Figure 4. Local Sleep Slow Waves.

(A) An example of local sleep slow waves occurring at different times in left and right posterior cingulate cortices, where 100% of units are locked to slow waves. Rows (top to bottom) depict activity in scalp EEG (Cz, red), left posterior cingulate, and right posterior cingulate. Blue, depth EEG; green, MUA; black lines, single-unit spikes. White shadings mark local OFF periods.

(B) Units in concordant “target” regions (expressing the same EEG slow wave, upper panel) exhibit a clear OFF period, while units in non-concordant “target” regions do not exhibit a clear OFF period. Wave-triggered averaging of “target” units is time locked to the positive peak of depth EEG in the “seed” region (blue trace). Red shades denote SEM across neurons (n = 410 in all brain structures).

(C) Most slow waves are local. Distribution of slow wave involvement (percentage of monitored brain structures expressing each wave) is shown.

(D) Global slow waves are of high amplitude. Scatter plot shows slow wave amplitudes as a function of involvement (percentage of brain structures expressing each wave).

(E) A graph depicting the tendency of each pair of regions to express waves concordantly. Nodes (individual regions) are depicted schematically as seen from above, where deep regions away from scalp (MTL) are smaller and scalp electrodes are surrounded by cyan. Node color (legend) denotes the rank of each region—that is, how often it is involved inslow waves seen in other regions. Edge width and color (legend) denotes the probability of each pair of regions to express slow waves concordantly. Note that regions in prefrontal cortex have higher ranks and show concordance across hemispheres relative to MTL.