ARTICLE Methodological guidelines to investigate altered states of consciousness and anomalous experiences Alexander Moreira-Almeida a and Francisco Lotufo-Neto b a Research Center in Spirituality and Health (NUPES), School of Medicine, Federal University of Juiz de Fora (UFJF), Juiz de Fora, Brazil; b Department of Psychiatry, School of Medicine, University of S~ ao Paulo (USP), S~ ao Paulo, Brazil ABSTRACT Anomalous experiences (AE) (uncommon experiences or one that is believed to deviate from the usually accepted explanations of reality: hallucinations, synesthesia, experiences interpreted as telepathic … ) and altered states of consciousness (ASC) have been described in all societies of all ages. Even so, scientists have long neglected the studies on this theme. To study AE and ASC is not necessary to share the beliefs we explore, they can be investigated as subjective experien- ces and correlated with other data, like any other human experience. This article presents some methodological guidelines to investigate these experiences, among them: to avoid dogmatic prejudice and to ‘pathologize’ the unusual; the value of a theory and a comprehensive literature review; to utilize a variety of criteria for pathology and normality; the investigation of clinical and non-clinical populations; development of new appropriate research instruments; to be care- ful to choose the wording to describe the AE; to distinguished the lived experience from its interpretations; to take into account the role of culture; to evaluate the validity and reliability of reports and, last but not least, creativity and diversity in choosing methods. KEYWORDS Methodology; altered states of consciousness; spirituality; anomalous experience; science; research Introduction The term ‘anomalous experience’ (AE) is employed to designate an uncommon experience (e.g. synesthesia), or those, even being reported by many people (e.g. experiences interpreted as telepathic), they are believed to be different from the usual as well as from the usually accepted explanations of reality. AE do not necessarily relate to pathology or abnormality (Carde~ na, Lyinn, & Krippner, 2000). Closely related to the AE are the ‘altered states of consciousness’ (ASC), which Charles Tart (1972, p. 1203) defined as ‘a qualitative alteration in the overall pattern of mental functioning, such that the experien- cer feels his consciousness radically different from the way if functions ordinarily’. The same author makes an analogy between the changing from an usual state of consciousness to an ASC, describing [comparing] that the same computer can function with two differ- ent programs. In this situation, the same set of data or information may be processed through much dif- ferent ways and generate greatly diverse out puts. Although there is overlapping between AE and ASC, the previous may happen during usual states of consciousness (e.g. hallucinations). AE and ASC have been reported in all civilizations throughout ages, many times playing an important role in the history of societies and, especially, of their religions (e.g. Delphi oracle, Socrates hearing his dai- mon's advices, Moses, Saint Paul, Mohamed etc). It has a profound impact, either in the lives of those who experience it directly and in the lives of those who are indirectly affected. The religious and the spir- itual dimensions of the culture are between the most important factors shaping the faith, the values, the behavior and the pattern of human illness, in sum- mary, the human experience (Lukoff, Lu, & Turner, 1992). Dissociative experiences very frequently happen in religious/spiritual contexts, many times as ASC. Despite being specific concepts, AE, ASC, religious and dissociative phenomena are so closely intercon- nected that we are going to refer to them in a manner more or less interchangeable in this paper. Frequently, scientific papers have considered such experiences as rare phenomena, vestiges of ‘primitive Cultures’ or indicators of psychopathology (Freud, 1969; Horton, 1974; Mulhern, 1991; Munro & Persinger, 1992; Persinger, 1992; Greenberg et al., 1992). However, population surveys have CONTACT Alexander Moreira-Almeida alex.ma@ufjf.edu.br School of Medicine, Federal University of Juiz de Fora, Av. Eug^ enio do Nascimento s/n  - Dom Bosco, 36038-330 Juiz de Fora, MG, Brazil ß 2017 Institute of Psychiatry and John Hopkins University INTERNATIONAL REVIEW OF PSYCHIATRY, 2017 VOL. 29, NO. 3, 283–292 http://dx.doi.org/10.1080/09540261.2017.1285555