The coronavirus disease 2019 (COVID-19) pandemic and quarantine have led to an increase in the number of people complaining of mental health problems. Depression, anxiety, and somatization symptoms increased at the outbreak’s peak in China [1
]. Other adverse mental health conditions have also been pointed out, such as fear and insomnia [2
]. Furthermore, some studies found that the impact of quarantine and isolation on mental health outcomes continued over a long period [4
]. In Japan, “mild lockdown”, which was not enforceable and a non-punitive lockdown, was implemented [5
]. Despite the loosely regulated lockdown, the number of railway users in the months under the mild lockdown decreased by 45.5% in April and 46.8% in May compared to each of the same months of the previous year [6
]. Regarding the psychological impacts of non-coercive lockdown, Yamamoto et al. (2020) found that 36.6% of participants experienced mild to moderate psychological distress (Kessler Psychological Distress Scale (K6) score of 5–12) and 11.5% experienced severe psychological distress (K6 ≥ 13) [5
]. Moreover, the estimated prevalence of depression (Patient Health Questionnaire-9 score ≥ 10) was 17.9% [5
Many reports show an increase in mental health deterioration under quarantine, as mentioned above. Furthermore, partial lockdowns have been implemented in many countries due to the second wave of infections. Therefore, it is urgent to clarify the causes of the increase in mental health deterioration and factors that promote these symptoms and take measures to combat them during the quarantine.
Interoceptive sensibility is one factor associated with psychological disorders such as depression, anxiety, and somatization symptoms. Interoception is the perception of one’s body’s internal state such as the body-to-brain axis of sensation concerning the state of the internal body and its visceral organs [8
]; the self-evaluated assessment of subjective interception is called interoceptive sensibility [8
]. Interoceptive sensibility appears to be affected by the quarantine restrictions due to the current pandemic, and this decrease is related to deterioration in mental health. During past pandemics, enhanced sensibility to one’s bodily sensations was observed. For example, during the 2009 H1N1 influenza pandemic, many hospitals’ reported being flooded with “worried well” patients who mistakenly believed that their benign coughs of fevers were signs of pandemic influenza [9
]. There is a concern about an increase in similar indefinite complaints in the current pandemic, and how to deal with them is an important issue [10
]. It is assumed that this tendency of interoceptive sensibility is strengthened by the prevalence of unknown infection diseases, and long-term quarantine, making it easier to pay attention to one’s bodily sensations. Indeed, Lucia et al. (2020) measured the degrees of depression, anxiety, and interoceptive sensibility assessed by the Self-Awareness Questionnaire [12
]. In a sample of amyotrophic lateral sclerosis (ALS) patients in March and April under the pandemic, it was found that all of the scales significantly increased in ALS patients compared to January and February before the pandemic [13
]. The results suggest that interoceptive sensibility is enhanced during the lockdown and is related to mental health even under the current pandemic.
Most of the previous studies on interoceptive sensibility dealt with one aspect of interoceptive sensibility: paying attention to one’s bodily sensations is related to the onset of psychological disorders. However, recently, it has been argued that it is essential to understand interoceptive sensibility from multiple perspectives [14
Interoceptive sensibility can be classified into two types depending on how people pay attention to interoception: the attention style based on anxiety and hypervigilance, and the mindfulness attention style [14
]. The former view was common in the past, and paying attention to bodily sensations was regarded as maladaptive. Attention to somatic symptoms in clinical groups was regarded as representing anxiety, depression, and somatization symptoms [15
]. Furthermore, in the study of anxiety and panic disorders, the terms “Body awareness” and “Somatic awareness” were used to describe cognitive attitudes characterized by an exaggerated focus on physical symptoms, somatosensory amplification, rumination, and catastrophic beliefs [16
]. However, paying attention to bodily sensations is regarded as useful for health in the latter view [17
]. Clinical research has pointed out that paying attention to bodily sensations such as mindfulness-based therapies in patients with various diseases leads to health benefits [18
] and resilience-enhancing [14
The Multidimensional Assessment of Interoceptive Awareness (MAIA) [17
] was developed based on the background that there are two different interpretations of interoceptive sensibility, as mentioned above. The MAIA is a multidimensional self-report measure of interoceptive sensibility and consists of eight subscales: (1) Noticing, (2) Not-Distracting, (3) Not-Worrying, (4) Attention Regulation, (5) Emotional Awareness, (6) Self-Regulation, (7) Body-Listening, and (8) Trusting (Table 1
). Although Noticing has been viewed as a subscale that does not distinguish between adaptive and maladaptive aspects [14
], the subscale resembles previous scales developed based on the view that paying attention to bodily sensations exacerbates anxiety and hypochondriasis [14
]. Thus, it can be considered to mainly measure the maladaptive aspect of interoceptive sensibility. Regarding the other subscales, it is said that they are about a mindful attention style [14
], so they can be considered to measure adaptive aspects of interoceptive sensibility. Therefore, focusing on the adaptive and maladaptive aspects of interoceptive sensibility by using the MAIA can be used to comprehensively understand the effects of each element of interoceptive sensibility on people’s mental health.
