Vocal behaviors are a key signal for animal communication. Communication assists organisms with mating tactics, creates signals about predators, and conveys who is dominant. While vocal communication seems fairly straightforward, it actually integrates physiology, behavior, movement, emotions, and environmental cues. The physiological functions involved with vocal behavior include heartbeat, breathing, and blood pressure. In Marmoset monkeys, rhythmic changes in autonomic nervous system activity, the “rest and digest” system, are a possible drive for vocal production.
Past studies have investigated the potential link between vital signs, such as heart rate and blood pressure, and vocalizations in marmosets. A study done by Risseuno-Segovia, Koç, Champéroux, and Hage (2022) monitored monkeys freely moving rather than monkeys that were handled to avoid stress. The handling could be a possible confound for physiological activity.
To look into physiological states and physiological responses and their respective association with vocalizations, wireless transmitters were implanted in the abdomen of each monkey. Heart rate, blood pressure, and physical activity were measured and sent to a nearby monitor. These behaviors and vocalizations were recorded with a microphone and video camera (Figure 1), from which various vocalizations were recorded, including barks, grunts, warbles, and screams.
Additionally, increases in fight-or-flight responses have been shown to be a measure of “rest and digest” activity, or autonomic activity from the nervous system. So, changes in activity of the autonomic nervous system should be reflected in the fight-or-flight responses, such as heart rate, respiratory amplitude, and respiratory rate. Increases in heart rate occur with increased vocal production, which could be explained by the vocal production having higher physical activity.
To eliminate the possibility of physical activity impacting heart rate, vocal production was divided into high, medium, and low physical activity groups and thus compared to the monkeys’ respective heart rate. This division revealed that an increased heart rate was indeed associated with vocal onset, regardless of the level of physical activity.
To eliminate another possible confound, that increases in heart rate could be linked with inspiratory activity in the respiratory cycle, the data was then compared to the respiratory amplitude. The inspiration amplitude is associated with the act of vocalizing, with a higher rate of inspiration before vocal onset and a decrease during vocal production.
Activity in the fight-or-flight region of the nervous system has been shown to precede vocal production during social interactions. Cardiac activity has a direct influence on vocal behavior as shown by blood pressure oscillations and heart rate. Increased cardiac activity and increases in activity of the fight-or-flight section of the nervous system are associated with reinforced vocal onset.
These results demonstrate that cardiorespiratory activity is correlated with vocal onsets to optimize arousal and minimize energy expenditure during vocal production. Without this increase in cardiorespiratory activity and without the way the cardiorespiratory system and the brain interact, there would be a large decrease in energy, as the systems responsible for vocal production and the systems responsible for cardiorespiratory activity are connected. The lungs and heart are necessary for vocal production, so if vocalizations and cardiorespiratory activity did not occur at the same time, these systems would be working twice as hard to produce these responses.
Citations:
Risueno-Segovia, C., Koç, O., Champéroux, P., & Hage, S. R. (2022). Cardiovascular mechanisms underlying vocal behavior in freely moving macaque monkeys. iScience, 25(1), 103688. https://doi.org/10.1016/j.isci.2021.103688
