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Your brain cycles through different stages of sleep several times a night, which determine the quality of your sleep. After an initial five to ten minutes in stage one sleep, your brain moves into a deeper stage two, and over the next hour it goes to stages three and four in which the electrical activity slows way down. Hence, these periods are called slow-wave sleep. After slow-wave sleep, your brain progresses into REM (rapid eye movement) sleep, in which it becomes a lot more active.
Studies have shown that people with depression experience more REM sleep and spend less time in slow-wave sleep, which means their sleep is not as restful. In fact, one of the ways antidepressant medications help is that they reduce REM sleep. Your brain runs through the sleep cycles sequentially about every hour and a half and then starts over again at the beginning. So, if you don’t sleep contiguously and you don’t get to go through the entire cycle, your slumber is less restorative to your brain. The quality of your sleep suffers, which you’ll feel even though the number of hours slept may be adequate.
Interestingly, if you wake up in cycle one, you feel more rested than if you come out of one of the other stages. You can actually purchase alarm clocks and applications that monitor your brain waves and wake you up in stage one. However if you wake up at the same time every day, your brain naturally rouses you in stage one.
Depression and sleep problems go hand-in-hand. While many factors contribute to this, a big one has to do with the communication between the brain’s prefrontal cortex and limbic system during sleep. Fundamentally, depression is a malfunction in a brain’s frontal-limbic communication system of which the hippocampus is an essential part. Alex Korb, in The Upward Spiral: Using Neuroscience to Reverse The Course of Depression, One small Change at a Time explains it this way:
During sleep, the hippocampus talks to the prefrontal cortex by sending bursts of communication that the prefrontal cortex responds to. Thus sleep is important for proper frontal-limbic communication, which is why disrupting your sleep can be so harmful, and why improving your sleep is such a great way to start an upward spiral.
