On the physiology of grooming in a pigtail macaque

Several functions of social grooming have been proposed, including building affiliative bonds between group members, and reducing tension or anxiety. In this case study, heart rate (HR) of a single adult female pigtail macaque living in a social group was monitored in several behavioral contexts to examine the relationship between grooming and HR level, an indicator of autonomic nervous system activity. The subject was implanted as a part of another study with a multichannel telemetry system which monitored several physiological variables. Physiological and behavioral data were collected over a nine day period. Heart rate during agonistic interactions was significantly higher than during other categories of behavior, and sleep HR significantly lower. When the subject received grooming from others, HR was significantly lower than during self grooming or initiating grooming to others, as well as during other behaviors. HR showed significant declines during bouts of receiving groom (up to 20 bpm), but not during bouts of initiating or self grooming. Following aggression, HR decline was greatest while receiving grooming. There were also HR differences for methods of grooming: stroking but not other methods related to decreases in HR.