Who discovered rapid eye movement sleep? The claims for precedence

Controversies over who deserves academic credit for pioneering scientific discoveries are probably as old as scientific research itself. The relatively young field of sleep research is no exception. Who should be credited for the discovery of rapid eye movement (REM) sleep?

The 1953 discovery published in Science by Aserinsky and Kleitman [1], is unanimously agreed upon as the “launching pad” of sleep research as a field of scientific investigation. Should the credit go to Eugene Aserinsky, the student, or to Nathaniel Kleitman, the professor, who at the time of the discovery was already a world-renowned sleep researcher, the first to dedicate his entire academic activity to sleep? Recently, new candidates have been competing for credit.

In a special article [2], Kristina Denisova provided an English translation of a 1926 paper by Maria Denisova and Nicolai Figurin, investigators from The Infant Division at the Institute for Brain Research in Leningrad, titled Periodic Phenomena in The Sleep of Children. According to Denisova, "it is the first study to report data on what is currently termed rapid eye movement (REM) sleep.” Michael H. Silber [3] published a detailed response to Denisova’s claim arguing that “partial identification of a phenomenon is insufficient to get full credit for a scientific discovery,” and that therefore, the discovery should not be credited to Denisova and Figurin.

He bases this argument on the specific developmental period (infancy) of the phenomenon, the mode of measurements (i.e. prior to the identification of EEG and EOG), the lack of identification of an association with dreaming, the limited understanding of underlying mechanisms, and the absence of further research. In her response to Silber, Denisova [4] delineates the relevant criteria for establishing novel phenomena in empirical investigation, arguing that these criteria were met in the 1926 study. She goes on to specifically rebut each of the claims raised by Silber in regard to “partial identification of a phenomenon.” We would like to approach this controversy from yet another perspective.

The fact that the 1926 and 1953 papers addressed different questions, and therefore focused on different phenomena, is central and relevant to the question of precedence. Denisova and Figurin investigated breathing in sleeping infants, while Aserinsky and Kleitman aimed to investigate the oculomotor performance during the transition from wakefulness to sleep and in sleep. Thus, although the Denisova and Figurin study from 1926 described eye movements in infants appearing concomitantly with rapid and unstable breathing in sleep, findings that are undoubtedly in accordance with Aserinsky and Kleitman’s observations reported in 1953 in adults (and later in infants in 1955), the appearance of eye movements was not the focus of their study.

This is evident first from their lengthy descriptions of the breathing curves of infants in the second period (starting in the last paragraph on page 7 to the middle of page 9), only after which they describe: “During the periods of increased rapidity of breathing, there is a concentration of movements, both general as well as local, and definitely the movements of eyelids.” Indeed, when discussing possible underlying mechanisms, they viewed eye movements as a secondary phenomenon, resulting from the breathing cycle: “One needs to recall” they wrote, “that the reticular formation (in which so-called breathing centers are located) is linked via the dorsal longitudinal fasciculus with the centers of eye movement muscles, as well as linked with nucleus n. facialis.” Moreover, after ruling out several “endogenous” and “exogeneous” potential causes of the periodicity in breathing, such as changes in body position, time of day, light, urination, and noise, Denisova and Figurin hypothesized that the breathing cycle and its motor components reflect “insufficient coordination of the work of the sympathetic and parasympathetic systems.” Finally, Denisova’s claim [4] that “Denisova and Figurin recognized the importance and novelty of their finding” raises a flag of ambiguity. It is noteworthy that they hypothesized that the periodic cycles were characteristics of a transient developmental period in infants aged 1–2 months to 2 years that disappeared after 2 years when the two systems “become mutually balanced.” Indeed, in the first paragraph of their introduction, they set the stage by stating: “A child, especially a newborn, is strikingly different from an adult, and not only morphologically, but also with respect to functional particularities . . . of the various systems of inner organs.” Consistent with this view, and as periodic phenomena were not identified in their study of sleep in four adults, they state that: “. . . only in the third period, after second year of life, sleep with predominance of rest is established.” This suggests not only that the phenomenon was recognized only in infants (as noted by Silber), but that their frame of reference was based on the prevailing notion of their time, that the function of sleep in adults (here specifically in breathing and motility) is to achieve the state of rest. It is clear that they did not view their findings as a breakthrough or a paradigm shift.

Did Denisova and Figurin’s study influence future sleep research? Did their findings influence Kleitman’s research? Written in Russian and published in a local journal it is unlikely that the paper was available to people who had an interest in sleep or in biological rhythms.

It is not surprising, however, that Kleitman, who was born in Kishinev and therefore spoke Russian, cited the paper in the first edition of Sleep and Wakefulness [5], (pages 80, 126, and 487). He cited the paper in the chapters on respiration in sleep, on motility in sleep, and on humoral theories of sleep, where he provided the authors’ hypothesis that the cycles originated from the imbalance between the sympathetic and parasympathetic systems. The paper is cited seven times in the 1963 edition of the book [6] (pages 50, 52, 88, 91, 112, 357, and 364).

It is obvious from the way Kleitman described Denisova and Figurin’s findings, that he did not consider the motor components of the breathing cycle of major importance. In fact, he saw them as accessory phenomena to the breathing cycle. Yet he did not ignore these findings.

In the final chapter of the book entitled “The Evolutionary Theory of Sleep and Wakefulness” in which he developed the basic rest-activity cycle (BRAC) concept, which appears in advanced sleep as a series of dreaming episodes and in advanced wakefulness in recurrent fluctuations in alertness, he suggested that the breathing and motor cycles observed first by Denisova and Figurin, and then later [7] in his own laboratory, as the early manifestation of the basic rest-activity cycleBRAC. This concept was central to Kleitman’s theory about sleep and the REM-non-REM cycle [8]. Taken together, we agree with Silber that Denisova and Figurin’s observations of REMs appearing in tandem with rapid and unstable breathing in a study aiming to investigate breathing patterns in infants’ sleep cannot be accepted as proof of discovery precedence, nor as a paradigm shift.

The claim for precedence in discovering REM sleep by Denisova and Figurin could be justified if Kleitman and Aserinsky had begun investigating eye movements in sleep after reading their paper, but this was obviously not the case. Therefore, the credit for the discovery of REM sleep should remain with the Chicago team of the student and his professor. Financial disclosure: Authors have no financial disclosures.

Nonfinancial disclosure: Authors have no conflicts of interest.