From Body to Brain and Back: Multimodal Evidence for Interoceptive Alterations in Schizophrenia Spectrum Disorders

This study demonstrates that schizophrenia spectrum disorders are characterized by pervasive, trait-like interoceptive disturbances, including impaired subjective bodily regulation, marginally reduced accuracy, and attenuated neural processing of cardiac signals, which are most consistently linked to depersonalization symptoms.

The Gist

The Big Picture: A Broken Radio Connection

Imagine your brain is a radio station and your body is the microphone. Usually, the microphone sends clear signals about what's happening inside you (like your heart beating or your stomach growling) to the radio station. The radio station then uses this info to help you feel safe, understand your emotions, and know that "I am me."

In people with Schizophrenia Spectrum Disorders (SSD), the researchers wanted to see if this connection between the body and the brain was "static-filled" or broken. They called this connection interoception—the ability to feel your insides.

The study asked: Do people with SSD hear their own body signals differently than healthy people? Does this difference explain why they feel disconnected from reality?

The Experiment: Three Ways to Listen

The researchers didn't just ask people how they felt; they looked at three different levels of "listening," like checking a radio at three different stages:

1. The "What I Think" Level (Subjective): They asked participants to fill out surveys about how much they notice their body, how much they trust it, and if they feel detached from it (like watching themselves from outside).
2. The "What I Can Do" Level (Behavioral): They gave participants a "heartbeat counting game." Participants had to close their eyes and silently count their heartbeats for a few minutes without feeling their pulse. Then, the researchers compared their count to the actual number of beats.
3. The "What the Brain Does" Level (Neural): They hooked participants up to an EEG (a cap with sensors) to watch their brain waves. Specifically, they looked for a tiny electrical spark in the brain that happens right after the heart beats. This is called a Heartbeat Evoked Potential (HEP). Think of this as seeing if the radio station actually receives the signal from the microphone.

What They Found

1. The "Feeling" Level: Confused and Distant

• The Finding: People with SSD reported feeling less in control of their body signals. They felt less trusting of their body and had more trouble regulating their emotions based on those signals.
• The Analogy: Imagine you are driving a car, but the dashboard lights are flickering, and the steering wheel feels slippery. You don't trust the car anymore.
• The Big Surprise: The strongest link they found was with depersonalization. This is the feeling that you aren't real, or that you are watching yourself from a distance. The more severe a person's symptoms were, the more they felt this "detached" feeling. It's like the radio signal is so weak that the listener feels like they are in a different room than the music.

2. The "Counting" Level: Slightly Off-Beat

• The Finding: When it came to the heartbeat counting game, people with SSD were slightly worse at counting their heartbeats than healthy people, but the difference wasn't huge. It was a "marginal" difference.
• The Analogy: If you asked a healthy person to count the seconds in a minute, they'd be pretty close. If you asked someone with SSD, they might be off by a few seconds. It's not a total failure, just a bit less precise.

3. The "Brain Signal" Level: It Depends on the Task

This was the most interesting part. The researchers looked for the brain's electrical spark (HEP) in two situations:

• Situation A: Just sitting quietly with eyes closed.
  • Result: No difference. The brain signals looked the same for both groups.
  • Analogy: When the radio is just sitting on the table doing nothing, the static is the same for everyone.
• Situation B: Actively trying to listen to the heartbeat (the counting game) or looking at a cross.
  • Result: Big difference! When people with SSD tried to focus on their heart, their brain signals were much weaker. The "spark" was dimmer.
  • Analogy: It's like a radio that works fine when it's off, but the moment you try to tune into a specific station (focus on the body), the signal drops out. The brain struggles to process the body's message only when it's being asked to pay attention to it.

What This Means (According to the Paper)

The paper concludes that the problem isn't that the body is "broken" or that the brain is always "static-filled." Instead, the problem is context-dependent.

• The "Trait" Idea: The feeling of being disconnected from your body (depersonalization) seems to be a core, stable part of the disorder. It's like a permanent crack in the windshield that makes the view blurry all the time.
• The "State" Idea: The brain's ability to process body signals gets worse specifically when you have to focus on them. It's not that the radio is broken; it's that the tuning mechanism gets overwhelmed when you try to listen closely.

Summary

The study suggests that for people with Schizophrenia Spectrum Disorders, the link between body and brain is shaky. They often feel like they are floating outside their bodies (depersonalization). While their brain can handle body signals when they are just relaxing, it struggles to process those signals when they are actively trying to focus on them. This suggests that the "glitch" happens when the brain tries to integrate body feelings with the rest of the world, rather than being a constant, background error.

Technical Summary

Technical Summary: "From Body to Brain and Back: Multimodal Evidence for Interoceptive Alterations in Schizophrenia Spectrum Disorders"

Problem Statement
Schizophrenia spectrum disorders (SSD) are characterized by disruptions in bodily self-consciousness, ranging from heightened, misinterpreted internal sensations (positive symptoms) to reduced bodily awareness and social withdrawal (negative symptoms). While interoception—the processing of internal bodily signals—is hypothesized to be central to these disturbances, empirical evidence remains fragmented. Previous literature presents inconsistent findings regarding the direction of interoceptive alterations (e.g., increased vs. decreased awareness) and lacks integrated investigations across subjective, behavioral, and neural domains. Furthermore, neuroimaging evidence regarding Heartbeat Evoked Potentials (HEP) in SSD is heterogeneous, with conflicting reports on whether HEP amplitudes are increased or decreased and whether these alterations are context-independent or task-dependent. This study addresses the need for a multimodal, cross-sectional investigation to clarify the nature of interoceptive dysfunction in SSD.

