Introduction
Recent research suggests an association between interoceptive deficits on the one hand and suicide ideation and suicidal behavior on the other hand [
1,
2]. Interoception is the ability to effectively perceive the physiological condition of the body [
3,
4]. Garfinkel and Critchley [
5] proposed to differentiate between
interoceptive accuracy, i.e. the ability of perceiving physiological sensations,
interoceptive sensibility, i.e. judgements of one’s dispositional ability to perceive body sensations, and
interoceptive awareness, referring to an individual’s metacognitive awareness of his interoceptive accuracy. Recent research found that the three facets of interoception are related but yet distinct constructs [
6‐
8]. Furthermore, Forkmann and colleagues [
6] argued for the integration of a fourth facet of interoception, i.e. the ability to correctly monitor and evaluate physiological states, such as the individual’s heart rate, which is supposed to be the most basic level of interoceptive signal processing.
Forrest et al. [[
2]; study I] compared interoceptive sensibility in controls, suicide ideators, suicide planners and attempters. In an online study, they found that those suffering from suicide ideation or behavior reported lower interoceptive sensibility than controls. Moreover, attempters stated lower interoceptive sensibility than planners or ideators. In a second study including psychiatric outpatients, self-reported interoceptive sensibility deficits were greater among those who attempted suicide compared to those who only thought about or planned suicide [[
2]; study II]. Furthermore, Dodd et al. [
1] provided evidence suggesting that impaired interoceptive sensibility is related to suicide attempts indirectly through mediating variables such as non-suicidal self-injury. These findings suggest that persons suffering from suicide ideation and behavior have greater difficulties of being in touch with their own bodily experiences. On this background, Forrest et al. [
2] speculate that being “disconnected from one’s bodily self, facilitates suicide attempts for those who desire suicide” (p. 755).
However, both studies [
1,
2] assessed interoceptive sensibility, i.e. subjective judgments of one’s dispositional tendency to be internally focused, using a rating scale and did not include a psychophysiological measure of interoceptive accuracy. Furthermore, both studies used an inconclusive self-report measure of interoceptive sensibility, the Interoceptive Awareness subscale of the Eating Disorder Inventory [
9]. This scale is primarily targeted to assess two types of physiological sensations, emotional and gastrointestinal sensations, but less to measure interoceptive sensibility. Only recently, Rogers, Hagan and Joiner [
10] used the Multidimensional Assessment of Interoceptive Awareness [MAIA [
11];] to measure interoceptive sensibility more broadly in a large sample (
N > 500) of adult participants with suicidal ideation/ behavior across the entire spectrum of the suicidality continuum. They found no differences in interoceptive sensibility between individuals with lifetime suicidal ideation, plans or attempts. Participants with lifetime suicidal ideation reported higher scores in worrying about body sensations than nonsuicidal participants. In addition, self-reported interoceptive deficits in terms of ignoring or distracting oneself from uncomfortable or painful body sensations and impaired self-regulation were larger in persons with lifetime suicide attempts compared to participants without a history of suicidal ideation/ behavior. Overall, participants with any history of suicidal ideation/ behavior trusted their bodily sensations less than nonsuicidal participants.
Although the study by Rogers and colleagues [
10] provided a more detailed analysis of the relation between different aspects of interoceptive sensibility and suicide ideation/behavior, there has been no research on markers of interoceptive accuracy in terms of the performance in correctly sensing bodily sensations. Since prior research suggests that there are different facets of interoception, measured with different methodological approaches, it is possible that interoceptive accuracy relates differently to suicidal ideation and behavior than interoceptive sensibility. An interoceptive accuracy task allows for a more objective assessment of interoceptive performance deficits and might thus be a more suitable indicator of potentially impaired interoceptive processing in persons with suicidal ideation/ behavior than questionnaires.
