Maternal immune activation alters bout structure of rat 50-kHz ultrasonic vocalizations

Dysfunctional sequencing of behaviour and cognition is observed in schizophrenia across multiple domains, including during communication. We examined whether maternal immune activation (MIA), a risk factor for schizophrenia, disrupted the sequential organization of ultrasonic vocalizations (USVs) in a rat model. We analysed the structure of bursts of 50-kHz USVs (bouts) in two independent datasets (paired-rat: 19 control, 18 MIA; reward paradigm: 18 control, 20 MIA), using a Damerau-Levenshtein analysis with a k-fold cross-validation procedure. MIA animals showed greater variability in their bout sequences in both datasets, with lower Levenshtein similarity index (LSI) scores compared to control animals. Notably, MIA set median sequences were more similar to control bout sequences than to their own group's sequences, suggesting a breakdown in sequential organization. Additionally, we found an alteration to 50-kHz USV transitional preferences in MIA in a reward context. While sequence structure was altered, basic call production and call-type distribution remained largely intact across groups. These findings demonstrate that MIA specifically appears to affect the organization of vocal sequences at the bout level, while largely preserving basic vocalization patterns. This work extends our understanding of the effects of maternal infection during pregnancy, and how this can lead to altered communication sequences that are relevant to schizophrenia risk.