Few studies have investigated the effects of interoceptive sensibility on mental health during the lockdown. In addition, it is not clear how each aspect of interoceptive sensibility is associated with psychological and somatic symptoms. Hence, in the present study, we aimed to examine how adaptive and maladaptive aspects of interoceptive sensibility affect depression, anxiety, and somatization symptoms under the mild lockdown related to the COVID-19 pandemic. We hypothesized that Noticing is associated with increased psychological and somatic symptoms. At the same time, the other seven subscales are associated with a decrease in these symptoms.
The purpose of this study was to examine how adaptive and maladaptive aspects of interoceptive sensibility affect depression, anxiety, and somatization symptoms under the mild lockdown related to the COVID-19 pandemic.
The hypotheses were generally supported: Noticing was significantly associated with increased maladaptive symptoms such as depression, anxiety, and somatization symptoms. Conversely, many of the other subscales of the MAIA were significantly associated with a decrease in these maladaptive symptoms. Regarding Noticing, the results of the present study are consistent with the view of previous studies. In earlier studies of interoceptive sensibility, Noticing was regarded to be the same as the aspect assessed by the questionnaires [33
], and these questionnaires are related to mental disorders such as anxiety disorder (e.g., Steven Porge’s Body Perception Questionnaire [34
]). In considering the consistency between our study’s results and those of previous studies, it is suggested that Noticing, which is considered to represent a maladaptive aspect of interoceptive sensibility, contributed to the increase of psychological and somatic symptoms even during the mild lockdown.
Conversely, Not-Distracting, Not-Worrying, Self-Regulation, and Trusting significantly contributed to the decrease in the PHQ-9, SHAI, and SSS-8. Moreover, Attention Regulation significantly contributed to the decrease in SHAI. As hypothesized, it was found that adaptive aspects of interoceptive sensibility had positive impacts on mental health even during the mild lockdown. Both de Jong et al. (2016) [35
] and Bornemann et al. (2015) [33
] proposed the effectiveness of mindfulness-based cognitive therapy and contemplative training for improving these adaptive aspects. These mindfulness-based interventions can be conducted at home, so they would be effective as training that we can work on during mild lockdowns.
However, some results differed from the hypotheses. Body Listening significantly contributed to the increase in the PHQ-9, SHAI, and SSS-8. Further, Emotional Awareness significantly contributed to the increase in the PHQ-9 and SSS-8. Both subscales have been regarded as adaptive aspects of interoceptive sensibility, but they negatively affected mental health in the present study. A possible reason behind these negative associations is that catastrophic thoughts about bodily sensations could be related. Both Body Listening and Emotional Awareness had significantly negative correlations with Not-Distracting (Body Listening: r
= −0.21; Emotional Awareness: r
= −0.29, all p
s < 0.001). Therefore, these results indicate that higher Body Listening and higher Emotional Awareness is related to Distracting. Distracting from unpleasant bodily sensations is a common coping style that people with panic disorder [36
] or chronic pain [14
] often use. One reason this coping style is used is that people with panic disorder are susceptible to bodily sensations such as heartbeat. It is said that they often have catastrophic thoughts about these sensations and avoid these sensations because they see them as threatening [35
]. Even in people with chronic pain, the Fear-Avoidance Model [37
] explains the same things. This model most widely has been used to explain how chronic pain is sustained and deteriorates [38
], and assumes catastrophic thoughts about bodily sensations and concomitant avoidance towards these bodily signals. A recent study also assumed these characteristics in this model [38
]. Hence, the negative correlations of Body Listening and Emotional Awareness with Not-Distracting could imply that people exhibit catastrophic thoughts about bodily sensations. Although we pointed out the possibility that catastrophic thoughts existed as a background factor for the relationship between psychological or physical symptoms and Body Listening and Emotional Awareness, our research is not sufficient for determining this causal relationship. Therefore, it is necessary to investigate whether this relationship is observed by conducting a longitudinal study.
When future research determines the effects of catastrophic thoughts, interventions to mitigate them would be necessary. To alleviate catastrophic thinking toward bodily sensations, active exposures to interoception can be an effective intervention. Interoceptive exposures are applied to lessen panic attacks, which create a pseudo-oxygen-deprived state by exercise-induced increase in heart rate and breathing through straws [39
]. These interventions aim to ease catastrophic thinking by repeatedly inducing and enduring bodily sensations and increasing coping potential [39
]. Physical exercise is beneficial for physical and mental health and is recommended even during pandemic quarantine [41
]. These interventions can be done quickly, even during quarantine, to be useful as a personal effort to alleviate catastrophic thoughts.
The limitations of the present study are that although the survey was conducted during the mild lockdown, we did not take the exact number of days that individuals refrained from going out of their homes into account. Since the number of railway users under the mild lockdown decreased significantly, a large-scale tendency to refrain from going out was observed, but we did not examine the exact difference in individuals’ tendency to refrain from going out. Another limitation of the present study is that the causal relationship cannot be clarified because the survey was conducted at a single point in time. A follow-up study needs to be undertaken to examine this.
To the best of our knowledge, despite these limitations, this is the first study that focused on adaptive and maladaptive aspects of interoceptive sensibility and showed that each element had different mental health effects during the mild lockdown. Moreover, it was suggested that catastrophic thinking about bodily sensations might be increasing due to the current pandemic. The present study’s findings are essential as it highlights one of the secondary issues related to the current pandemic.