Interoceptive accuracy in patients with schizophrenia was significantly lower than that of healthy participants in a study recently published online in Schizophrenia Bulletin Open. As it was associated with both positive and negative symptoms of the disease, interoception in patients with schizophrenia could be a new therapeutic target, the researchers said.
Researchers measured interoceptive accuracy, which they defined as “an objective measurement” using a heartbeat counting task, and interoceptive sensibility, which they defined as “a subjective measurement” using a questionnaire, of 42 patients (21 males and 21 females, aged 40.5 ± 9.9 years, 12 inpatients) in Japan who had chronic schizophrenia and were taking antipsychotics (719.6 ± 487.9 mg chlorpromazine equivalent) and clinically stable at the time of testing, according to the Beck Depression Index-Ⅱ (BDI), the State Trait Anxiety Inventory (STAI), the Positive and Negative Syndrome Scale (PANSS), and the Global Assessment of Functioning score (GAF).
They compared their results with 30 healthy volunteers (aged 40.1 ± 9.9 years, 13 males and 17 females) who did not have neuropsychiatric disorders or any first-degree relatives with these disorders. The controls were matched with patients for age (P =.787) and gender (P =.637).
The education level was higher for the healthy controls (16.9 years ± 6.6 years) compared with the patients with schizophrenia (12.8 years ± 2.3 years, P <.001) and depression (BDI: 15.8 ± 11.0 for the schizophrenia group and 9.2 ± 7.4 for the healthy control group) and anxiety (STAI-trait: 48.2 ± 14.5 for the schizophrenia group and 43.4 ± 11.6 for the healthy control group; STAI-state: 46.8 ± 14.2 for the schizophrenia group and 40.6 ± 9.4 for the healthy control group) were more frequent in the schizophrenia group compared with the healthy controls (P < .001 in BDI, P =.028 in STAI-train, and P =.016 in STAI-state). Patients who had a major brain anomaly or organic brain disease, current substance abuse or learning difficulties were excluded from the study.
The researchers asked the participants to perform a heartbeat counting task and a time estimation task, which was used as a control task.
In the heartbeat counting task, participants counted and reported the number of times they felt their own heartbeat during the measurement period (2 runs of 25 seconds, 35 seconds, and 45 seconds for a total of 6 trials), and those numbers were compared to the electrocardiogram’s measurements.
In the time estimation task, participants counted and reported the number of seconds during each measurement period (2 runs of 23 seconds, 40 seconds, and 56 seconds for a total of 6 trials), and those numbers were compared to a stopwatch’s measurements.
The researchers used the Multidimensional Assessment of Interoceptive Awareness (MAIA), a questionnaire including 8 scales of interoceptive sensitivity: noticing, not-distracting, not-worrying, attention regulation, emotional awareness, self-regulation, body listening, and trusting. Higher scores in each assessment referred to superior interoceptive sensibility.
The researchers conducted a t-test to analyze the normally distributed data and a chi-square test to analyze categorical data for differences between the groups in characteristics, interoceptive accuracy and the MAIA score. They also performed a Pearson or Spearman correlation analysis between the HR-adjusted interoceptive accuracy and the participants’ PANSS scores.
The study authors found that the patients with schizophrenia had significantly poorer interoceptive accuracy (.32 ± .34 in the schizophrenia group, .68 ± .25 in the healthy control group, P < .001) and time accuracy (.73 ± .22 in the schizophrenia group, .84 ± .12 in the healthy control group, P =.006). There was a significant difference in interoceptive accuracy (P =.017) even after controlling for age, sex, time accuracy, BDI, STAI-trait, educational level, and heart rate, they said.
Heart rate-adjusted interoceptive accuracy of the group with schizophrenia was correlated with PANSS-P, PANSS-N and PANSS-G (rho (r) =-.420, P =.006 / r = -.442, P =.003 / r = -.469, P =.002). Subscales P2 (conceptual disorganization, P =.005), P3 (hallucination, P = .006), N1 (blunted effect, P =.006), N2 (emotional withdrawal, P =.003), N4 (apathetic social withdrawal, P =.001) and G16 (active social avoidance, P < .001) survived after Bonferroni-correction.
The researchers found that HR-adjusted interoceptive accuracy in schizophrenia was not correlated with the dosage of antipsychotic drugs (P =.225) and time accuracy was not correlated with PANSS-P, PANSS-N or PANSS-G (P =.544, P =.340, P =.293).
The noticing score in the MAIA questionnaire was significantly higher among the schizophrenia group (2.9 ± 1.2) than the healthy control group (2.2 ± .9, P =.005), while the score for not-distracting displayed an inverse pattern (schizophrenia group: 2.1 ± 1.2, control group: 3.0 ± .9, P =.001), but these scores were not associated with PANSS-P, N, or G (P =.424, .484, and .339 for noticing, P =.160, .945, and .195 for not-distracting).
The discrepancy between subjective (based on the score of noticing) and objective measurements was significantly correlated with PANSS-P (r = .419, P =.006) and PANSS-G (r =.417, P =.006), but not PANSS-N (P =.087). Subscales P1 (delusions, P =.003), P2 (conceptual disorganization, P =.007) and G16 (active social avoidance, P =.001) survived after Bonferroni-correction.
Limitations of the study included lack of conclusion on what parameter the interoceptive accuracy in the heartbeat detection task represents and since all patients were well treated for chronic schizophrenia, a longitudinal study would clarify the role of interoception depending on schizophrenic phase, PANSS may not be a suitable tool for assessing symptoms of altered bodily experience (such as depersonalization), the effect of antipsychotic drugs cannot be denied and since the study was a cross-sectional study, it is limited in its ability to provide evidence on causality.
“Negative symptoms were characterized by diminished emotional expression and avolition. To our knowledge, this is the first report to reveal the link between poor interoception and negative symptoms associated with schizophrenia,” the researchers said. “Interoception contributes to the development of emotion and volition, and poor interoception in patients with schizophrenia could result in their diminished emotional expression and avolition.”
Koreki A, Funayama M, Terasawa Y, Onaya M, Mimura M. Aberrant interoceptive accuracy in patients with schizophrenia performing a heartbeat counting task. Schizophr Bull Open. Published online November 27, 2020. doi:10.1093/schizbullopen/sgaa067