Another important variable that has not been considered in prior investigations on the relationship between interoception and suicidal ideation/behavior is depression. Depression has also been shown to be related to interoception: People with elevated depression scores tend to have lower interoceptive accuracy [
12‐
14]. Since suicidal ideation/ behavior and depression often co-occur [
15], it is important to control for depression when investigating the relationship between suicidal ideation/ behavior and interoception. Only recently, a first study was published that controlled for depression while investigating the relation between interoception and suicidal ideation [
16]. The reported results are mixed: when controlling for depression, only in two out of seven samples, a significant relation between interoceptive deficits and suicidal ideation were found.
Therefore, the aim of the present study was to assess interoceptive accuracy, using a heartbeat perception task, and interoceptive sensibility, using a comprehensive self-report measure while controlling for depression, in a heterogenous sample of subjects with or without current suicide ideation and with and without a Major Depressive Disorder (MDD). The results reported by Rogers et al. [
10] suggest that differences in interoception should most likely be found between non-suicidal controls and participants with suicidal ideation, but not between participants with suicide ideation and those who attempted suicide. Thus, investigating interoceptive deficits in patients with suicide ideation compared to non-suicidal controls appears appropriate. In line with prior investigations, we expected persons with suicidal ideation to have lower interoceptive sensibility and accuracy than persons without suicidal ideation. Moreover, depression was expected to be related to both suicidal ideation and indicators of interoception.
Discussion
The present study is, to the best of our knowledge, the first that investigated both interoceptive accuracy and sensibility while controlling for depressive symptoms in suicide ideators and healthy controls. Results suggest that suicide ideators are as competent in sensing their bodily signals as non-ideators when assessed with a psychophysiological measure of interoceptive accuracy. Suicide ideators report lower values in some indicators of interoceptive sensibility (MAIA) than non-ideators. However, these differences disappear when regression analyses were controlled for depressive symptoms. Moreover, when controlling for depression in a multivariate linear regression analysis it emerged that suicide ideators tend to worry more about their body sensations than non-ideators.
Using the same instrument (i.e., MAIA) to assess interoceptive sensibility as in the present study, Rogers et al. [
10] found that individuals with lifetime suicide ideation reported more worry about their bodily sensations than people without a lifetime history of suicidality. People with lifetime suicide attempts tended to ignore and distract themselves more from painful or uncomfortable bodily sensations than non-suicidal participants. Participants with any kind of suicidality (regardless of whether reported lifetime ideation, plans, or attempts) reported less trust of their bodily sensations. There were no differences in the other scales of the MAIA. In the present study, we investigated people with suicide ideation in the past 2 weeks in comparison to non-suicidal controls. Thus, the present sample is not fully comparable to the suicide ideators sample in the study by Rogers et al. [
10]. However, similarly to Rogers et al. [
10], we found a difference between non-ideators and ideators in the extent of reported trust in their own body - although both groups showed similar performance in an interoceptive task (i.e., HPT). Those participants who reported suicide ideation in the past 2 weeks trusted their bodily signals less. Moreover, ideators reported to be less able to sustain and control attention to body sensations, to regulate distress by attention to body sensations, and to listen actively to the body in order to gain more insight. Notably, all these aspects of interoceptive sensibility do refer to the ability to act on one’s own sensations in order to regulate attention or distress and not to the ability to gather information from one’s own body [
11]. This partly corresponds to results from Rogers et al. [
10] and the HPT results measuring interoceptive accuracy in the present study: both in terms of interoceptive accuracy and interoceptive sensibility, suicide ideators appear to be able to sense their bodily signals as well as non-ideators. However, in the MAIA (as a measure of interoceptive sensibility) they report that they are less able to act on them or use them functionally to regulate distress, which, ultimately, coincides with impaired body trust. Low body trust most likely leads to non-use of information from the body, an assumption that is corroborated by the result that suicide ideators report less body listening than non-ideators.
