A new study published in the Journal of Psychiatric Research found a significant association between the neuropeptide oxytocin and social cognition in individuals with schizophrenia and healthy controls. This finding highlights the importance of endogenous oxytocin levels as a biological predictor of social cognition, regardless of clinical status.
In the study, investigators focused on assessing whether plasma oxytocin levels were associated with performance on a higher-order social cognition measure (for example, a task that requires inferential processes and knowledge not directly presented in social stimuli), as well as domains of general cognition. They recruited 30 individuals with schizophrenia and 21 healthy controls. The participants completed a clinical interview and were rated on the Brief Negative Symptom Scale, Brief Psychiatric Rating Scale, and Level of Function Scale. The MATRICS Consensus Cognitive Battery (MCCB) was administered to assess neuropsychological impairment concerning 7 domains:
- processing speed,
- working memory,
- verbal learning,
- visual learning,
- reasoning/problem solving, and
- social cognition.
Plasma oxytocin levels were measured via radioimmunoassay. One-way analysis of variance was used to examine group differences in plasma oxytocin levels, multivariate analysis of variance was used to evaluate group differences in the 7 MCCB domain scores, and Pearson correlations were used to evaluate associations between plasma oxytocin levels and the 7 MCCB domain scores in each group.
The investigators found that the group with schizophrenia had significantly lower endogenous oxytocin levels and poorer MCCB performance on all 7 domains than the control group. In both groups, lower endogenous oxytocin was associated with poorer social cognition. Among the participants with schizophrenia, lower endogenous oxytocin was also associated with poorer processing speed and working memory. Chlorpromazine equivalent dosage was not significantly associated with oxytocin levels or MCCB performance in the group with schizophrenia.
The study limitations include small sample size, male dominance, and the use of antipsychotics (chlorpromazine), which could have a moderating effect on the association reported. Smoking status was not reported, which might affect endogenous oxytocin levels, and the use of drugs was not tested the day of the study. Moreover, only a single measure of social cognition was used, limiting the results to the Mayer-Salovey-Caruso Emotional Intelligence Test subtest in the MCCB. Finally, plasma oxytocin levels reflect peripheral rather than central nervous system concentration, and oxytocin receptor density was not measured.
The study investigators concluded that significant associations between plasma oxytocin and general neurocognition might reflect either an anxiolytic effect of plasma oxytocin that results in better neurocognitive performance or oxytocin’s action on dopamine and enhancement of dopamine tone that results in improved cognition. These findings have important implications for studies administering exogenous oxytocin as a treatment for social cognitive deficits in schizophrenia.
Strauss GP, Chapman HC, Keller WR, et al. Endogenous oxytocin levels are associated with impaired social cognition and neurocognition in schizophrenia [published online February 17, 2019]. J Psychiatr Res. doi: 10.1016/j.jpsychires.2019.02.017