’ or match a list of ISSNs (for journals with less keyword-salient titles), N article title contained the phrase ‘‘informed consent, ’’ or the article title or abstract contain the words or word fragments, ‘‘ethic,’’ ‘‘justice,’’ ‘‘stigmati-,’’ ‘‘responsibil-’’, or ‘‘person- hood’’. N PubMed identifier of the article listed in Scopus and identified by the PubMed ‘‘bioethics[sb]’’ filter. As a final check, we manually reviewed all article titles and abstracts identified by this filtering process and eliminated from further analysis those not considered by the authors to be an article about ELSI issues. We also eliminated citations not considered to reflect substantive discussion of research ethics or ethical, legal, and social implications. This most often occurred when a) a paper in the ELSI literature was cited for a background statistic not related to research ethics or implications, or b) when ELSI papers were cited with respect to the content of the fMRI study – in other words, cited by studies using neuroimaging to study moral, legal, or ethical decision-making. The exclusion of citations referencing these moral correlate studies allowed us to more accurately map citations by fMRI research articles that indicate an additional and substantive engagement in questions arising from the ethics of research or its implications. Note that where a paper with a moral correlates citation also cited an ELSI paper in the context of discussion of research ethics or implications the latter citation was retained. To determine the context of ELSI discussion, we located and retained the paragraphs in which citations occurred. Results 1. fMRI and Neuroethics Publications As illustrated in Figure 1, the prevalence of neuroethics publications has increased by an average of 39% each year since the term was formalized in 2002 [31], but this number is small overall, with 40 publications including the term ‘‘neuroethics’’ in their title or abstract in 2009. However, this does not include those articles that discuss both fMRI and ethics without using the term ‘‘neuroethics’’. Increases in the number of publications considering ethics issues associated with fMRI has risen in turn with those containing an eponymous mention of neuroethics at an average of 51% more publications each year. 2. Landscape of Intersecting fMRI and Ethics Content Of the 134 articles referring to both fMRI and ELSI issues returned by our query, 50 were eliminated for lack of substantial Mapping Neuroethics and fMRI Figure 1. Prevalence of neuroethics publications, 1999–2009. doi:10.1371/journal.pone.0018537.g001 discussion of research ethics. The 84 remaining articles came from a broad range of journals across bioethics, the social sciences, and law. As illustrated in Figure 2, we observed extensive discussion of the forensic, security, and military use of fMRI, frequently in the context of neural correlates associated with guilty feelings or incriminating mental contents of people accused of crimes. In terms of ‘real-world’ implications, this focus on forensic, security, and military use was in marked contrast to the lack of discussion about commercial use, which is arguably the most pressing source of ethical concerns outside the research and clinical context – private imaging clinics already offer scans for lie detection and diagnosis of mental illness [45]. Articles that detailed the extension of neuroscience into legal and other domains often also discussed more general technical problems with generalizing fMRI results across individual human subjects, and from abstract laboratory tasks to real-world contexts. Among the articles discussing both fMRI and ethics, and among ELSI articles citing fMRI articles, there were fewer instances of citations relating to the discussion of classic research ethics issues such as informed consent, incidental findings, working with vulnerable populations, and confidentiality than relating to the implications and limitations of neuroimaging research. Among the fMRI articles themselves, citations of ELSI articles were more evenly distributed among these categories, though the small numbers involved limit the conclusions that can be drawn. It is also of interest that among the fMRI articles citing ELSI articles, the most common context was discussion of technical limitations, concordant with previous observations about the focus of critique in the print media [46]. To provide a more data-driven complement to our qualitative topic analysis, we input the original 134 articles returned by our query into the CiteSpace II platform. Figure 3 illustrates the network resulting for the top cited articles. Each node represents a paper, and the size of the node and of the corresponding label reflects the number of times the paper was cited. The warmth of the node colour indicates the recency of citation: pink indicates the most recent, blue the oldest citations. The distance between the nodes indicates relatedness: if two nodes are close together, the papers they represent share similar content. Clusters of closely- related papers are indicated by free-form blue shapes. Their citation centre of mass is shown by the blue circle. The salient neuroethics terms used to translate the machine-derived labels for each cluster were: decision making, cognitive enhancement, personhood, incidental findings, legal implications, minimally conscious states, truth telling, and the term ‘‘neuroethics’’ itself. It is important to note that the 77 nodes in this network do not correspond exclusively to articles from the 134 articles originally PLoS ONE | www.plosone.org 3 April 2011 | Volume 6 | Issue 4 | e18537