Illusory perceptions of the human body and self

Illusory reduplication of the patient’s own body refer to complex manifestations during which human subjects experience a second own body or self in their environment. Here we refer to this illusory second own body or self as a double. Doubles may be seen, felt, or heard, may be multiple or even concern the inner organs of the patient. Doubles have fascinated mankind from time immemorial and – often under the term autoscopic phenomena – several distinct forms have been described that can be separated based on phenomenological, functional, and anatomical criteria. The main forms of doubles are the visual own-body reduplications: autoscopic hallucination (AH), heautoscopy (HAS), and out-of-body experience (OBE) as well as the rarer forms including polyopic heautoscopy and inner heautoscopy. These are referred to here as visual doubles. Other own body reduplications include feeling of a presence (sensorimotor doubles), hearing of a presence (auditory doubles), and negative heautoscopy (negative doubles). Doubles are abundant in folklore, mythology, and spiritual experiences (Rank, 1925; MenningerLerchenthal, 1946; Todd and Dewhurst, 1962; Sheils, 1978; Arzy et al., 2005; Metzinger, 2005). In more recent times, doubles became a frequent and popular topic in the romantic literary movement of the nineteenth century (Rank, 1925; Dewhurst and Pearson, 1955; McCulloch, 1992). Reflecting these popular trends, detailed case descriptions (Muldoon and Carrington, 1929; Yram, 1972; Alvarado, 1992) and medical reports (Du Prel, 1886; Féré, 1891; Sollier, 1903a) began to appear. Since then, doubles have been repeatedly described in patients suffering from neurological or psychiatric disease (Menninger-Lerchenthal, 1935; 1946; Lhermitte, 1939; Hécaen and Ajuriaguerra, 1952; Todd and Dewhurst, 1955; Lukianowicz, 1958; Leischner, 1961; Fredericks, 1969; Devinsky et al., 1989b; Grüsser and Landis, 1991; Dening and Berrios, 1994; Brugger et al., 1997). Doubles have been related to various neurological diseases such as epilepsy, migraine, neoplasia, infarction, and infection (Menninger-Lerchenthal, 1935; 1946; Lippman, 1953; Devinsky et al., 1989a; Grüsser and Landis, 1991; Dening and Berrios, 1994; Brugger et al., 1997; Podoll and Robinson, 1999) and psychiatric diseases such as schizophrenia, depression, anxiety, and dissociative disorders (Menninger-Lerchenthal, 1935; Lhermitte, 1939, Bychowski, 1943; Hécaen and Ajuriaguerra, 1952; Todd and Dewhurst, 1955; Lukianowicz, 1958; Dening and Berrios, 1994; Simeon, 2004; Bünning and Blanke, 2005; Mohr and Blanke, 2005). Yet, despite this large number of observations of doubles in neurological disease they occupy a neglected position in neurobiology and behavioral neurology.