In animal social systems, the care of offspring can occur either through independent breeding, involving only the parents, or through cooperative breeding, where the infants receive care from multiple individuals.
Early brain development in primates is influenced strongly by social interactions. Callithrix jacchus, or common marmosets, like humans, are cooperatively breeding primates and share numerous life history traits with us.
In a recent study published in Science Advances, European researchers used neural tracing, neuroimaging, and behavioral assessments to examine how brain development in marmosets is influenced by social interactions and experiences, shedding light on the evolution of human social cognition.
Study: Neurodevelopmental timing and socio-cognitive development in a prosocial cooperatively breeding primate (Callithrix jacchus). Image Credit: Danny Ye/Shutterstock.com
Background
Social cognition and prosocial behaviors in humans are shaped by extensive allomaternal care provided by a non-maternal caregiver. Unlike the non-human great apes, humans are surrounded by caregivers who provide strong social interactions that are essential for developing emotional, social, and communicative abilities.
Primatological and neuroscience research has reported that the timing of social input and brain development plays a crucial role in social cognition. Accelerated brain development in the early stages has been linked to neurocognitive issues such as autism, affecting social behavior and cognition.
Studying other primates that are cooperative breeders, such as common marmosets, who also undergo extended post-natal brain development and allomaternal care, could provide valuable insights into the evolution of social cognition and prosociality, where species engage in behaviors that are beneficial for others.
About the Study
The researchers investigated how the timing of brain development in marmosets aligned with key social interactions during infancy and early development. They used a combination of behavioral assessments, connectivity analyses, and neuroimaging to create a detailed view of brain maturation in relation to social behavior.
In a cohort of about 40 marmosets aged 13 to 104 weeks, the researchers used structural magnetic resonance imaging (MRI) data to track the development of gray matter volume across 16 subcortical nuclei and 53 cortical areas. Using this data, the researchers observed the age-specific changes in the brain regions involved in social cognition.
Additionally, the study used functional MRI to identify the brain regions that are activated during the observation of social interactions. Data from previous studies were used to determine the areas that responded strongly when marmosets watched others of their species engage in social activity.
This also helped distinguish the areas that respond to social cues from those that were activated by non-social activities. These activation patterns were then mapped onto the developmental trajectories of social interaction.
Apart from imaging data, the researchers also gathered longitudinal data on behaviors during interactions involving food sharing within five family groups of marmosets, which included 14 young marmosets between the ages of one and 60 weeks, as well as 26 adults.
These behavioral observations provided them with insights into how infants interact with various caregivers over food and engage in begging behavior, which was a significant social interaction in the early life stages.
Furthermore, connectivity data at the cellular-level resolution was obtained by injecting retrograde tracers into the cortices of young-adult marmosets, and this data provided detailed information on the cortico-cortical connectivity or communication between neurons in different cortical areas. The connectivity data was used to determine structural connections among the brain regions involved in social cognition.
Major Findings
The study revealed that the regions in the marmoset brain that get activated after observing social interactions showed unique developmental patterns. These regions maintained their maximum gray matter volume for longer periods than the other regions, indicating that the plasticity of the brain in processing social interactions was sustained.
The basolateral amygdala, which is vital for processing emotional stimuli, and regions in the prefrontal cortex that are involved in social cognition exhibited the longest periods of gray matter plasticity.
The results indicated that in marmosets, the gray matter volumes decline faster in the areas involved in primary sensory responses but slower in the regions that process social interactions, similar to what has been observed in humans.
Furthermore, the brain development timelines are aligned with the social interaction stages, such as food-begging behavior. Infant begging is believed to be a complex social behavior that peaks at around 27 weeks and persists through young adulthood as an important social skill.
The study showed that the alignment of milestones in brain maturation and social interactions supported the role of social stimuli in the development of specific brain regions linked to prosocial skills.
Additionally, the researchers found that facial expressions were an important factor in infant-caregiver interactions among marmosets and allowed them to tune their social interaction processing skills finely.
Conclusions
Overall, the findings suggested that prolonged brain plasticity due to a slower decline of gray matter volume in the brain regions processing social stimuli supported the development of prosocial behavior in marmosets.
These patterns are similar to the social developmental stages observed in humans and highlight the importance of marmosets as an ideal model system for studying the evolution of social cognition in cooperative breeders.
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