By Roxanne Lee
Researchers reported on April 29 that it is changes in ion concentrations, and not nerve cell activity, that switch the brain between its waking and sleeping states.
The study, conducted by Ding et al., focused on the collection of ions and residue in cerebrospinal fluid (CSF). CSF flows in the ventricles and around the surface of the brain and spinal cord. CSF’s primary purpose is to cushion the brain and act as a shock absorber; it also circulates nutrients and chemicals from the blood and removes waste from the brain.
Previously, scientists assumed that neurons drove the changes between sleep and wakefulness. In fact, it took this long to discover the link between ions and our sleep wake cycle because they were so focused on neurons.
The lead author of the study, Maiken Nedergaard, co-director of the University of Rochester Center for Translational Neuromedicine, said, “We found that the transition from wakefulness to sleep is accompanied by a marked and sustained change in the concentration of key extracellular ions and the volume of the extracellular space.”
Nedergaard and her team discovered that the fluid between brain cells changed in predictable patterns in their experiments on mice; potassium levels were high when the mice were awake, and dropped during sleep, and calcium and magnesium ions behaved in the opposite manner. These ion levels in the brain are controlled by neuromodulators, brain chemicals which affect the brain by bypassing nerve cells and changing ion concentrations.
The study recorded similar changes when observing ion levels in animals put under anesthesia. When anesthetized mice were given a chemical cocktail of neuromodulators, their potassium levels rose to wakefulness levels, and the mice woke up in seconds, but their levels of calcium and magnesium took longer to drop. The mice exhibited great confusion, acting groggy and bumping into the walls of their cages. This may explain why people recently woken up from anesthesia are immediately disoriented before they fully wake up.
These findings may help pave the way to discover the exact mechanism by which the brain activates billions of nerve cells simultaneously when the brain wakes up. Hopefully this will lead us to a greater understanding of sleep, consciousness, and sleep disorders as well.