The Granger Causality Analysis Between Acupoints in the Same Meridian Based on Skin Conductance

The granger causality analysis is a widely used statistical method of interpreting how different units work together to realize certain functions. It indicates how one time series impacts another under a certain time lag order. For different Acupoints (APs) in Traditional Chinese Medicine (TCM), some researchers begin to regard them as a complex and unified dynamic system and try to understand the hidden mechanisms. In this work, we adopt the granger causality analysis on APs' skin conductance to explore whether there are interdependencies between them, especially for those located in the same meridian. The results show that the causal relations between APs vary from different meridians, in particular for APs in the Lung meridian, the causal relations are much more obvious. Additionally, the average time lag order of the granger causality analysis from APs with smaller IDs to larger ones are greater than vice versa, which may be consistent with the flowing directions of the meridians. Moreover, the closer the APs are in the same meridian, the smaller the time lag order. The work proves the granger causality analysis as a powerful method of underpinning the functions of APs in the same meridian. In the future, more explorations of the internal cooperation between different APs could be made based on skin conductance, to provide scientific basis for TCM APs and meridians.

I. Introduction

According to the Traditional Chinese Medicine (TCM) theories, acupoints (APs) serve as significant foundations upon which the internal changes of human bodies could be reflected [1]. There have been a plethora of studies highlighting the role of APs in the early detection and effective treatment of diseases [2]–[4]. In the context of the scientific development of TCM, scholars and scientists hold ambitions to explain the implicit mechanisms of APs with modern technologies. For example, since Yoshio Nakatani et al. first proposed the “Ryodoraku” phenomenon in the 1950s, the specificity research of APs based on electrical signals has enjoyed an increasing uptake [5]. In the 1980s, Zhu et al. successfully located 14 meridians in the human bodies with the help of biophysical methods including the collected electrical signals at APs [6].