The Effects of Stress on Brain Development: Analysis of Results

This study aims to explore the effects of stressors on the development of the human brain. The effects of stress are very important to consider as it impacts individuals’ lives everyday and can affect their physical health too. Stress is commonly known as one of the factors that affects the brain development of humans everyday and can cause irreversible effects. In order to fully explore the effects of stress on brain development, numerous literature articles were studied and taken into consideration all together. The studies concluded that stress or stressors can lead to negative impacts on neonatal cerebral cortex 5-hydroxytryptamine synthesis mechanism, working memory,amygdala, and grey matter region of the human brain. Maternal stress directly impacts the neonatal 5-hydroxytryptamine and fetal brain as an increase in maternal plasma free tryptophan is directly correlated with fetal brain tryptophan levels and 5-hydroxytryptamine. Volume of grey matter region in brain decreases and stressor increases. The working memory decreases as chronic stress increases. Lastly, amygdala increased in volume due to stressful deprivations and its function is negatively impacted. These results and effects of stress in overall on brain development is discussed thoroughly the essay. 

Introduction

Brain development is a heavily complex procedure and can it can be influenced by the demands and challenges of the environment. Such demands can impact the structure and the function of the brain. The organ brain itself is composed of neural circuits that is structured based on physical needs and the ongoing experiences, which enables the brain to restructure. Stress is one of the factors that affects the brain development of children. In 1994, Wegner based his theory of mental control on the fact that people want to control their mental activities by suppressing unwanted thought. These unwanted thoughts include, but not limited to, negative emotion, losses and stressful events like poverty, which leads to stress. In recent studies, differences in life stress have also been found to be linked to differences in information processing. These unwanted thoughts, also referred as off-topic thoughts, could scarcely be characterized as stress-related.

Although the exact mechanism is unknown, many researchers have studied possible mechanisms in regards to how stress can influence brain development. Stressors stimulates the sympathetic nervous system and the hypothalamic-pituitary adrenal (HPA) axis. Prolonged activation of these due to chronic levels of stress can lead to abnormal reactivity of the HPA axis. As the stressor is stimulated, corticotropin-releasing hormone and arginine vasopressin are released and they reach adrenocorticotropic hormone, which is located in the anterior pituitary. The adrenocorticotropic hormone helps release the glucocorticoid receptors. In an review-journal article by the Emory University School of Medicine, a study by Heim et. al in 1997 concluded that an increase in corticotropin-release factor (CRF) activity shows consistency with the numerous symptoms of anxiety or PTSD.

In relation to developing brain, stress can drastically affect a human’s biology and behavior through early experiences. Stress is also one of the elements that not only has severe impacts but can also cause severe disorders, an example being post-traumatic stress disorder. Brain views stress as a threat and compensates for it through physiological and behavioural changes. Such changes can be temporary or permanently damage regions of the human brain and its functions. One of the studies found that due to maternal depression, infants experience neurobiological changes and these effects can be long lasting. Stress that lasts for a prolonged time can lead to an increase in allostatic overload. Allostatic overload is defined as overuse or imbalance between the sympathetic nervous system, the parasympathetic nervous system, hypothalamic-pituitary-adrenal (HPA) axis, immune system and mechanisms for all organs, which includes the brain.

The purpose of this research paper is to study the effects of stress or stressors on human brain development. In order to examine this topic, various primary literature and reviewed journals are used. The effects of stress on brain receptors, grey matter regions of the human brain, and working memory will be thoroughly discussed.

Analysis of Results

Decrease in 5-HT in Cerebral Cortex

Maternal stress is the amount of stress a pregnant mother is exposed to. It is heavily influenced by environmental stimuli. Examining maternal stress effects is significant as it can have adverse effects on the fetus. A study by the University of Ottawa examined whether maternal stress can impact a neonatal cerebral cortex 5-hydroxytryptamine synthesis mechanism. The 5-hydroxytryptamine (5-HT) is commonly known as serotonin which through previous studies have shown its involvement in brain development and that stress can include tryptophan and 5-HT levels. Specifically, a study by Lauder et al. showed that through the 5-HT axons, the 5-HT cell itself has the ability to interact with other proliferating cells during late gestation to postnatal period, which is why was it was concluded that 5-HT may play a role in the development of less differentiated cells. In order to study this, daily saline injections were combined with a “stressor” ,which in this study is crowding, and was provided to maternal rats in their final week of pregnancy before birth. Specifically, previous studies including “Both Prenatal and postnatal factors contribute to the effects of maternal stress on offspring behaviour and central 5-hydroxytryptamine receptors in the rat” by Peters, have shown that maternal stress can successfully change the 5-HT receptor binding, which leads to the chemical molecules, agonists, being unable to bind to the 5-HT receptor and have the same intensity of behaviour responses that they would be produced otherwise. To study the effects of maternal stress on brain development, cerebral cortex was examined for each of the subjects within this study. Cerebral cortex was chosen because previous studies have shown that 5-HT levels were significantly higher in the cerebral cortex while other brain regions showed little to no change.

In this study Peter, maternal stress had little to no impact on offspring’s body and brain weights. As the stress-induced in plasma-free tryptophan increased, so did the fetal brain tryptophan and 5-HT. Moreover, the prenatal stress led to an increase in the 5-HT, tryptophan, and 5-HIAA in the cerebral cortex region of the brain. This shows that maternal stress mechanism includes maternal plasma free tryptophan. This is responsible for an increase in the fetal tryptophan, 5-HT and 5-hydroxyindoleacetic acid. If stressed-related synthesis of 5-hydroxytryptamine is high, which is responsible for controlling neuron development at the perinatal time, may play a role in the adult brain later on in life.

