A neuroimaging study involving participants from the fetal period up into the first four years of life found that the volume of the amygdala region of the brain increases with age and that this increase is steeper in boys than in girls. The paper was published in Human Brain Mapping.
The amygdala is a small, almond-shaped structure located deep within the brain’s temporal lobes. It is best known for its role in processing emotionally significant information. The amygdala is particularly involved in detecting potential threats and coordinating responses to fear, although its functions extend well beyond negative emotions.
The amygdala helps the brain determine which events are important and therefore deserve attention or should be remembered. It interacts closely with regions involved in memory, decision-making, and physiological stress responses, including the hippocampus and prefrontal cortex. Through these connections, it can influence changes in heart rate, hormone release, vigilance, and behavior when a person encounters something emotionally meaningful.
The amygdala also contributes to learning associations between particular situations and positive or negative outcomes. It participates in a broader neural network that evaluates the relevance and motivational significance of experiences.
Study author Megan E. Mueller and her colleagues investigated the development of the amygdala during late fetal, newborn, and early childhood periods—timeframes for which there has not been much published data so far. They also examined the links between amygdala development and specific aspects of psychological development for those participants for whom this data was available.
They analyzed data from cross-sectional (looking at different children at one specific point in time) and longitudinal (following the same children over a period of time) studies collected at Western University (Ontario, Canada) and from three open-access datasets. Data came from 11 unique participants of the Alberta Pregnancy Outcomes and Nutrition Study (APrON), from 30 participants of the CMIND study, 348 participants from the Developing Human Connectome Project, and from three more groups collected at Western University involving a total of 82 participants (Fetal Cohort 1, Fetal Cohort 2, and the Infant Cohort).
In total, these datasets contained data from 471 unique participants. Across datasets, females comprised 47% of participants. The age of participating children ranged between 27 weeks postmenstrual age (measured from the mother’s last menstrual period, representing the fetal stage) to 195 weeks postmenstrual age (around 3 years postnatal age) at the time of neuroimaging.
For 30 participants from the CMIND dataset, data on neurodevelopmental abilities, collected using the Bayley Scales of Infant and Toddler Development, Third Edition, were also available. These included assessments of cognitive, language, motor, social-emotional, and general adaptive abilities (practical, everyday life skills).
Results showed that the volume of the amygdala increases with age and that this age-related change is steeper in boys than in girls. Also, male participants tended to have larger amygdalae overall. The amygdala on the left side of the brain was larger and showed a steeper age-related increase than the right side.
When study authors looked at the 30 participants for whom neurodevelopmental data were available, they found that participants with smaller left amygdala volumes tended to have somewhat better social-emotional outcomes, cognitive outcomes, and better receptive communication (the ability to understand spoken language).
“We found that sex, laterality [differences between the left and right sides of the brain], and age predicted the volumes of the amygdala in a typically developing sample [children without neurodevelopmental disorders], providing a more thorough understanding of its development in the fetus and throughout infancy,” the study authors concluded.
“Additionally, identifying the impact of the development of the left amygdala on later communication, cognitive and social outcomes in toddlerhood provides further evidence that biological differences may be predictive of later prosocial or adverse outcomes, even in typically developing populations.”
The study contributes to scientific knowledge about the development of the brain. However, the associations with developmental outcomes were calculated only on data from a single dataset that included a very small number of children and infants. Because of this, the study authors suggest that these associations should be treated as preliminary.
The paper, “Age-Related Changes in the Amygdala From In Utero to Early Childhood: Association With Social and Cognitive Outcomes,” was authored by Megan E. Mueller, Emily S. Nichols, Sarah Al-Saoud, Barb de Vrijer, Charles A. McKenzie, Roy Eagleson, Sandrine de Ribaupierre, and Emma G. Duerden.