Published papers

The concept of alexithymia has garnered much attention in an attempt to understand the psychological mechanisms underlying the experience of feeling an emotion. In this study, we aimed to understand how the interoceptive processing in an emotional context relates to problems of alexithymia in recognizing self-emotions. Therefore, we prepared experimental conditions to induce emotional awareness based on interoceptive information. As such, we asked participants to be aware of interoception under an anxiety-generating situation anticipating pain, having them evaluate their subjective anxiety levels in this context. High alexithymia participants showed attenuated functional connectivity within their ‘interoception network’, particularly between the insula and the somatosensory areas when they focused on interoception. In contrast, they had enhanced functional connectivity between these regions when they focused on their anxiety about pain. Although access to somatic information is supposed to be more strongly activated while attending to interoception in the context of primary sensory processing, high alexithymia individuals were biased as this process was activated when they felt emotions, suggesting they recognize primitive and unprocessed bodily sensations as emotions. The paradoxical somatic information processing may reflect their brain function pathology for feeling emotions and their difficulty with context-dependent emotional control.

The insular cortex is considered an important region for feeling emotions through interoception. Most studies that report the role of the insula in integrating interoception and emotion have used neuroimaging techniques such as functional magnetic resonance imaging (fMRI); however, there are limited neuropsychological studies. The effects of insular lesions on emotion and interoception have not been suitably investigated. In this study, we examined the role of the insular cortex in cardiac interoception and recognizing emotions from facial expressions by comparing them pre- and post-operatively in patients with glial tumors or brain metastases associated with the insular lobe. Although no significant difference in interoceptive accuracy was observed between the two phases, there were significant associations between the changes in interoceptive accuracy and sensitivity to expressions of anger and happiness. An increased error rate in the heartbeat counting task in the post-operation phase was associated with a decreased accuracy in recognizing anger and happiness. Since most patients had left insula lesions, generalizability of the findings to patients with right lesions is a future subject. To the best of our knowledge, this is the first study to examine the change in interoception and emotion after insular resection in humans. The study results indicate that removal of the insula affects the recognition of emotions such as anger and happiness through interoceptive processing.

The conventional analysis assumes a constant mental state during scanning and assesses the strength of functional connectivity as the average of the entire fMRI data. However, it is suggested that even at rest, functional connectivity may change with time, and the conventional analysis has not been able to fully evaluate its properties. To overcome this limitation, many studies propose an index called dynamic functional connectivity (dFC) or time-varying functional connectivity (TVFC) or the chronnectome. This article reviews the significance and methods of dFC, examples of its application in clinical studies, and its limitations. Finally, we discuss its potential for clinical application.

Our thought states change without intention. This study verified that the transition of thought states varies with fluctuations in autonomic nervous activity, and that this effect is modulated by interoceptive accuracy. The participants completed the heartbeat counting task (HCT) and vigilance task. We assessed the participants’ interoceptive accuracy based on their performance on the HCT. The vigilance task is a simple attention task, and during this task, we asked the participants to report the content and contemplation of their thoughts. Consequently, participants with accurate interoception were more likely to remain in a highly contemplative thought state when parasympathetic activity was suppressed. In contrast, the dominance of parasympathetic activity facilitated transitions to different thought states or experiences of less contemplative thought states in them. The results suggest that even subtle changes in bodily responses at rest can affect thought transitions in people with accurate interoception.

Background: Major depressive disorder (MDD) is a highly prevalent psychiatric disorder marked by disrupted brain dynamics. However, the neural mechanisms underlying remission remain poorly understood, particularly regarding common neural markers across diverse therapeutic interventions. Emerging evidence suggests that temporal brain dynamics and their hierarchical organization, referred to as metastates, serve as sensitive markers of individual variability across cognitive functions. In this study, we evaluated whether metastate dynamics derived from resting-state functional magnetic resonance imaging (rs-fMRI) differed according to remission status across pharmacotherapy, psychotherapy, and neuromodulation. Methods: This multicenter observational study with 370 participants included 229 individuals with depression and 141 healthy control participants. The depression cohort comprised individuals undergoing cognitive behavioral therapy (n = 92), pharmacotherapy (n = 59), electroconvulsive therapy (n = 50), and repetitive transcranial magnetic stimulation (n = 28). rs-fMRI data were analyzed to derive metastate dynamics, and comparisons were made according to remission status across treatment modalities. Results: Two distinct metastates were identified, one associated with higher-order cognitive brain regions and another linked to sensory and motor systems. Participants who achieved remission exhibited greater predictability in transitions between brain states within metastates, supporting higher-order cognitive functions. This altered transition pattern was accompanied by alterations in the anticorrelation between the default mode and executive function networks, which may underlie the increased predictability. Conclusions: Remission from MDD may involve a reorganization of hierarchical brain dynamics—particularly in systems supporting cognitive control—and may offer a potential treatment modality–independent biomarker of remission.

