**4. Measurements at rest and during the task load**

In the studies on HRV in depression and anxiety, the data at rest condition have been frequently used to analyze the autonomic activity. And in some studies, the data were also recorded during task load or stress. An introduction of task load or stress enables the evaluation of autonomic responsiveness to the load. Random number generation task has been used for the task load in our studies. Random number generation is related to frontal cortical function. In the task, the subject makes a series of digit numbers (0–9) in random order at the speed of 1 Hz [10].

We propose to record HRV at rest (Rest), during task load (Task), and at rest after the task (After) (**Figure 5**). **Figure 5** shows sample data of a normal healthy subject. HF decreases, and LF/HF and HR increase during the task load. These changes of HRV are possibly related to the autonomic modulation in response to the task load and reflect both physical and mental adjustment to stress. Introduction of task load to the assessment of HRV has been found informative on analyzing the autonomic dysfunction of mental disorders [11]. The present chapter is intended to summarize that the Rest, Task, and After scores of HRV are differently altered in depression and anxiety.

Our previous study [12] has indicated the importance of analyzing the change from the rest data to that during the task load. Task/Rest ratio of the HRV indices is

**Figure 5.**

*A sample data of heart rate variability indices at the initial rest period (Rest), during the task load (Task), and during the rest period after the task (After).*

used for this purpose, especially for evaluating depressiveness and anxiety. In this study on normal subjects, subjective depressiveness and anxiety were scored by questionnaires; Self-rating Depression Scale (SDS) and State-Trait Anxiety Inventory (STAI) [12]. It has been revealed that the Task/Rest ratio of HF index is significantly correlated with both SDS and STAI scores, confirming the importance of Task/Rest ratio in evaluating depression and anxiety. Below are the HRV profiles of depression and anxiety showing different patterns in the Rest-Task-After paradigm.
