Studying mice, scientists at Johns Hopkins have fortified evidence that a key purpose of sleep is to recalibrate the brain cells responsible for learning and memory so the animals can "solidify" lessons learned and use them when they awaken -- in the case of nocturnal mice, the next evening.
The researchers, all of the Johns Hopkins University School of Medicine, also report they have discovered several important molecules that govern the recalibration process, as well as evidence that sleep deprivation, sleep disorders and sleeping pills can interfere with the process.
"Our findings solidly advance the idea that the mouse and presumably the human brain can only store so much information before it needs to recalibrate," says Graham Diering, Ph.D., the postdoctoral fellow who led the study. "Without sleep and the recalibration that goes on during sleep, memories are in danger of being lost." A summary of their study appears online in the journal Science on Feb. 3.
Diering explains that current scientific understanding of learning suggests that information is "contained" in synapses, the connections among neurons through which they communicate. On the "sending side" of a synapse, signaling molecules called neurotransmitters are released by a brain cell as it "fires"; on the "receiving side," those molecules are captured by receptor proteins, which pass the "message" along.
If a cell receives enough input through its synapses, it fires off its own neurotransmitters. More specifically, experiments in animals have shown that the synapses on the receiving neuron can be toggled by adding or removing receptor proteins, thereby strengthening or weakening them and allowing the receiving neuron to receive more or less input from nearby signaling neurons.