Alexithymia has been widely associated with altered interoception, yet empirical findings remain inconsistent, partly because prior research has insufficiently examined the multidimensional components of interoception. This study aimed to provide a more comprehensive understanding of the relationship between alexithymia and interoception by independently examining the associations on interoceptive sensibility and interoceptive belief with alexithymia, while controlling for depression and trait anxiety. 86 undergraduate and graduate students completed questionnaires assessing alexithymia, interoceptive sensibility, depression, anxiety, and autistic traits. Interoceptive belief was measured using the Heart Rate Discrimination task, which provides psychophysical estimates of bias and precision in cardiac interoceptive judgements, alongside an exteroceptive condition. Results showed that alexithymia was selectively related to altered interoceptive belief. Difficulty describing feelings was associated with biased overestimation of cardiac activity, whereas externally oriented thinking was associated with reduced precision, indicating greater uncertainty in interoceptive belief. Path analysis further showed that reduced precision in interoceptive belief uniquely predicted externally oriented thinking, independent of depressive and anxiety symptoms. Interoceptive sensibility was evaluated using the Japanese version of the Multidimensional Assessment on Interoceptive Awareness. Results indicated that higher levels of alexithymia were associated with reduced adaptive interoceptive sensibility across multiple dimensions of bodily awareness. These findings suggest that while diminished interoceptive sensibility characterizes the subjective experience of alexithymia, altered interoceptive belief plays a more proximal role in its cognitive core, highlighting the importance of belief-based mechanisms in emotional inference.

Alexithymia is a multifaceted personality construct characterized by difficulties in identifying and describing emo- tions. Previous studies have argued that, among the multiple components of alexithymia, externally oriented thinking (EOT) is the only one related to Euro-American values. The current study examines whether, among three components of alexithymia, only EOT is related to Euro-American values. The study used survey data from 62 Chinese participants, who completed (a) image tasks measuring Euro-American values, (b) measures of Euro-American values (ICS), and (c) measures of alexithymia (TAS-20). A relationship was found between individuals’ total scores of alexithymia and Euro- American values, while no relationship was found between EOT and Euro-American value. These results show that EOT may not be the only component of alexithymia related to Euro-American values.

本稿は，女性の月経周期に伴う感情変動のメカニズムを，身体内部の情報を知覚する「内受容感覚」という視点から検討することを目的とした．従来，月経前の黄体期における不安や抑うつ，易怒性といった精神症状は，性ホルモンの変動に伴う中枢および末梢の神経活動の変化と関連付けて考えられることが多かった．しかし，同一の生理的変化が生じていても症状の現れ方には著しい個人差がある．この個人差の要因として，身体の状態を知覚する内受容感覚の処理プロセスに着目した．女性50名を対象に，卵胞期と黄体期の2回にわたり，自律神経活動の測定，心拍カウント課題による内受容感覚の正確さの評価，および心理尺度（MAIA，STAI，PMDD評価尺度）を用いた調査を実施した．分析の結果，安静時の心拍数には周期による差は見られなかったものの，自身の身体に注意を向ける心拍カウント課題時において，黄体期は卵胞期よりも交感神経活動が有意に高まることが示された．心理的側面では，黄体期における状態不安の増大は，身体感覚と感情の関連性に敏感な傾向（MAIA―因子5：感情への気づき」）と強い正の相関を示した．さらに，卵胞期において心拍を正確に知覚できる個人ほど，PMDD症状を強く自覚していることが明らかとなった．以上の結果から，内受容感覚を通じた身体状態の受容・解釈プロセスが，月経に伴うネガティブ感情の変動の個人差に関与している可能性が示唆された．内受容感覚という視点の導入により，個々の女性が自身の身体信号をどのように受け止め，感情や思考と統合しているかを解明する鍵となることが期待される．

Interoceptive accuracy is an index of the ability to perceive an individual's internal bodily state, including heartbeat and respiration. Individual differences in interoceptive accuracy influence emotional recognition through autonomic nervous activity. However, the precise mechanism by which interoceptive accuracy affects autonomic reactivity remains unclear. Here, we investigated how cardiac reactivity induced by a non-affective external rhythm differed among individuals, using a heartbeat counting task. Because individuals with poor interoceptive accuracy cannot distinguish an external rhythm from their cardiac cycles, it has been hypothesized that the interoceptive effect on heart rate works differently in individuals with good interoceptive accuracy and those with poor interoceptive accuracy. Study participants observed a visual or auditory stimulus presented at a rhythm similar to the participants' resting heart rates. The stimulus rhythm was gradually changed from that of their resting heart rate, and we recorded electrocardiographs while participants were exposed to the stimuli. Individuals with good interoceptive accuracy exhibited a deceleration in heart rate when the rhythm of the auditory stimulus changed. In contrast, in the group with poor interoceptive accuracy, the heart rate decreased only when the stimulus became faster. They were unable to distinguish the rhythm of their own heartbeat from that of the external rhythm; therefore, we propose that such individuals recognize the stimuli at the pace of their heart rate. Individuals with good interoceptive accuracy were able to distinguish their heart rates from the external rhythm. A modality difference was not observed in this study, which suggests that both visual and auditory stimuli help mimic heart rate. These results may provide physiological evidence that autonomic reactivity influences the perception of the internal bodily state, and that interoception and the autonomic state interact to some degree.

