Sleep spindles involve activation in the brain in the areas of the thalamus, anterior cingulate and insular cortices, and the superior temporal gyri.
There are slow spindles in the range of 11 – 13 Hz that are associated with increased activity in the superior frontal gyrus, and fast spindles in the range of 13 – 15 Hz that are associated with recruitment of sensorimotor processing cortical regions, as well as recruitment of the mesial frontal cortex and hippocampus.
There is no clear answer as to what these sleep spindles mean, but ongoing research hopes to illuminate their function.
[15][16] Research has also shown that dreams during the NREM stage most commonly occur during the morning hours which is also the time period with the highest occurrence of REM sleep.
It seems that in NREM dreams, the self is put in different situations, largely negative, but is found to respond in a way that befriends or embraces the unfamiliar.
This has two consequences: However, because the diaphragm is largely driven by the autonomous system, it is relatively spared of non-REM inhibition.
This problem is exacerbated in overweight people when sleeping on the back, as extra fat tissue may weigh down on the airway, closing it.
The brain activity during sleep, according to this study, would show the events of the previous day do make a difference.
This process of reactivation of memory firing sequences is believed to gradually reinforce initially weak connections between neocortical sites allowing the original information to be activated in the cortex independently of the hippocampus, and thus ensuring refreshed encoding capacity of the hippocampus."
[21] NREM SWS, also known as slow wave activity (SWA), is regarded as highly important in brain development due not only to its homeostatic behavior but also because of its distinct correlation with age.
[23] An increase in SWA peaks just before puberty and exponentially decreases from adolescence to adulthood in both longitudinal and cross-sectional studies of typically developing participants.
[24][22][23][25] This phenomenon is understood as memories and learned skills being metabolized during NREM sleep;[22] the decrease in SWA is considered a reflection of synaptic rewiring and, therefore, an effect of behavioral maturation concluding.
For example, children with attention deficit hyperactivity disorder (ADHD), a brain disorder that affects cognitive and motor control, have shown considerably different cortical thickening trajectories in contrast with typically developing children per MRI data.
[28] NREM sleep has been demonstrated to be intimately correlated with declarative memory consolidation in various studies, where subject slept after a declarative memory-task; these who had a sleep imbued of NREM stages, had a better performance after the nap or the night, compared to subjects who have been awake or had more REM-sleep.
[32][33] Furthermore, the specific and crucial role of SWS (Slow-Wave Sleep, a stage of NREM sleep) in memory consolidation has been demonstrated in a study[35] where, through electrical stimulations, slow oscillations were induced and boosted; because of this SWA increase, participants had a better performance in declarative memory tasks.
Not only SWA helps learning, but it is also crucial, because its suppression has been demonstrated to impair declarative memory consolidation.
Theta waves interacts with gamma activity, and - during NREM - this oscillatory theta-gamma produces the relocation of the memory representation, from the hippocampus to the cortex.
On the other hand, sleep spindles increase occurs right after or in parallel to the theta augmentation, and is a necessary mechanism for the stabilization, the reinforcement and also the integration of the newly encoded memory trace.
[34] Importantly, in this working model, slow oscillations have the role of a 'time-giving pace maker',[34] and seem to be a prerequisite for the success of cueing.
According to this model, enhancing only slow waves or only spindles, is not sufficient to improve memory function of sleep: both need to be increased to obtain an influence and this latter.
[34] Not much is known about NREM, so scientists have conducted studies in other animals to potentially understand more, in particular why the brain has evolved to have two distinct states.