Pathways to Sleep I: An Introduction
Usually after several hours (for younger people) a remarkable thing happens. We slide (or leap) up to a unique stage that is called REM sleep. This label is attached because it is during this stage that there are rapid eye movements (REMs). These eye movements rarely occur during the other sleep stages—that is why these other stages are given an additional label: NREM (non REM). It is also during the REM stage that dreams often occur. REM sleep is what I was waiting for and was willing to stay up late at night to detect in the lab. When we detected eye movements that were typically accompanied by much more rapid and low volume EEG patterns, we would wait a few minutes and then wake our subject and ask them: “What has been going through your mind.” Typically, there were some vague and often not very colorful dreams to report during this first REM phase. Many times, it wasn’t even clear if the subject was reporting a dream or just night-time ruminations (often wandering randomly through various thoughts).
If we are not sleeping in a dream lab and are not being rudely woken up, then we will soon slip back down to stage four – or more likely to stage three. This third stage, often called gamma sleep, is likely to last for a longer period than the previous delta sleep and is a bit more often found among older adults like myself. We don’t know much about gamma sleep – it is often identified as the “least interesting” sleep stage. But we do know that this stage is just as important as the three more “glamorous” stages. Gamma sleep typically manifests brain waves that are shorter and with lower spikes than delta sleep.
After an hour or two we once again shift to REM sleep and experience more dreams – which are often more colorful and somewhat longer. We only know this is what occurs because we wake people up in a sleep lab when they have been in the REM state for several minutes (or sometimes at least 15-30 minutes). Typically, people do not recall dreams occurring during the middle of the night when they awake in the morning. They only recall these dreams from the middle of the night if the dream has awakened them (for example, a dream that is filled with anxiety) and the dreamer writes something down about the dream. Usually, the dream is not recalled in the morning even if it wakes us up. All we remember is that something disturbing, eventful or (sometimes) joyful occurred during the middle of the night.
Now we are entering the second half of our sleep night. It is common for us to slip back down to NREM sleep after we have been in bed for 3 or 4 hours. At this point, we are most likely to enter Stage Two (beta sleep), which is typified by shorter and even less-extreme peaks in EEG patterns. We also find increases in the Stage One sleep which generates something called “sleep spindles” (bursts in electronic activity). This alpha state is often compared to the state of cortical activity found among people who meditate or engage in other forms of mindfulness.