Research has discovered the modulatory effect of peripheral stimulation simulating altered bodily signals on emotion. Whether such an effect varies depending on one's interoceptive accuracy (IAc) remains unclear. Therefore, we provided haptic stimulation simulating participants’ slowed-down heartbeats or no stimulation while they engaged in socially stressful tasks to examine whether participants reacted differently depending on their IAc. Results showed that haptic stimulation exhibited the opposite effect on participants with different levels of IAc for both heart rate and heart rate variability (HRV). When receiving the stimulation, participants with higher IAc showed less increased heart rate and more elevated HF than participants with lower IAc. In contrast, in the absence of stimulation, an opposite pattern of response depending on participants’ IAc was observed. The modulatory effect of stimuli and IAc on prosocial behavior was not significant. Individual differences in IAc were shown to affect how one perceives/responds to altered bodily signals.

To clarify the feeling of knowing a name but not being able to recall it, known as having a “tip-of-the-tongue” (TOT) experience, we proposed a TOT model consisting of three stages combining a face recognition model and autonomic sympathetic nerve activity. Since TOT increases with age, we compared two age groups: young (N = 27, M = 20.4 ± 1.5 years) and middle-aged (N = 29, M = 58.5 ± 8.0 years). Experiment 1 showed that successfully naming low-frequency common names increased the skin conductance response (SCR) value, and the time to reach the maximum SCR value was longer. Experiment 2 was a naming task for face photographs. The younger group showed higher SCR values during successfully naming, while the middle-aged group showed similar SCR values for successfully naming and experiencing TOT. Both groups had the longest time to reach maximum SCR in TOT. In this study, physiological arousal of TOT was not affected by aging.

Our thought states shift from one state to another from moment to moment. The relationship between the thought shifting and bodily responses is yet to be directly examined. This exploratory study examined the influence of cardiovascular reactivity and interoception—sensing an internal bodily state—on the shifting of thought states. Participants (N = 100, 70 women) completed two tasks: the heartbeat counting task (HCT) and the vigilance task (VT). We assessed their interoceptive accuracy through their performance on the HCT. The VT was a simple sustained attention task in which participants pressed a key when the target stimulus appeared and were asked to report their thoughts. We presented subliminal vibration stimuli to induce alterations in heart rate (i.e., vibration block). Results showed that participants with higher interoceptive accuracy reported more continuation of self-referential thought (about past episodes and future plans regarding themselves) during the vibration block than did those with lower interoceptive accuracy. These results suggest that individuals with higher interoceptive accuracy are more likely to be influenced by their subliminal bodily response, resulting in divergent attention from the task and intermittent self-referential thought.

Cognitive behavioral therapy (CBT) is a psychotherapy that challenges distorted cognitions; however, the neural mechanisms that underpin CBT remain unclear. Hence, we aimed to assess the treatment-related resting-state functional connectivity (rsFC) changes in the brain regions associated with future thinking and the associations between rsFC changes and clinical improvements. Thirty-eight adult patients with MDD were randomly assigned with equal likelihood to receive 16-week individual CBT or talking control with a 12-month follow-up period. We evaluated the rsFC changes in the frontal regions, nucleus accumbens, amygdala, and limbic structures key to the depression pathophysiology and future thinking with 2 × 2 mixed ANOVA interaction analysis. Pearson's correlation analysis with Bonferroni's correction was also performed to examine the associations with clinical symptoms, such as depression severity and automatic thoughts in follow-up evaluations. Treatment-specific changes include enhancement in frontopolar connectivity with the nucleus accumbens. An increased rsFC was associated with lower negative automatic thoughts postoperatively, together with lower depressive symptoms and higher positive automatic thoughts at follow-up. Conclusively, rsFC changes in the fronto-limbic neural control circuit after CBT, particularly between the frontal pole and nucleus accumbens, may be clinically meaningful functional changes related to the depression recovery process.

Interoception has been proposed as a factor that influences various psychological processes (Khalsa et al., 2018). Afferent signals from the cardiovascular system vary across cardiac cycle phases. Heartbeat-evoked potentials (HEP) and event-related potentials (ERP) were measured to examine whether interoceptive signals differed between cardiac cycle phases. Simultaneously, participants performed an auditory oddball task in which the timing of the presenting stimulus was synchronized with the heartbeat. Pure tones were presented at 10 ms (late diastole condition), 200 ms (systole condition), or 500 ms after the R wave (diastole condition). Greater HEP amplitudes were observed when the tone was presented during diastole than during systole or late diastole. ERP showed the same tendency: a greater amplitude was observed during diastole than systole or late diastole. These results suggest that the processing of interoception reflected by HEP and exteroception reflected by ERP share attentional resources when both stimuli coincide. When the tone was presented during systole, attention to the internal state decreased compared with when the tone was presented during diastole, and attention was distributed to both exteroception and interoception. Our study suggests that HEP may be considered an indication of a relative amount of resources to process the interoception.