Fig. 4. Electroencephalographic response to norepinephrine and artificial cerebrospinal fluid infusion into the nucleus basalis of Meynert. (A ) Raw electroencephalogram traces from two rats. In the rat receiving norepinephrine, δ waves are present preinfusion and are reduced postinfusion. In the rat receiving artificial cerebrospinal fluid, δ activity is preserved postinfusion. (B ) Examples of power spectra from a rat after norepinephrine or artificial cerebrospinal fluid infusion, respectively. Note the decrease in low-frequency power in the rat after norepinephrine infusion, and its preservation in the rat after artificial cerebrospinal fluid infusion (arrow ).