Pressure myography of posterior cerebral arteries, neurobiology of HF. (a) At baseline, Clock∆19/∆19 PCA have lower myogenic tone versus WT PCA at all transmural pressures >60 mmHg. In the HF mice, and compared to baseline, (b) WT PCA exhibit increased myogenic tone at transmural pressures of 40 mmHg and 60 mmHg, whereas (c) Clock∆19/∆19 PCA have increased myogenic tone at all transmural pressures tested>20mmHg. (d) PCA of all groups respond similarly to phenylephrine, suggesting similar capability to respond. However, as compared to WT PCA, the Clock∆19/∆19 PCA exhibit reduced myogenic tone at baseline, and (e) a greater delta change in myogenic tone in response to HF (e), supporting the notion that the circadian mechanism can influence responses in cerebrovasculature. (f) Summary of the different responses of WT PCA versus Clock∆19/∆19 PCA. All PCA were collected during the middle of the animals’ wake period (Zeitgeber time (ZT19)). *P < 0.05, n = 6 WT PCA, n = 8 WT HF PCA, n = 7 Clock∆19/∆19 PCA, n = 7 Clock∆19/∆19 HF PCA. (g) The circadian mechanism is an important regulator of healthy cognitive system neurobiology. Neurobiological adaptations to HF differ in magnitude and direction in Clock∆19/∆19 versus WT mice, including neuron morphology, visual-spatial memory and cerebrovascular myogenic tone, leading to convergence of end stage measures. These findings highlight the need to better understand how the circadian mechanism affects neurobiological adaptations to HF, a leading cause of morbidity and mortality worldwide. Large black double-sided arrow denotes comparison of normal Clock∆19/∆19 and WT mice. Open white single sided arrows denote comparison of each genotype at baseline and in HF.