**2.2.4 NIRS data acquisition**

A dual-channel NIRS unit (NIRO-200; Hamamatsu Photonics K.K., Hamamatsu, Japan) was used to measure the temporal changes in oxy-Hb, deoxy-Hb, and total hemoglobin during the perspective taking task. Near-infrared light at three wavelengths (775, 850, and 910 nm) was used as the light source. The distance between the emitter and the detector was set to 4 or 5 cm. The sampling rate was 1 Hz.

The hemoglobin concentrations were calculated by subtraction from the baseline concentrations. Two probe holders were placed on the left and right sides of the forehead corresponding to the ventral area of the prefrontal cortex. These positions were localized between Fp1 and F7 (left) and between Fp2 and F8 (right), according to the international 10– 20 system.

#### **2.3 Results and discussion**

72 Infrared Spectroscopy – Life and Biomedical Sciences

facial expression. Participants in a pilot study rated each facial expression on a 5-level scale (0 = not at all to 4 = very intense) in terms of happiness and anger. The mean rating for the valence of the selected stimuli was 2.32 ± 0.73 for anger and 2.57 ± 0.89 for happiness. Furthermore, the intensity of each facial expression was rated and the rating scores for the intensity of all selected facial stimuli showing anger and happiness were 3.40 ± 0.92 and 3.15

First, as an orienting task, the relationship between the participants and six opponent players (two fair, two unfair, and two neutral players) was manipulated through a sequential Prisoner's Dilemma game controlled by a computer program. In each trial, the participants decided whether they cooperate with the opponent or not. If both the participant and the opponent decide to cooperate, they each earn 10 points; if both defect, neither earns any points. If the participant cooperates and the opponent defects, the participants loses 40 points and the opponent earns 40 points, and vice versa. The cooperation rates throughout all trials for the fair opponent, the neutral opponent, and the

The opponent's facial expressions were presented on a PC screen after the participants decided their selection. When both the participant and the opponent cooperated, the opponent's expression became happy; when both defected, the opponent's expression became angry. When the participant cooperated and the opponent defected, the opponent's expression became happy, whereas when the participant defected and the opponent cooperated, the opponent's expression became angry. After playing with each opponent, the participants evaluated the opponent on a 7-point scale ranging from "cooperative" to

After the orienting task, the participants performed a perspective-taking task with the NIRS device. A block design consisting of 12 blocks was used. The participants observed the facial expressions of the opponents under the two conditions of self-perspective and other's perspective. After a fixation point, the other's facial expression was shown for one second. The participants evaluated the valence of the facial expression on a 7-point scale from

A dual-channel NIRS unit (NIRO-200; Hamamatsu Photonics K.K., Hamamatsu, Japan) was used to measure the temporal changes in oxy-Hb, deoxy-Hb, and total hemoglobin during the perspective taking task. Near-infrared light at three wavelengths (775, 850, and 910 nm) was used as the light source. The distance between the emitter and the detector was set to 4

The hemoglobin concentrations were calculated by subtraction from the baseline concentrations. Two probe holders were placed on the left and right sides of the forehead corresponding to the ventral area of the prefrontal cortex. These positions were localized between Fp1 and F7 (left) and between Fp2 and F8 (right), according to the international 10–

unfair opponent were set in 80%, 50%, and 20%, respectively.

"pleasantness" to "unpleasantness" within two seconds.

"uncooperative" and "like" to "dislike."

**2.2.4 NIRS data acquisition** 

20 system.

or 5 cm. The sampling rate was 1 Hz.

± 0.86, respectively.

**2.2.3 Procedure** 

First, the orienting task confirmed that the operation of the social relationship between the participants and the opponents succeeded. The rating scores of "cooperativeness" showed that cooperative others were rated as more cooperative than uncooperative others and neutral others, while uncooperative others were rated as more uncooperative than cooperative others and neutral others. In the rating scores of "likeness," it was confirmed that the cooperative others were liked, whereas the uncooperative others were disliked.

#### **2.3.1 Behavioral data**

Figure 1 shows behavioral data of the pleasantness points in the perspective taking task. For the pleasantness points, a 2 × 3 × 3 (perspective taking, social relationship, and facial expression) analysis of variance (ANOVA) showed main effects of the three factors. The analysis also showed a significant 3-way interaction. The results showed that taking the other's perspective yielded no differences between high and low abilities of perspective taking. This indicated that the ability of perspective taking was not reflected in the behavioral data.

