IL6 and mood disorder: The majority of studies examining the relationship between parasympathetic/vagal activity and systemic inflammation use resting heart rate variability (HRV) measurements.20,21,40,41 However, resting HRV is associated with the activity of prefrontal-amygdala pathways42and is decreased in stress-related mood disorders.43 Our own lab found reduced resting HRV in patients with normal peripheral vagal pathways.44 We found only one study that used a reflexive measure of vagal activity to assess the relationship between plasma IL-6 and caudal parasympathetic/vagal circuitry.