Different forms of early-life stress may shape the development of brain areas involved with emotion processing and may increase vulnerability to adult mental or behavioral disorders. Examples of types of traumatic events include natural disasters, experiences in institutional care, assaults, witnessing violence and physical, sexual and emotional abuse.
Considering that exposure to stress in humans may entail a complex interaction among multiple factors, researchers can more easily monitor its effects and experimentally control its causes using animal models. A new study conducted by Coplan et al. investigated early-life stress in the bonnet macaque. Stress exposure was achieved in the offspring through imposing unpredictable foraging conditions on the mother. During this procedure, defined as variable foraging demand (VFD), food was more difficult to access and the quest prevented VDF mothers from adequately attending to their infants.
In their study, the researchers examined amygdala volume in VFD-reared and normally reared bonnet macaques. The amygdala is a set of neurons located in the brain’s medial temporal lobe. This brain structure plays a key role in the processing of emotions and is linked to both fear responses and pleasure. Conditions such as anxiety, post-traumatic stress disorder, depression and phobias are suspected of being linked to abnormal functioning of the amygdala, causing damage, developmental problems, or neurotransmitter imbalance. Several observations suggest that early life stress may alter amygdala volume. This biological modification seems to be moderated by the presence of polymorphisms in the serotonin transporter gene, therefore the correlation between its genotype and amygdala volume was also explored by the investigators.
The subjects underwent MRI scans and the images were imported into Analyze software and converted to cubic voxel dimensions using a cubic spline interpolation algorithm. The software was also used to isolate whole brain from its surroundings, manually trace the amygdalae and measure their volume.
VFD-reared macaques possessing the short allele of the serotonin transporter gene exhibited larger amygdala volume compared to unstressed controls with the short allele and individuals presenting the long allele. The results of this study also shed light on the relationship between the amygdala and other structures that are affected by early life stress. In fact, the same MRI scans revealed both reduced left hippocampal volume and smaller corpus callosum cross-sectional area in VFD subjects.
Findings from this study highlight the association between early life stress and biological changes that become evident across the lifecycle. Although future research aims to identify factors that may promote resilence to stress, society should always keep in mind that the experiences children are having are shaping the individuals these people will become.Corpus Callosum, Hippocampal Atrophy, Neurodevelopment, Stress