Further analyses of the interaction indicated that for the cooperative others in both the selfand other-perspective taking, the mean score in the happy condition was higher than that in the neutral and anger conditions, and the mean score in the neutral condition was higher than that in the anger condition (all *p <* .05). However, for the uncooperative others, these differences between facial expressions were only significant in the other-perspective taking. Note that in the self-perspective taking condition to uncooperative others, there was no difference among the rating scores of the three facial expressions.

Fig. 1. Behavioral evaluation of the validity of the mean value of each condition on a 7-point scale ranging from "pleasantness" to "unpleasantness." Adapted from Nomura et al. (2010).

Using NIRS to Investigate Social Relationship in Empathic Process 75

As described above, in line with individual differences in the ability of empathic processing, Nomura et al. (2010) revealed that for a person who has a high ability of perspective taking, the right VLPFC activates to take the other-perspective of the unfair other. Previous studies have presented evidence that the right VLPFC can modulate the activity of the amygdala even when emotional responses in the amygdala are implicitly evoked by emotional signals independent of the current conscious cognitive processing (Hariri, Bookheimer, &

According to these findings, the results reported by Nomura et al. (2010) suggest that the amygdala activation in the participants with high perspective-taking ability is suppressed while taking the perspective of an unfair person, and this leads to a decrease in their subjective negative emotions. The suppression of negative emotion is formed by the cognitive appraisal of the social behaviors of others by top-down processing. It was found that because participants with a higher perspective-taking ability evaluate the valence of emotions from the others' perspective when observing a happy facial expression by disliked others, they possibly use top-down intentional processing to effectively suppress the negative emotion evoked automatically by bottom-up processing. In contrast, participants with a lower perspective-taking ability could not suppress the negative emotion when they took the perspective of the disliked other. This reflects the decreased activation in the right VLPFC. In this way, the sensitivity to stimuli to evoke emotions varies according to the individual difference of the empathic ability, and this would produce different brain activities associated with the suppression of negative emotions. Further studies using fMRI and PET are needed to assess the neural basis related to the empathic process, including the

We finally describe the advantages and disadvantages of brain imaging techniques using NIRS. Although fMRI and PET also measure the local bloodstream of the brain, each of these NIRS devices has its own advantages and disadvantages and is chosen depending on

The disadvantage of NIRS in comparison with other imaging techniques is that the spatial resolution is lower. In addition, NIRS cannot measure deep parts of the brain such as the amygdala, brainstem, and cerebellum because brain tissues can only be measured approximately 3 cm from the surface of the head. Furthermore, it is difficult to identify the detailed anatomical position associated with brain function. The brain regions cannot be identified precisely from the scalp, and it becomes necessary to measure three-dimensional MR images in order to confirm the positions between the probes and brain regions. However, the positions of the probes can be determined according to the international 10-20 system for electroencephalogram recording, and at present, a number of studies using NIRS

On the other hand, NIRS has some strong advantages. First, it is highly non-invasive and thus safe. The burden on participants is relatively low, since they are not injected with

Mazziotta, 2000; Nomura, Ohira, Haneda, Iidaka, Sadato, Okada, & Yonekura, 2004).

**3.1 Neural mechanisms of empathic process and social relationships** 

**3. Conclusions and future directions** 

activity of the amygdala.

the purpose of research.

adopt this system.

**3.2 Application and prospects of NIRS** 

#### **2.3.2 NIRS data**

Figure 2 shows the mean concentration change of the oxy-Hb in the right VLPFC. For the NIRS data, a 2 × 2 × 3 × 2 (perspective taking ability, perspective taking, social relationship, and hemisphere) ANOVA showed a significant 4-way interaction. No main effect was found in any of the factors. In the unfair condition, the oxy-Hb concentrations significantly increased in the right VLPFC while taking the other's perspective as compared to the selfperspective (Figure 3). Accordingly, taking the other's perspective while perceiving the facial expressions of an unfair opponent significantly activated the right VLPFC only when the participants have high perspective-taking ability.

Fig. 2. Mean concentration changes in oxy-Hb during hemodynamic response in the right VLPFC. Adapted from Nomura et al. (2010).

Fig. 3. Averaged oxy-Hb concentration time changes in the right VLPFC hemodynamic response. Gray zone indicates task interval times and white zone indicates rest interval times in the unfair and other's perspective condition. Adapted from Nomura et al. (2010).