Methodology
The study employed a cross-sectional observational design comparing 53 patients with SSD (diagnosed via ICD-10, stable on antipsychotic medication) and 60 matched healthy controls (HC). Participants underwent a comprehensive assessment protocol including:

1. Subjective Measures: Self-reported interoceptive awareness was assessed using the Multidimensional Assessment of Interoceptive Awareness Version 2 (MAIA-2) and the Body Perception Questionnaire–Short Form (BPQ-SF). Depersonalization was measured via the Cambridge Depersonalization Scale (CDS).
2. Behavioral Measures: Interoceptive accuracy was quantified using the Heartbeat Counting Task (HCT), where participants counted perceived heartbeats over varying intervals.
3. Neural Measures: Simultaneous EEG and ECG recordings were obtained during three conditions: eyes-closed rest, eyes-open rest, and the HCT. HEPs were derived as time-locked cortical responses to R-peaks.
4. Statistical Approach:
   • Confirmatory Analyses: Pre-registered linear models and regressions tested group differences in self-reports, HCT accuracy, and HEP amplitudes at specific right-frontal regions of interest (ROIs: Fp2, F4, F8) during eyes-closed rest, controlling for demographics, physiological covariates (heart rate, HRV, BMI), and medication (CPZ equivalents).
   • Exploratory Analyses: Included subscale analyses, spatio-temporal cluster-based permutation tests for HEPs across all conditions, and Partial Least Squares (PLS) regression to examine multivariate brain-body-symptom associations.

Key Results

• Subjective Interoception: Individuals with SSD reported significantly altered interoceptive awareness compared to HC. Specifically, they exhibited reduced conscious interoceptive body awareness (lower MAIA total scores) and significantly elevated depersonalization (higher CDS scores). Notably, while global BPQ scores were comparable, SSD participants showed specific impairments in regulatory and emotional facets of interoception (e.g., "Not Worrying," "Attention Regulation") and heightened awareness of supra-diaphragmatic autonomic sensations.
• Behavioral Accuracy: In the preregistered model with extensive covariates, the group difference in interoceptive accuracy (HCT) showed a non-significant trend toward lower accuracy in SSD ($p=0.058$). However, a sensitivity analysis using a more parsimonious model revealed a statistically significant reduction in interoceptive accuracy for the SSD group ($p=0.0003$).
• Neural Processing (HEP):
  • Resting State: The study failed to replicate previous findings of increased HEP amplitudes in right-frontal ROIs during eyes-closed rest. No significant group differences were observed in the preregistered ROIs after covariate adjustment.
  • Context-Dependent Effects: Exploratory spatio-temporal analyses revealed that HEP alterations were highly context-dependent. During the active HCT, SSD participants showed significantly reduced HEP positivity (attenuated amplitudes) over centro-parietal regions (0.30–0.55 s post-R-peak). A similar, though weaker, attenuation was observed during eyes-open rest. No significant differences were found during eyes-closed rest.
• Clinical Correlations: Global symptom severity (PANSS total) showed a robust positive association with depersonalization (CDS). However, no significant correlations were found between global symptom severity and interoceptive accuracy, HEP amplitudes, or other self-report measures after correction. Exploratory multivariate analyses suggested directionally consistent but non-significant links between negative symptoms and a profile of increased depersonalization, heightened supra-diaphragmatic reactivity, and reduced trust in bodily sensations.

Significance and Claims
The authors claim that their findings provide multimodal evidence that interoceptive disturbances in SSD are pervasive but expressed differentially across domains. The study concludes that:

1. Disorder-Central Alteration: Interoceptive dysfunction in SSD is a disorder-central feature, most robustly expressed at the subjective level, characterized by impaired regulation and negative bodily appraisal alongside elevated depersonalization.
2. Context-Dependence: Neural alterations (HEP attenuation) are not fixed resting-state abnormalities but are context-dependent, emerging most clearly during active interoceptive engagement (HCT) and less so during passive rest. This suggests a deficit in the precision weighting of visceral signals when inferential demands are high.
3. Trait vs. State: The weak association between interoceptive measures and global symptom severity (outside of depersonalization) suggests that these alterations may reflect trait-like vulnerabilities rather than state markers of current symptom severity.
4. Clinical Relevance: The strong link between depersonalization and symptom severity highlights bodily self-disturbance as a central clinical correlate. The authors propose that interventions targeting interoceptive regulation (e.g., exercise, body-based therapies) may offer a promising avenue for improving brain-body integration in SSD.

The paper maintains a modest tone, acknowledging limitations such as the cross-sectional design, the specific cardiac focus of the measures, and the need for replication of exploratory multivariate findings in larger samples. It does not claim to have identified a definitive biomarker for SSD but rather characterizes the profile of interoceptive dysfunction across subjective, behavioral, and neural levels.