In the darkness of the womb, a silent conversation takes place between the mother and fetus. Encapsulated in biochemical signals, quiet pulses of sadness and fleeting moments of calm guide the architecture of the baby’s amygdala. Emerging research suggests that our emotional state and predisposition to mood disorders come not only from our postnatal environment, but also from our prenatal one. The brain fine-tunes itself in anticipation of the external world. The result? An altered balance in regulating stress and fear responses. 

Approximately 10-15% of U.S. women experience a major depressive episode during pregnancy, and 16% of women experience clinical anxiety. One of the areas involved in mood disorders is the amygdala. Nestled in our limbic system, this small almond-like structure is responsible for threat detection, assigning emotional significance to experiences, and regulating stress responses. Given its crucial role in emotional processing, researchers seeking to understand neurobehavioral development have begun to investigate how prenatal (before/during pregnancy) influences like maternal stress and depression shape this region. 

Emerging research studies have concluded that the prenatal environment affects axonal organization, fundamentally altering the structure of the amygdala in newborns—specifically, the right amygdala. So, what does this mean? 

Our brains are made up of neurons, which are specialized cells that enable communication with the brain and nervous system. On these neurons are axons, which are long, thread-like fibers that connect and transmit information by sending and receiving electrical and chemical signals. This vast network helps us to react to both our environment and regulate our internal state. Maternal depression and stress result in weaker/fewer axonal connections in the amygdala, which means less communication between surrounding brain regions.

Maternal depression's effects on cortisol compound the effect of a decreased number of axons. An increased and/or prolonged production of cortisol during fetal development renders oligodendrocytes, the cells that create myelin sheets, less effective. Myelin, a fatty insulation around axons, facilitates faster communication between cells. With fewer axons in place, in addition to slower communication, this can result in impaired emotional regulation.

Alterations in the amygdala’s connectivity result in a possible endophenotype for future emotional dysregulation/mood disorders. Endophenotypes are hidden clues linking our genes to our thoughts, feelings, or behavior. It’s crucial for scientists to study and understand these traits to create a robust understanding of emotional and cognitive development. This is particularly significant when considering that brain structures work in tandem with surrounding structures. The dorsolateral prefrontal cortex (dlPFC) plays a crucial role in healthy emotional regulation, and scientists have discovered an inverse functional connectivity between the amygdala and the dlPFC. Therefore, there is a higher likelihood of the amygdala remaining overactive while the dlPFC decreases in reactivity, failing to regulate the amygdala effectively.

Additionally, scientists have found high concentrations of white matter (axons) in other parts of the limbic system, like the hippocampus, the amygdala’s neural neighbor. The hippocampus is where short-term memories are converted to long-term ones, and its proximity to the amygdala allows emotions to become deeply intertwined with our experiences. Prenatal stress and depression cause increased synchronized activity between these two brain regions, thus disrupting the delicate balance of regulating stress.

There has yet to be an extended study on the long-term effects of adverse experiences during the prenatal period; however, it is hypothesized that the development of the amygdala and its surrounding structure is meant to prepare the fetus for a hostile outer environment.

Though we inherit certain neural scripts, the beauty of the human experience is that we have the tremendous potential to transform. As we carry our quiet beginnings, evidence-based therapeutic interventions like cognitive behavioral therapy (CBT) give us a space to bring them forth. The amalgamation of our experiences, both prenatal and postnatal, might run deep, but we are not resistant to change. We were designed to adapt, survive, and overcome.