Sometimes a pathology can provide a unique possibility of studying brain functioning. It is the case of Narcolepsy with cataplexy - Type 1 Narcolepsy - a debilitating condition caused by the reduction of hypocretin-1, an important neurotransmitter in the regulation of the sleep-wake rhythm, as well as of the neurons that release it.

The possibility to study the neural bases of the dream in patients suffering from excessive daytime sleepiness has allowed the team of researchers of the Department of Psychology of Sapienza and the University of Bologna, together with researchers from the University of L'Aquila and the IRCCS Institute of Neurological Sciences of Bologna, to unveil the mysterious mechanism of the dreamlike experience. The results of the study have been published in the journal Annals of Clinical and Translational Neurology.

"The peculiarities of the sleep quality of patients with narcolepsy - explains Luigi De Gennaro from Sapienza University - have made it possible to clarify that the dream experience is not limited to the REM stage only, but shows characteristics that largely overlap also the Non-REM stages of sleep ". On a sample of 238 patients recruited at the Department of Biomedical and Neuromotor Sciences of the University of Bologna, the researchers selected 43 diagnosed with type 1 narcolepsy, that underwent the Multiple Sleep Latency Test (MSLT), the standard clinical test for the assessment of excessive daytime sleepiness.

Once awaken from the 5 naps scheduled during the day, the presence of dreams was assessed and was related to the brain electrical activity of the minutes before awakening. "In this way - continues De Gennaro - we could observe not only how the repeated sleep attacks are characterized by a rich dreamlike experience, but also by a beginning  in REM sleep stage".

From this discovery derived another important acquisition. At the base of  dream recall there is a single physiological mechanism, the electrophysiological activation level. In other words it is easier to remember dreams in the presence of a higher activation of the cerebral cortex. The study also confirmed that a network of posterior brain areas is the basis of the dream experience.

"It all started many years ago - explains De Gennaro - when we started the systematic study of the neural bases of dreams. The initial idea was that the brain mechanisms of the dream could be overlapping with the mechanisms underlying the re-enactment of episodic memories during the day. Despite the different results obtained in recent years, up to now the uniqueness of the dream experience in the REM phase still remained an unsolved question".

The discovery has implications that open up potentially innovative perspectives for the identification of dream mechanisms, which come from the study of some specific sleep disorders, called parasomnias. The team of authors of the study is conducting a wide project on pathologies such as the somniloquy, which could allow direct access to the dreamlike experience. The next goal is to clarify how a linguistic expression during the sleeping activity underlies mechanisms similar to linguistic programming during wakefulness.

References:

Cortical activation during sleep predicts dream experience in narcolepsy - Aurora D'Atri, Serena Scarpelli, Cinzia Schiappa, Fabio Pizza, Stefano Vandi, Michele Ferrara, Carlo Cipolli, Giuseppe Plazzi, Luigi De Gennaro - Annals of Clinical and Translational Neurology 01 February 2019| https://doi.org/10.1002/acn3.718

Further information

Luigi De Gennaro
Department of Psychology  - Sapienza University of Rome
luigi.degennaro@uniroma1.it