Mapping Neuroethics and fMRI Figure 2. Content analysis of neuroethics publications and citation contexts. doi:10.1371/journal.pone.0018537.g002 extracted from the ISI database. Article nodes were incorporated based on a high degree of relatedness to the topic clusters, including any highly cited articles not part of the original data set. The only such article on our graph is the 1972 Lancet article in the personhood cluster. The large mass in the center describes research into moral correlates, including fMRI studies of personhood, disgust, and racial bias. While this largest cluster contains at least one citation link out to every other cluster on our graph, it overlaps most heavily with articles considering legal implications. This related- ness between the neuroscience of ethics and its applicability to the law was thus observed in both our manual coding and the cluster analysis, and reflects the presence of discussion about the legal implications of fMRI in both the popular media and legal press [39,46–47]. Articles about incidental findings and cognitive enhancement form relatively cloistered clusters. The most highly-cited and interconnected node in each cluster represents one of the earliest papers in the respective domain: respectively, Kim et al. (2002), discussing incidental findings in pediatric MR imaging [48], and Anderson et al. (1999) discussing the implications of early prefrontal cortex damage [49]. The connection between prefrontal cortex damage and cognitive enhancement may not be immedi- ately obvious: brain injury in fact provides a striking context in which interventions are made to enhance cognitive or behavioral ability [50]. An eponymous neuroethics cluster also emerged, describing those articles judged most similar purely for their use of the term, and often arising in the context of early commentaries on the state and aims of the discipline [e.g., 51]. Overlapping with this cluster were those labelled ‘‘personhood’’ and ‘‘minimally conscious states’’, suggesting that these domains are most closely associated with the neuroethics literature; future work could investigate the chronology of this interaction. Topics such as the diagnostic and predictive potential of fMRI are more pervasive and less effectively clustered, perhaps reflecting their methodological generality and reminding us that ELSI issues associated with fMRI span technical, research, academic, and applied domains. 3. Citation Analysis 3.1 Citations of the Ethics literature. To explore the degree of co-citation between the fMRI and ELSI literatures, we retrieved 3,484 fMRI articles published between 1999 and 2009. The automated ethics filter selected an initial subset of 244 ELSI articles cited by the fMRI articles (see Section 2.3; Figure 2). Of these, we manually identified 137 as research articles investigating the neurobiology of moral or ethical behavior, leaving 107 articles concerned with fMRI research ethics or implications. We examined the citation context of the remaining 107 articles, yielding only 18 citations that took place as part of a substantive ethics discussion in an fMRI article. However, this very small proportion does appear to be increasing from a baseline of virtually zero, at an average rate of 22% per year over the last ten years. The quotes below are illustrative examples of the citation contexts in which fMRI articles invoked ELSI articles as part of a substantial ethics discussion: ‘‘If lawyers and ethicists continue to debate whether lesion patients or psychiatric patients with functional deficits should be considered culpable for their immoral actions [50], it will be helpful to acknowledge that some brain regions might be involved in only specific subsets of moral processing because patients could conceivably be held culpable for some types of immoral actions but not for others. Although there is still much to explore, the data reported here lay the groundwork for many future interdisciplinary investigations’’ [52]. ‘‘This has led to concerns that some [minimally conscious patients], who retain an awareness of self or environment, are being ‘warehoused’, without adequate access to appropriate assessment or rehabilitation’’ [53]. ‘‘Even during this period of expanded application, examiners have cautioned that appropriate use of fMRI in special samples will require further investigation of the influence of cerebrovascular changes on the fMRI signal’’ [54]. 3.2 Citations of the fMRI literature. Of the articles citing the 3,484 fMRI articles selected, 43 articles published across varied disciplines such as law or business ethics included a substantial discussion of research ethics or ELSI implications meeting our criteria. These increased over time at a greater rate than the citations of ELSI literature in fMRI, at an average rate of 36% per year over the last ten years. Many of the citations of fMRI articles in the ELSI literature occurred in the context of PLoS ONE | www.plosone.org 4 April 2011 | Volume 6 | Issue 4 | e18537