![]() ![]() Though some fMRI/PET studies have investigated functional connectivity associated with REMS 13, 14, the limited temporal resolution and complexity of these techniques impedes the characterization of whole-brain networks during single REMS episodes. Apart from the hippocampal structure 10, 11, 12, electrophysiological data during REMS remains sparse. Taken together, these examples show that REMS is a complex brain state which involves many brain regions scattered across the brain, rendering the global investigation of REMS challenging. However, the downstream activations of these pathways are completely unknown. Furthermore, the melanin concentrating hormone, known to play a role in the promotion of REMS, is synthesized by neurons in the hypothalamus 9. ![]() For example, in the brainstem 8, two subsets of glutamatergic neurons (so called REM-on neurons) located in the latero-dorsal tegmental area and in the sub-latero-dorsal tegmental nucleus have been described: the first one projecting to the forebrain, responsible for the generation of hippocampal theta rhythm and desynchronized cortical activity, the second one projecting to the brainstem and responsible for muscle atonia hence the suppression of motor activity 2. ![]() However, to build a unified understanding of this complex state, a clear global picture of brain activity during spontaneous REM sleep is critical, but currently missing.įrom a physiological point of view, complex brain circuits have been shown to play a role in REMS. Over the past decade, sleep researchers have accumulated evidence showing that REM sleep is a complex state produced by anatomically distributed neural circuits, serving a wide variety of functions critical for emotional regulation, memory and development 5, 6, 7. Moreover, the discovery of REMS has triggered a paradigm shift in considering sleep as a state during which critical operations are performed despite apparent behavioral quiescence 3, 4. This last observation strongly challenges the view of sleep as a passive state. Though the first one is characterized by quiescent brain activity and low-energy expenditure, the second is actually associated with ‘activated’ brain state, phasic muscular activation despite body paralysis and increased energy consumption and metabolic load 2. Interestingly, most species, encompassing insects, fishes, birds and mammals exhibit two types of sleep: non-REM sleep and REM-sleep (REMS) 1. Sleep is ubiquitous in animals, yet its functions remain unknown. This last finding suggests that the amygdala undergoes specific processing during REMS and may be linked to the regulation of emotions and the creation of dream content during this very state. Finally, we report a peculiar activation pattern in the posterior amygdala, which is strikingly disconnected from the rest of the brain during most REMS episodes. Second, we isolated the vascular compartment in our recordings and identified arteries in the anterior part of the brain as strongly involved in the blood supply during REMS episodes. ![]() We first demonstrate a dissociation between basal/midbrain and cortical structures, the first ones sustaining tonic activation during REMS while the others are activated in phasic bouts. In the present work, we performed functional ultrasound imaging on rats over multiple coronal and sagittal brain sections during hundreds of spontaneous REMS episodes to provide the spatiotemporal dynamics of vascular activity in 259 brain regions spanning more than 2/3 of the total brain volume. The mechanisms and functions of these energy-demanding patterns remain elusive and a global picture of brain activation during REMS is currently missing. Rapid-eye-movement sleep (REMS) or paradoxical sleep is associated with intense neuronal activity, fluctuations in autonomic control, body paralysis and brain-wide hyperemia. ![]()
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