Fig. 4.

The effect of severe bilateral (>80%) lesions of the VLPO cluster on delta power and NREM sleep. A, Comparison of delta power in the EEG plotted over 24 hr for a single animal with >90% cell loss in the VLPO cluster bilaterally (R1352) before lesion (gray) and 6 d after lesion (black) is shown. The blackbaralong the bottom of the graph indicates the dark cycle. Note the nearly complete loss of periods of greatest delta activity during the first part of the sleep cycle (just after lights on) and during the brief episodes of sleep during the dark cycle. B, For the entire group of seven rats with severe bilateral VLPO lesions, there was loss of nearly 55% of NREM sleep time. In particular, NREM sleep bouts during the dark cycle were almost entirely eliminated. However, circadian variation in NREM sleep time persisted. *p < 0.05; **p < 0.01.