動物實驗顯示HRV降低(而非心跳加速)是恐懼感的最佳指標, HRV降低分為節奏性(第一階段)及變化性(第二階段),其中第一階段的持續時間決定恐懼感是否轉變為長期
Changes in heart rate variability are associated with expression of short-term and long-term contextual and cued fear memories.
PLoS One. 2013; 8(5):e63590 (ISSN: 1932-6203)
Liu J; Wei W; Kuang H; Zhao F; Tsien JZ
Key Laboratory of Brain Functional Genomics (Ministry of Education), Institute of Brain Functional Genomics, East China Normal University, Shanghai, China ; Brain and Behavior Discovery Institute and Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, United States of America.

Heart physiology is a highly useful indicator for measuring not only physical states, but also emotional changes in animals. Yet changes of heart rate variability during fear conditioning have not been systematically studied in mice. Here, we investigated changes in heart rate and heart rate variability in both short-term and long-term contextual and cued fear conditioning. We found that while fear conditioning could increase heart rate, the most significant change was the reduction in heart rate variability which could be further divided into two distinct stages: a highly rhythmic phase (stage-I) and a more variable phase (stage-II). We showed that the time duration of the stage-I rhythmic phase were sensitive enough to reflect the transition from short-term to long-term fear memories. Moreover, it could also detect fear extinction effect during the repeated tone recall. These results suggest that heart rate variability is a valuable physiological indicator for sensitively measuring the consolidation and expression of fear memories in mice.