In this video, I will draw the EEG waveforms of our patient, Bob, going through the different stages of sleep going chronologically from waking life to deep sleep to dreaming.
First, Bob starts the process of going to bed by brushing his teeth. Right now, his eyes are open and he has active mental concentration on his task. His brain is busy, which is reflected by the beta waves of the EEG waveform. Beta waves have the highest frequency (14 – 30 Hz) and the lowest amplitude which represent the organized chaos inside a busy brain.
Next, Bob lies down to sleep. He closes his eyes and his brain transitions into the alpha wave pattern. No longer processing visual information, the brain slows down which is reflected by the 9 – 13 Hz alpha waves.
Now, Bob has fallen asleep and enters into stage 1 of non-REM sleep. This state of reduced consciousness shows on the EEG as slower theta waves (4 – 8 Hz) and can also be found when undergoing deep meditation. This stage of sleep is only 5% of the total sleep time for adults, and so Bob quickly enters into stage 2 of non-REM. This stage looks similar to stage 1, but is characterized by sleep spindles and K complexes. Sleep spindles are bursts of rapid, rhythmic activity, and K complexes are brief large spikes of activity. Sleep talking and teeth grinding happen in this stage which is also the plurality of sleep time at 45% of the total.
Next, Bob enters stage 3 of non-REM, about 25% of total sleep time. This stage is reflected on the EEG as Delta waves which have the lowest frequency (below 4 Hz) and the highest amplitude. This is the deepest stage of sleep where Bob loses all bodily awareness. Unfortunately for some patients, this is also when sleep walking, night terrors, and bed wetting can occur.
Finally, Bob completes a sleep cycle by entering into the most fun stage of sleep – Rapid Eye Movement, or REM sleep. This stage has sawtooth-like, low voltage, high frequency waves that most closely resemble beta waves. There is a loss of motor tone throughout the body except in the extra-ocular eye muscles hence the “rapid eye movements.” This stage is when vivid dreaming occurs, usually lost to memory upon waking. It is thought that REM sleep also facilitates memory processing, to reinforce long-term memories.
Two things to take away from this video. First, notice how the higher frequency waves correspond with more intense brain activity. Second, know how to draw the 6 EEG waveforms in order by using the mnemonic “At night, BATS Drink Blood”
This concludes our video on Bob’s first sleep cycle. Be sure to like and subscribe for more videos!