CA4 and obstructive sleep apnea syndrome: The High OSA group had a significantly greater area fraction than the Low OSA group in both the fimbria (1.33-fold; 2.85 ± 0.26 vs. 2.14 ± 0.14, t (20) = 2.401, p = 0.026) and the CA4 (1.24-fold; 6.12 ± 0.38 vs. 4.95 ± 0.22, t (22) = 2.649, p = 0.015).