![]() Īlthough the function of sleep spindles is unclear, it is believed that they actively participate in the consolidation of overnight declarative memory through the reconsolidation process. The time scale at which the waves travel at is the same speed it takes for neurons to communicate with each other. It has been suggested that this spindle organization allows for neurons to communicate across cortices. It was determined that oscillations sweep across the neocortex in circular patterns around the neocortex, peaking in one area, and then a few milliseconds later in an adjacent area. Until recently, it was believed that each sleep spindle oscillation peaked at the same time throughout the neocortex. Research supports that spindles (sometimes referred to as "sigma bands" or "sigma waves") play an essential role in both sensory processing and long term memory consolidation. Only in humans, rats and dogs is a difference in the intrinsic frequency of frontal and posterior spindles confirmed, however (spindles recorded over the posterior part of the scalp are of higher frequency, on average above 13 Hz). Considering animals in which sleep-spindles were studied extensively (and thus excluding results mislead by pseudo-spindles ), they appear to have a conserved (across species) main frequency of roughly 9-16 Hz. Sleep spindles have been reported (at face value) for all tested mammalian species. After generation as an interaction of the TRN neurons and thalamocortical cells, spindles are sustained and relayed to the cortex by thalamo-thalamic and thalamo-cortical feedback loops regulated by both GABAergic and NMDA-receptor mediated glutamatergic neurotransmission. Sleep spindles are bursts of neural oscillatory activity that are generated by interplay of the thalamic reticular nucleus (TRN) and other thalamic nuclei during stage 2 NREM sleep in a frequency range of ~11 to 16 Hz (usually 12–14 Hz) with a duration of 0.5 seconds or greater (usually 0.5–1.5 seconds). For other uses, see Spindle (disambiguation).
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