Grey Matter Region

In a study, poverty was defined as a stress and examined the results on children which also showed adverse effects. Such experiments and studies examine the specific effects of poverty on human brain development. Through various studies, it has been confirmed that toxic effects of stress can negatively impact an individual’s overall health throughout their lifespan. Another study examined children whose family dynamic was in poverty had a decrease in their frontal lobe grey matter volume, temporal lobe grey matter volume, and the hippocampus grey matter volume. Grey matter is located within the brain, specifically the central nervous system, and it is made up of neurons which is responsible for creating nerve impulses. Overall, it is responsible for motor activity,and receiving sensory information including touch, smell,memory, seeing and hearing. The location of grey matter within the brain regions including the hippocampus, frontal lobe and the temporal lobe. Magnetic Resonance Imaging (MRI) was used to scan the subjects’ brains for this study.

This collected data was then used to study the association between the decrease in grey matter volume, which was already found to be associated with stress, to the children’s academics aspect. Based on the results, grey matter volume for children belonging to families below 1.5 times the federal poverty level were 3 to 4 percentage points below the normal developmental grey matter volume. Through using the Wechsler Abbreviated Scale of Intelligence (WASI) and the Woodcock-Johnson III Tests of Achievement (WJ-III), the academic achievement was evaluated properly. Specifically, these test studied general knowledge, language and math aspect of academic performance. Based on these tests, children that fell in the federal-poverty line scored 4 to 7 points lower on their standardized tests compared to the control group. The longer children lived in poverty, the greater their academics achievement decreased. Overall, the study concluded that based on the collected evaluation, the frontal grey matter volume and the temporal grey matter volume was accounted for about 15% to 20% of income-related achievement gap. Another study that was conducted and examined similarly, also supports these results that children suffering from poverty had a lower frontal grey matter volume and a lower parietal grey matter volume.

Working Memory

Early stressful events like childhood poverty can later on affect the adult working memory of an individual. Working memory is a “temporary storage mechanism that enables human beings to retain a limited amount of information for a short period of time”. Working memory is responsible for temporary storage, translating stimulus through the auditory and visual channels. This temporary storage is required in order for information in the brain to be encoded into the long-term memory. Thus, it plays a very important role for such basic skills as problem solving, language and reading. Such side effects have been studied and researchers have led to a conclusion that chronic stress is detrimental to a human’s working memory. The study, “Childhood poverty,chronic stress, and young adult working memory; the protective role of self-regulatory capacity,'' examined the relationship between stress and working memory. Two hundred and forty one young adults who had exposure of childhood poverty in their early-life, were chosen to participate. The results of this research showed a direct correlation between chronic stress caused by poverty and the working memory. Specifically, children who grew up in poverty had an elevated level of chronic stress and detrimental working memory as young adults. Another study by Evans and Schamberg had similar results as it depicted childhood poverty is inversely related to working memory.

For one of the studies, college students were selected as participants and were given a ten question questionnaire called the State-Trait Personality Inventory, which was used to examine the subjects’ current anxiety at the time of the experiment. The Life Experiences Scale (LES) was used, a checklist that presents common stressful events, including death and job problems, to measure the overall stress of the subject’s lifespan. Lastly, the Turner and Engle’s 1989 arithmetic operation-word memory task was used, in which the participants read a simple arithmetic equation on the computer and verbalized whether the answer given to the problem was true or false. Based on the results collected, the amount of negative life stress had an inverse relationship with working memory. So, the amount of stressful events increases, the ability of working memory decreases.

Emotions Through Amygdala

Amygdala is responsible for storing memories that are based on emotions like fear, anger, happiness, and sadness. It is part of the limbic system, specifically it is located inside the temporal lobe. In an article by Pechtel & Pizzagali, it is stated that amygdala is present and reaches its maximum volume as early as the age of 4 in females. Therefore, it is known to be reactive in early age, compared to adulthood. Within this article, a study mentioned called “A review of adversity, the amygdala and the hippocampus: a consideration of developmental timing” concluded that children who were adopted late, were more influenced by emotional events, which played a role in them having difficulties in emotion regulation. Here, the late adoption was the stressor. Overall, this shows that amygdala was not able to function properly in regards to emotions aspect due to an environmental stressor. Another article examined a study by Lupien et. al. showed that children provided with poor maternal care showed an increase in amygdala volume in their brain region. Specifically, there was a direct correlation between the mean depressive score of the mother and the amygdala volume in children.

Conclusion

Based on the studies and reviewed-articles examined, stress is shown to have a negative impact on brain development. Stressors like poverty, maternal stress, and early life stress were studied in regards to their impact on the brain development. Based on the effects of stress on 5-HT, there was an increase in the 5-HT, tryptophan and 5-HIAA in the cerebral cortex region of the brain. An increase in stress-induced 5-HT synthesis in the fetal brain may impact in the alteration mechanism on adult behaviour. Another dynamic studied was the effects of poverty, a form of stressor, on the grey matter region of the brain and its impact on academic performance. Based on the studies, it is concluded that suffering from poverty causes a decrease in the frontal grey matter volume and the parietal grey matter volume. Moreover, the academic performance also deceases. Working memory, an important factor in encoding long-term memories ,showed that as the amount of stressful events increases, the ability of working memory decreases. Lastly, the effects of stress on amygdala, an integrative region of the brain, was studied and it is concluded that amygdala is unable to function properly regarding emotion regulation if early life stressful events occurred. Moreover, stress also leads to an increase in the amygdala region of the brain when children are exposed to derivatives.

This suggests the potential of amygdala volume being a biologically sensitive early marker for maternal care quality. Further studies in regards to effects of stress should be explored and examined thoroughly in areas of PTSD mechanism in the brain, effects of natural disasters stressors on mental health. Another study that can be studied is the effects of deficiency in sleep on early brain development.

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