A considerable line of research suggests that access to and usage of information from the body is associated with better performance in memory [
27], learning [
28], and attention tasks [
29], less depression [
14,
30], more adaptive cardio-vascular responses to stress [
31], fewer difficulties in self-reported and objective decision-making [
32,
33], and, by trend, with less brooding rumination [
34]. Consequently, impaired body trust and little listening to the body may coincide with deficits in these variables. The Integrative Motivational-Volitional Model of Suicide [IMV [
35,
36];] proposes that memory deficits and biases, problem-solving deficits and perseverative thinking may contribute to the formation of suicidal thoughts and plans. Empirical evidence supports the main predictions of the IMV-model [
37,
38]. Thus, our results of low self-reported body trust and body listening, which probably leads to deficient use of available interoceptive information from the body, may be seen as in line with the assumptions of the IMV-model: deficient use of interoceptive information might lead to problems in decision-making, problem-solving, and memory and to heightened rumination and, in turn, contribute to the development of suicide ideation. Of course, this line of reasoning should be further investigated in future studies.
The results that suicide ideators reported lower abilities to sustain and control attention to body sensations and to regulate distress by attention to body sensations compared to non-ideators may indicate a potential mechanism contributing to the development and maintenance of suicide ideation. Recent research suggests that people with suicide ideation benefit from Mindfulness-based Cognitive Therapy [MBCT [
39‐
42];], which combines cognitive-behavioral elements such as psychoeducation with meditation. Thus, people with suicide ideation benefit from an intervention that teaches them to deliberately direct attention to body sensations and to
use body sensations (especially one’s own breath) to regulate their state of mind. This might indirectly be interpreted as suggesting that impaired abilities to sustain and control attention to body sensations and to regulate distress by attention to body sensations contributes to the development and maintenance of suicide ideation. Future research could address this issue more directly.
Table
2 shows that,
generally, participants with suicide ideation reported lower levels of abilities than participants without suicide ideation. Group differences could also be considered as reflecting a general tendency of suicidal persons to be less self-confident than non-suicidal persons: suicidal persons could tend to ascribe themselves low capabilities, regardless of what concrete ability they might be asked for. Research showing that suicidal ideation/ behavior is related to low self-confidence could be considered as being in line with this interpretation [
43].
However, when appreciating these results, it is of utmost importance to keep in mind that most differences between ideators and non-ideators vanished when controlling for depression. Thus, differences between suicide ideators and non-ideators could be overshadowed by a depression bias. Future research should aim at replicating the current findings and at investigating whether potential deficits in interoceptive sensibility are driven by heightened depression severity alone. Moreover, studies are lacking that investigate the interoceptive
awareness which has not been studied in people with suicidal ideation/ behavior at all [
5,
6].
Limitations
Some strengths and weaknesses of the current study have to be kept in mind when appreciating the reported results. This is the first study that investigated a measure of interoceptive accuracy in suicide ideators. Results were controlled for depression and the participants reported reasonable divergent levels of depression severity. A limitation is that suicide ideation was assessed with a single item instead of a more comprehensive method to assess suicide ideation. Yet, there is strong evidence for the predictive ability and relevance of single items assessing suicide ideation [
44]. Second, no suicide planners or attempters were included in the present investigation. Although prior research found no differences between suicide ideators, planners and attempters in terms of interoceptive sensibility [
10] these patients could likely have differed in terms of interoceptive accuracy. Future research should aim at replicating our findings in a sample covering the entire spectrum of suicidality. Third, the present study and all prior studies on the relation between interoception and suicidality were cross-sectional [
1,
2,
10]. However, the cross-sectional design limits the interpretation of the results as no causal conclusions can be drawn. Future studies should apply prospective designs in order to clarify whether interoceptive deficits are a risk factor for the development of suicidal ideation and behavior, contribute to its maintenance, or are a consequence of a suicidal development. Fourth, all participating patients were assessed in the hospitals where they were treated. As measurements had to fit in the schedule of the respective units where the patients were treated, unfortunately, it was not possible to control for room temperature and time of the day for the physiological assessments. Lastly, some scales of the MAIA had poor internal consistency in the current sample. Thus, reliability of assessments with these scales was limited.
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