system
Given the following post, respond as if you're commenting on Reddit:
human
What happens in the brain in the moments following the transition between trying to fall asleep and actually sleeping?
gpt
Sleep physiology is pretty complex. Sleep itself is divided into 2 types (NREM and REM) and 4 different stages. NREM, or non-REM is divided into stage 1, stage 2, and stage 3 (formerly 3 and 4). While REM, or rapid eye movement is its own stage with different physiology. When awake, a person has a characteristic brain wave pattern as recorded on EEG. This type of wave is called alpha wave activity. As we lie down to go to sleep we go into stage 1 of sleep, the brain wave activity changes to beta waves. Stage 2 of sleep is reached when the EEG recording detects k-complexes and/or sleep spindles. Stage 3 of sleep is the deepest sleep, characterized by delta waves. Normal physiologic secretion of growth hormone occurs during stage 3 sleep, which is why sleep is actually really important for growth (mom was right!). Following stage 3, a person can enter into a period of REM sleep. REM sleep is probably the strangest phase of sleep, and is the most studied. We know that dreaming occurs during REM, as well as near-complete paralysis of the body. Most sleep-related breathing disorders and behavior disorders occur during REM. Each REM-cycle, from stage 1/2 to 3 to REM, takes about 90 minutes to complete. The duration of REM increases with each REM cycle throughout the night. The best stage to be woken from is stage 1 or 2, while being woken from stage 3 or REM can leave you groggy for up to 30-45 minutes.

&#x200B;

To answer your question a bit more precisely, when awake and alpha waves are present, the brain activity signals an active cortext, and the EEG is unsynchronized and rapid. Beta waves indicate a lowered level of alertness, and the waves are slower and synchronized. Theta waves indicate activity in the hippocampus, meaning likely memory formation or storage. Delta waves indicate that neurons are not engaged in processing information and across the brain are firing together, giving large, synchronized waves in the EEG tracing.