Figure 3.

A typical REM sleep-like episode elicited by carbachol injection into the dorsomedial pontine tegmentum while recording extracellularly from a noradrenergic cell of the LC. Characteristic of these episodes are reduction of low-frequency components in favor of higher frequencies (6–12 Hz) in the power spectrum of cortical electroencephalogram (EEG), the appearance of theta-like rhythm in the hippocampus (HIPP; 3–4 Hz under anesthesia; Vertes et al., 1993; c.f., graphs at the bottom), reduction of inspiratory activity of the hypoglossal (XII) nerve, and slowing of the respiratory rate. The top two traces show that, when these changes occur, noradrenergic LC cells stop firing. The episodes typically last 2–4 min. The record was obtained in a related study (Fenik et al., 1999). XII nerve trace shows integrated activity of the XII nerve, with each upward deflection corresponding to the inspiratory phase of the central respiratory cycle. The power spectra were calculated for a 60-s period of activity prior to carbachol injection (open circles) and for a 60-s interval centered on the peak of the response to carbachol (filled circles). Arrows point to the parts of the spectra where differences can be noted between the control period and the period of REM sleep-like episode.