**3. EKG: humans**

We believed that crustacean heartbeat continuously persists beating, that is, their hearts beat like the human heart does. But it was not the case (**Figure 7**). With EKGs from freely moving lobsters/crabs, we found that the heartbeat pattern is not continuous but intermittent if animals are not disturbed (**Figure 7**). This intermittency is induced by the activity of cardioinhibitory nerve (**Figure 8**, [12]). Then, EKG analysis revealed that a relaxed lobster exhibits an SI near 1.0 and a nervous lobster exhibits an SI near 0.5 (**Figure 9**). These results suggested

12 Time Series Analysis and Applications

**Figure 8.** Simultaneous electro-physiological recording: heart (pacemaker, largest spike size, approximately 3 mV), cardio-regulatory nerve (autonomic impulses, largest spike size, approximately 500 micro-V), and mechanical transducer (myocardial force, the largest peak force of contraction is approximately 1 mg). An increase of a nerve activity corresponds to a complete stop of heartbeat. The smallest spikes in amplitude are the cardio-inhibitory impulses. The other two include the cardio-acceleratory impulses. Hermit crab (*Aniculus aniculus)* (modified from Yazawa and Kuwasawa [12]).

**Figure 9.** A long EKG recording. Lobster, *Panulirus japonicus*. A human visit (thick lines) changes the heartbeat pattern. In relaxed and nervous conditions: SI ≒ 1 and SI ≒ 0.6, respectively (upper inset). SI distinguishes lobster's psychology.

All experimental subjects were treated as per the ethical control regulations of universities (Tokyo Metropolitan University; Tokyo Women's Medical University; Universitas Advent Indonesia, Bandung; Universitas Airlangga, Surabaya, Indonesia).

We have tested so far over 500 human individuals [5]. We have learned that SI is a useful indicator for job-related stress and/or contentment of everyday life, as well as for heart disease. Typical results from them are shown in **Table 1** (modified from Ref. [4]). When subjects reply to an interview that stress level is fairly low, the person's SI is near 1.0. In turn, subjects who have stress exhibit a low SI such as 0.7–0.8 (**Table 1**). Subjects who have ischaemic heart disease, that is, having damaged myocardium, have a high SI such as 1.2–1.4 (**Table 1**). It is worth noting that we found a correlation between a high SI and myocardial damage, when we conducted crustacean experiments (**Figures 5** and **6**).


**Table 1.** Typical mDFA results.
