Fig. 6. Cross-approximate entropy (C-ApEn) before and after pharmacologic manipulation of the nucleus basalis of Meynert. (A ) C-ApEn remained steady preinfusion (red circles ) and increased after norepinephrine infusion (blue circles ). (B ) Box plot of the mean C-ApEn preinfusion and postinfusion with norepinephrine (n = 11). (C ) C-ApEn remained steady preinfusion (red circles ) and did not change after artificial cerebrospinal fluid infusion (blue circles ). (D ) Box plot of the mean C-ApEn preinfusion and postinfusion with artificial cerebrospinal fluid (n = 10). *P < 0.01 versus zero. Error bars are ± 1 SD; n = number of rats.