FIGURE 3.

A sketch of the sequence of key accommodation-related events during sleep. As one moves from awake state into light sleep (NREM1) the frontal lobe is actively inhibited (increase in delta band spectral power) while the posterior areas the spectral power is reduced in the alpha and higher frequency bands, entirely consistent with signal changes along the anterior posterior midline in the EEG (De Gennaro et al., 2001) and MEG (Ioannides et al., 2009, 2017). This general trend continues and intensifies during NREM2, except for focal increases in the alpha and low sigma bands in a few foci in the frontal pole, and specifically in the rACC (Ioannides et al., 2017). These changes reveal an element of environmental monitoring has returned amidst the general loss of executive function. From this point on a bifurcation takes place, with one scenario pushing toward spindles and the other toward KCs. In both scenarios, i.e., for both spindles and KCs, only increases in activity are encountered. In the comparison between the 2 s period before spindles with the core period of NREM2 only focal increases low frequency spectral power are encountered (mainly in the delta band) in the frontal lobe. The rACC is one of the few areas inhibited in this way before spindles. During spindles focal increases in spectral power are identified, in the alpha and low sigma bands in the areas adjacent to the MSRC main nodes and in orbital frontal cortex (OFC, BA11) and basal forebrain, in the anterior region of nucleus basalis of Meynert (NBM). Before and during KCs widespread increases are encountered in the delta, theta, and alpha band in the frontal lobes. These increases suggesting a struggle between inhibition and excitation in the frontal lobes. In the 2 s before KCs there is no inhibition of rACC (no spectral power increase in the delta band), as it was seen in the pre-spindle period, suggesting that the return of environmental monitoring seen in the NREM2 core period is maintained. Significantly, during KCs increases are identified in large areas of frontal lobes, including rACC in the delta band and in higher frequencies, consistent with intensification of the struggle between inhibition and excitation of frontal lobe executive function. For spindles, the chain of events seems to lead to a main process that requires cooperative activity between the ventral structures and basal forebrain, as well as activity in the sigma band which links the DMPFC (MSRC1) and the posterior parietal areas (MSRC2). The process of accommodation continues in deep sleep with trimming of connections and further processing during REM tonic phase (Andrillon et al., 2017) and possibly the running of likely extreme scenarios in the newly defined ZPD, making dreams a kind of play preparing for the following day’s struggles.