Sleep is a universal drive in most animals, and an active focus in neuroscience over the past decades. Many mechanisms involved in sleep regulation and the critical role sleep plays in cognition, immunity and overall health have been deciphered, while many remain to be uncovered. From an evolutionary point of view, it would seem that conscious rest would have been less dangerous, since the brain could react to threats, yet unconscious sleep offered advantages for the brain we are only now beginning to understand.
We know that during sleep the immune system is removing waste and fighting infections by activating a type of cell in the brain called microglia, and we also know that learning and memories are consolidated during sleep. Acute sleep deprivation can lead to psychological changes and when severe, to impaired memory, mood changes, psychosis, or seizures. Many neuropsychiatric disorders display sleep dysregulation as part of their spectrum of symptoms.
In the process of neurofeedback training, especially in the beginning, sleep is an important factor we monitor. Often an active changing of habits is needed in order to support the learning occurring during the neurofeedback session. But why is sleep important for learning and how does sleep support it?
Sleep is composed of a series of states that differ in in their patterns of electrical and chemical activity, which together are called sleep architecture. Upon falling asleep, the brain starts in what is known as slow-wave sleep (SWS), where low frequency oscillations are prevalent, and then the pattern switches to a period of rapid eye movement (REM) sleep, which appears from the point of view of brain wave (EEG recordings) almost indistinguishable from the awake state and is characterized by fast oscillations. Dreams can occur in both REM and SWS states, with different characteristics. These cycles repeat throughout the night in a predictable pattern in healthy individuals. Sleep begins with shallow SWS, progresses to deeper SWS (during which it is difficult to awaken the individual), returns to light SWS, and then switches to REM sleep before starting a new cycle. Neurotransmitter (intrinsic brain chemicals) production is also specific to these phases, with a decrease in serotonin and acetylcholine during SWS and return of waking-level acetylcholine during REM.
REM and SWS play separate roles in memory but during both stages there are two fundamental processes that are considered key to neuroplasticity, which is the property of the brain to remain changeable and learn. On one hand, connection between the cells of the brain (called neurons) are actively built during sleep, while the brain reruns various sequences in the same regions as they occurred during waking, or modifies and moves them in various other areas. Paradoxically, the brain is thus not less active during sleep than when engaged in daily activities, it simply switches to an active maintenance mode. In this respect, to sleep is to remember.
The second process occurring during sleep is a removal of unwanted connections made during the day. To sleep is also to forget, but the brain does that selectively. As more and more associations are made during the day, the brain is running the risk of becoming less functional. Sleep scales back these connections called synapses to prevent overload and thus optimizes and prepares for the next cycle of awake functioning. Some connections are lost selectively while other sequences (memories) are stored, changed and reshaped. Motor sequence memories, such as learned rhythms, are replayed, abstracted and even enhanced, including those that are imagination-based. This supports the idea that new skills can be strengthened by sleep, which is performing an active and even creative role. It is a common experience to wake up after a good night sleep and “come up” with fresh creative ideas. They do not come from a vacuum though; they are the result of the brain processing existing information and creating new connections.
The emotional component of human perception also plays a role in learning or memory, similar to a gain factor. It has been shown that sleep can boost and improve learning if the person feels an emotional reward connected with the content of the learned subject. For optimal efficiency, one must enjoy learning…and then sleep on it.
Overall, sleep prepares the brain to be able to properly acquire, select, and store information. A balanced waking state of perception, learning, and motor control during the day are optimized as long as sleep can clean and selectively reorganize the system during the night.
Sleep on it!
