New experiments reveal the mysteries of sleep depth and duration

There are many theories on why humans even need to sleep, but I’m pretty sure it’s to charge our phones. —@alispagnola

Sleep, as a science, is being dissected and scrutinized with increasing intensity. Both society in general, and the medical community, have growing appreciation for both the vital role of sleep in physical, mental, emotional, and spiritual wellbeing, and for the powerful, pervasive, consequences of insufficient sleep.

Although the body of knowledge about sleep is growing rapidly, how much we need to sleep, and what controls depths of sleep, still elude understanding. A new study at the University of Tsukuba, Japan, provided some answers. The scientists discovered a signaling pathway within brain cells that regulates depth and duration of sleep.

“We examined genetic mutations in mice and how these affect their patterns of sleep,” says senior author of the study, Professor Hiromasa Funato, in a statement. “We identified a mutation that led to the mice sleeping much longer and more deeply than usual.” The researchers found that this was caused by low levels of an enzyme called histone deacetylase 4 (HDAC4), which is known to suppress the expression of target genes.

They also identified another protein, LKB1, which has similar sleep-suppressing effects when deficient.

“Our findings indicate that there is a signaling pathway within brain cells which promotes sleep, probably because it affects the expression of sleep-promoting genes,” says study co-senior author, Professor Masashi Yanagisawa. “This pathway phosphorylation of HDAC4 promotes sleep, probably because it affects the expression of sleep-promoting genes.”

The team performed additional experiments to identify the brain cells in which these pathways regulate sleep. This involved altering the amounts of SIK3 and HDAC4 in different cell types and brain regions. The results indicated that signaling within the cells of the cortex regulates the depth of sleep, while signaling within the hypothalamus regulates the amount of deep sleep. For both brain regions, the excitatory neurons, which can activate other neurons, were identified as playing a key role.

The study was published in Nature.

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About the Author

Dr. Faith Coleman

Faith A. Coleman MD
Dr. Coleman is a graduate of the University of New Mexico School of Medicine and holds a BA in journalism from UNM. She completed her family practice residency at Wm. Beaumont Hospital, Troy and Royal Oak, MI, consistently ranked among the United States Top 100 Hospitals by US News and World Report. Dr. Coleman writes on health, medicine, family, and parenting for online information services and educational materials for health care providers.

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