Report on “Radiation Disaster Recovery Studies”
Course : Radioactivity Social Recovery Course
Name : Tatsuru HONDA○Regarding“Radiation Disaster Recovery Studies”
Radiation disasters cause a wide range of impacts on the natural environment, thesocioeconomy, and the physical and mental health of the residents. According to reports from pastmajor nuclear accidents, it has been concluded that the long-term impact on the mental health ofresidents, in particular, is significant (WHO, 2005). One of the factors contributing to poor mental
health is anxiety about the adverse effects of radiation on physical health, and it has been observedthat residents' anxiety increases after radiation disasters (e.g., Fukasawa et al., 2017; Niitsu et al.,2014).
The development of such anxiety involves information obtained from the external
environment. For instance, a study examining the correlation between disaster-related informationfrom the media and the mental health of residents after a man-made disaster revealed that exposure
to such information enhances residents' anxiety (Vasterman et al., 2005). Moreover, research has
demonstrated that an increased volume of media reporting on disaster-related information intensifies
the risk perception (Renn et al., 1992). Another study investigating the relationship between disasterrelated information and radiation anxiety after the Fukushima Daiichi nuclear power plant (FDNPP)
accident revealed that individuals who relied on Internet media as their source of disaster-related
information were more anxious about radiation (Nakayama et al., 2019). Therefore, it is necessary totake disaster-related information into account when addressing the mental health of the residents inthe event of a radiation disaster.
From the perspective of information processing, when considering the relationship between
disaster-related information and anxiety, there is a possibility that the self-prioritization effect (SPE;1Sui et al., 2012) enhances the relationship between the two. The SPE refers to the phenomenon where
information relevant to oneself is prioritized over information that is not relevant. Specifically, it isknown that self-relevant information is more likely to be attended to and remembered (e.g., Moray,1959; Rogers et al., 1977). As our capacity to process information is limited, the SPE contributes tothe efficient acquisition of important information from the external environment. However, in thecase of radiation disasters, the SPE could contribute to heightened anxiety. Disaster-related
information, such as exposure risks and health effects, is considered self-relevant information
concerning one's physical health. Given that disaster-related information can contribute to thedevelopment of anxiety, prioritizing the processing of such information may lead to heightenedradiation anxiety.
Considering the role of the SPE in radiation disasters, gaining a deeper understanding of themechanisms that give rise to the SPE may offer insights into maintaining the mental health ofresidents during such disasters from an information processing perspective. Therefore, the factors
contributing to the emergence of the SPE were investigated in the doctoral thesis. Specifically, I
examined the influence of interoception, which refers to the sensation of the internal bodily states(e.g., Kobayashi et al., 2021), on the SPE, drawing on insights from previous studies.

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○Title of Doctoral Thesis

Impact of Interoception on the Self-Prioritization Effect○Summary of Doctoral Thesis
The FDNPP accident is also referred to as an information disaster, and it has beendemonstrated that information related to radiation disasters is closely linked to the development ofradiation anxiety among the residents (Nakayama et al., 2019). When considering the human
information processing, it is known that we selectively process external information based on its
relevance to ourselves, giving priority to self-relevant information (SPE; Sui et al., 2012). Radiationrelated information is crucial for avoiding the physical adverse effects of radiation, especially afterradiation disasters. Therefore, in such situations, the SPE can be considered a potential factor that
may further heighten radiation-related anxieties. However, the underlying mechanisms of the SPE
remain unclear. Gaining a deeper understanding of the SPE could provide insights into how to reduceradiation anxieties induced by disaster-related information.
When considering the mechanism underlying the emergence of the SPE, valuable insights
can be derived from research on its neural basis. Previous studies have indicated that the insularcortex is involved in the SPE (Qin et al., 2020; Zhang et al., 2023). Given that the insular cortex isclosely associated with the processing of interoception (Critchley et al., 2004), it suggests thatinteroception, sharing a common neural basis, may play a role in the emergence of the SPE. However,
the actual relationship between interoception and the SPE has not been examined. Therefore, thisstudies aims to gain a better understanding of the mechanism behind the emergence of the SPE andto examine the relationship between interoception and the SPE.
Study 1 examined the correlation between interoceptive sensibility, one of the individual
differences in interoception, and the SPE. Interoceptive sensibility refers to the awareness of changes
in interoceptive sensations in daily life and is assessed through self-report questionnaires (Garfinkelet al., 2015). However, no significant correlation was found between the two, indicating no evidence3

of an association between the SPE and interoceptive sensibility.
In Study 2, the relationship between interoceptive accuracy, another individual difference ininteroception, and the SPE was examined. Interoceptive accuracy refers to the ability to accurately
perceive interoception and is assessed through experimental tasks (Garfinkel et al., 2015).
Additionally, to investigate the impact of interoception on the SPE, external stimuli synchronizedwith the participants' cardiac cycle were presented during the task to measure the SPE. As a result,a significant negative correlation was observed between interoceptive accuracy and the SPE under
the cardiac systole condition, where external stimuli were synchronized with the interoceptive signals.
However, no significant correlation was found under the cardiac diastole condition, where suchsynchronization was absent. These findings suggest that interoception may inhibit the emergence of
the SPE. However, this cannot definitively rule out the possibility of a spurious correlation between
interoceptive accuracy and the SPE, considering they are both dependent variables. Additionally,
there is a concern regarding the validity of the task used to measure interoceptive accuracy.
Consequently, doubts remained regarding the suggested relationship in Study 2.
Therefore, in Study 3, to validate the findings obtained in Study 2, the relationship between
interoceptive accuracy and the SPE was examined by introducing a manipulation involving vagus
nerve stimulation, in addition to presenting stimuli synchronized with the cardiac systole. The resultof the experiment demonstrated that the SPE was more likely to emerge when the vagus nerve wasactivated, or in other words, when the processing of interoceptive signals was activated. In contrast
to Study 2, these result indicated that interoception facilitates the emergence of the SPE. The reason
for the different results between Study 2 and Study 3 can be attributed to the nature of theinteroceptive accuracy assessed in Study 2. It is speculated that in Study 2, interoceptive accuracy
reflected a tendency to process non-interoceptive signals as interoception, rather than accurately
perceiving interoception. In the processing of self-relevant information, the integration of external
stimuli and interoceptive signals is necessary. However, the interference caused by the noise might
have hindered the integrated processing of external stimuli and interoceptive signals, potentially4inhibiting the emergence of the SPE.
As a result of the series of studies, it has become evident that interoception enhances theemergence of the SPE. The SPE is a phenomenon that aids in the efficient acquisition of important
information from the external environment. However, there is a concern that when disaster-related
information heighten anxiety, the SPE may function as a risk factor that amplifies anxiety. The
fundamental insights gained from this thesis suggest the possibility of reducing anxiety caused by
the excessive prioritization of disaster-related information by modulating individual interoceptiveprocessing. The radiation disaster at the FDNPP is often referred to as an "information disaster," andthe role of disaster-related information in developing residents' anxiety is significant. Based on thefindings presented in this thesis, future practical investigations are expected to contribute to thepreservation of residents' mental health after radiation disasters, with a focus on the perspective ofinformation processing.

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