Social Smiling and Laughter Are Linked to Enhanced Functional Brain Connectivity in Young Infants' Default Mode
Olivia Allison1, Caroline Kelsey2,3, Tobias Grossmann1
1Department of Psychology, University of Virginia, Charlottesville, Virginia, USA.
Developmental Psychobiology
|September 26, 2025
Summary
Infant brain connectivity in the Default-Mode Network (DMN) was explored using functional near-infrared spectroscopy (fNIRS). While overall social engagement didn't link to DMN connectivity, infant smiling and laughter positively predicted left-hemisphere DMN connectivity.
Area of Science:
- Neuroscience
- Developmental Psychology
- Cognitive Science
Background:
- The Default-Mode Network (DMN) is crucial for social and cognitive functions.
- Understanding early DMN development and its relation to social behavior is vital.
- Individual differences in infant social engagement are linked to brain development.
Purpose of the Study:
- To investigate the relationship between positive social engagement and DMN functional connectivity in 5-month-old infants.
- To explore hemispheric differences in DMN functional connectivity.
- To determine if specific social behaviors predict DMN connectivity.
Main Methods:
- Functional near-infrared spectroscopy (fNIRS) was used to measure brain activity.
- 109 infants were initially recruited, with 35 in the final sample.
- Preregistered measures of positive social engagement were assessed.
Main Results:
- Infants showed greater DMN functional connectivity in the right hemisphere compared to the left.
- No significant association was found between preregistered social engagement measures and DMN connectivity.
- Infants' smiling and laughter positively predicted left-hemisphere DMN functional connectivity.
Conclusions:
- DMN functional connectivity in infancy shows hemispheric asymmetry.
- Specific positive social behaviors, like smiling and laughter, are associated with left-hemisphere DMN connectivity.
- Early social interactions may play a role in shaping long-range brain network development.
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