Red-eye flights, all-night study sessions, and extra-inning playoff games all deprive us of sleep and can leave us forgetful the next day. Now scientists have discovered that lost sleep disrupts a specific molecule in the brain's memory circuitry, possibly leading to treatments for tired brains. Neuroscientists studying rodents and humans have found that sleep deprivation interrupts the storage of episodic memories: information about who, what, when, and where. To lay down these memories, neurons in our brains form new connections with other neurons or strengthen old ones. This rewiring process, which occurs over a period of hours, requires a rat's nest of intertwined molecular pathways within neurons that turn genes on and off and fine-tune how proteins behave.
Neuroscientist Ted Abel of the University of Pennsylvania and colleagues wanted to untangle these molecular circuits and pinpoint which one sleep deprivation disrupts. The researchers started by studying electrical signals in slices of the hippocampus–the brain's memory center–from sleep-deprived mice. They tested for long-term potentiation (LTP), a strengthening of connections between neurons that neuroscientists think underlies memory. When the scientists tried to trigger LTP in these brain slices with electrical stimulation or chemicals, they found that methods that fired up cellular pathways involving the molecule cyclic adenosine monophosphate (cAMP) didn't work. Brain cells from sleep-deprived mice also held about 50% less cAMP than did cells from well-rested mice. In the brain, cAMP acts as a molecular messenger, passing signals between proteins that regulate activity of genes responsible for memory formation.