Léon Dénizarth Hippolyte Rivail (1804–1869) is best known by his pen name Allan Kardec and as the spiritual father of Spiritism—to be differentiated from Spiritualism. Less known is the fact that Kardec was a member of several learned societies, including the Royal Academy of Arras, which crowned him for an outstanding memoir on didacticism in 1931. Kardec was a teacher by vocation and produced several pedagogical works in Mathematics, Grammar, Chemistry, Astronomy, Physics and Physiology.
Initially, a sceptical and materialist, Kardec researched the phenomena of Spiritism formulating and testing several critical hypotheses that could explain communications with Mediums. However, through a carefully applied methodology, Kardec became convinced that such communications were not the product of fraud, hallucinations, somnambulism, or unconscious self-suggestion  but were true communication with spirits .
Much less known is the fact that his first book, Le Livre des Esprits (The Spirits' Book), launched on the 18th of April of 1857, consisting of 1019 questions asked to Spirits, was one of the first enquiries of the Second Industrial Revolution era to research the different aspects of the "separation of the soul and body" at the time of death and the "emancipation of the soul during physical life", composing two entire sections of the book. More specifically, the notion that Out-of-Body Experiences (OBEs) are manifested through dreams:
"The freedom of the soul, during sleep, is manifested during the phenomenon of dreams. Dreams are thus the product of the soul's emancipation, rendered more independent by the suspension of active life and relationships. From there, a kind of undefined clairvoyance extends to the most distant places; some we have never seen, and sometimes even to other worlds".
The possibility was ascribed to the notion of "perispirit", considered a semi-material medium, a more subtle body than the physical body allowing the brain's perception, and later considered a synonym of the astral body—an inherent reality explaining apparitions, the materialization of spirits, and the communication through mediums .
Although the theory was completely oversight by its contemporary fellows, the notion permeates more modern references to OBEs in different works from the Brazillian Spiritist movement and their critics . Moreover, while the ability was overshadowed in Spiritism by Mediumship (e.g., practice of channelling), many Spiritist works have exemplified, in many occurrences, the manifestations of the so-called "unfolding" of the astral body, as proposed by Kardec, achieving communication with the spirit worlds and dead relatives during sleep, either spontaneously or through the help of invisible helpers, as exemplified in the following extract from the 1955 book by famous medium Chico Xavier In the realms of Mediumship :
"Clementino [the spirit], in the manner of the common magnetizer, laid his hands on him. Applying a long circuit pass to him [subtle magnetic exteriorization]. Castro [the physical being], felt asleep slowly as if its members became stiff. From his chest, an abundance of whitish steam emanated, which, accumulating like a cloud, quickly transformed, to the left of the dense body, into a duplicate of the medium [incarnated medium, Castro], in a slightly bigger size... The medium, thus disconnected from the carnal vehicle, moved two steps away, revealing the vaporous cord that held it to the somatic field. While the physiological equipment rested, motionless, Castro, fumbling and haunted, emerged, with us [the visiting spirits], in a strange copy of himself, which in addition to being bigger in his external configuration, was blue on the right and orange on the left. In the beginning, his perispirit or "astral body" was clothed with the vital effluvia that ensure the balance between the soul and the body of flesh, known in their whole, as being the "etheric double", formed by neuropsychic emanations that belong to the physiological field and that, therefore, cannot get further away from the terrestrial organization".
Notwithstanding the significant advancements in neuroscience and sleep research in recent years, and despite being a relatively new science, OBEs as non-ordinary states of sleep continue to be shrouded in mystery—more so because of a lack of rigorous testing, replication and validation of any findings in OBE research that could provide insight into such referred realities.
While Kardec's theories of the perispirit, or astral body, have been proposed since the end of the 19th century, much remains to be discovered about the nature of these experiences. As research on Lucid Dreaming and other altered states of sleep consciousness continues to progress, it is possible that we may gain new insights into the nature of the soul (Consciousness) and its relationship to the physical body through careful, scientifically based experimental designs associated with OBEs. Until then, the incredible and often forgotten legacy of Allan Kardec and his work in Spiritism, specifically related to the notion of the unfolding of consciousness in sleep, remains an important reminder of the enduring human quest for understanding the mysteries of life and death. Certainly, the future will see the presented notion as insightful.
Sleep Consciousness Researcher,
Kardec, A. (1860). Le livre des esprits, contenant les principes de la doctrine spirite. Paris, Didier et Cie, Librairies - Éditeurs.
Montenegro, R. (2015). The Out-of-Body Experiences – An Experiential Anthology, Imagens & Letras.
Xavier, Francisco Cândido (1955). Nos Domínios da Mediunidade, Editora FEB (Federação Espírita Brasileira)
 Leading theories of the time.  The The same question was given to different Mediums. The responses were then compared, ascertaining that the messages were coherent between the communication given by Mediums, such as Céline Japhet and the sisters Baudin (at the time 14 and 16 years old), that were blind to the process. Although, it should be noted that Kardec did not refer to the number of Mediums used.  Peri is Latin prefeix meaning “around”. In other others words the perispirit is the manifestation of consciousness or spirit, soul.  The notion was extensively referred to and rationally developed by former Medium and Spiritist Waldo Vieira, who created the movement of Constientiolgy as a dissident of Spiritism.