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The prefrontal cortex is positioned at the frontal lobe of the brain. It is the most evolved part of the brain, associated with the highest cognitive abilities including, personality development and planning. It receives information from different brain regions, processes it, and acclimates accordingly (Ford & Kensinger, 2019). Moreover, it contributes to several executive functionalities including, executive processing, attention focusing, language processing, the anticipation of events, impulse control, and behavioral adjustment. However, it is highly susceptible to internal and external factors, which can influence its functional behaviors. For example, overwhelming stress results in loss of cognitive abilities, and continued exposure can cause architectural alterations in prefrontal dendrites.
The prefrontal cortex responds to stressful conditions in different ways. For instance, it shuts down stress responses when the subject can manipulate the stressor. However, the inability to control the stressor can reduce the prefrontal cortex’s capacity to regulate stress responses. It plays a significant role in the top-down management of behaviors, which is crucial in mental representation. The mental representation is required for malleable goal-oriented behavior such as managing arousal state by projecting noradrenergic neurons that manage locus coeruleus firing. In addition, most noradrenergic neurons are positioned within the locus coeruleus.
They also have projections all over the cerebral cortex and subcortical areas, including the amygdala, thalamus, and hippocampus (Borodovotsyna et al., 2018). Exposure to stress escalates firing in the locus coeruleus leading to increased release of norepinephrine. The increased firing results in the manifestation of certain behaviors such as fear. Exposure to chronic stress can cause long-term changes in locus coeruleus firing and release of norepinephrine. This hinders the prefrontal cortex’s ability to perform executive processing.
Exposure to stress noticeably weakens the effectiveness of the prefrontal cortex while stimulating more primitive responses of the amygdala and rapid firing of noradrenergic. The prefrontal cortex has extensive connections to brain parts and can heighten or even impede their actions. However, the amygdala initiates and coordinates an insentient stress response throughout the body and the brain during stressful conditions (Ford & Kensinger, 2019). It activates the hypothalamus-pituitary-adrenal gland through the projection to the hypothalamus, which releases adrenaline needed for flight or fight responses. This results in a quick change of a subject’s behaviors, for example, prompting the freezing reaction by activating the periaqueductal gray.
The main role of periaqueductal gray is the dictation of pain and responding with the appropriate behavior. Intriguingly, it is associated with assessing risk and reacting to the threats through defensive behaviors. It has two main descending pathways: the ventromedial medulla and the locus coeruleus (Brandao & Lovick, 2019). The locus coeruleus path transmits by norepinephrine, applying an ant-nociceptive effect upon the dorsal horn by stimulating alpha-2 receptors. This decreases the dorsolateral prefrontal cortex neurons firing, leading to loss of impulse control.
Acute stress weakens the prefrontal cortex functions on the working memory. The working memory has a system for sustaining, monitoring, and controlling information in short-term memory while connecting to long-term memory. However, exposure to stress weakens dorsolateral prefrontal cortex network connections. This is due to high levels of dopamine and norepinephrine that weaken close-by synaptic connections (Marttunen et al., 2020).
The dopamine levels cause changes in the mesolimbic dopamine system, which are crucial in coping with stress by tolerating adjustments to different environmental stimuli. Under stressful conditions, the dopaminergic reward system assesses situations and picks the optimal processing for dealing with the circumstance. Increased dopamine levels stimulate D1 receptors present in the prefrontal cortex impairing working memory.
Norepinephrine is released under stressful conditions, and its levels dictate the molecular switch, which determines whether the prefrontal cortex is engaged or impaired. Normal norepinephrine levels in non-stress environments engage alpha-2A receptors, reinforcing prefrontal functions (Marttunen et al., 2020). Furthermore, the stimulation of Alpha 2A receptors prevents cAMP signaling that closes potassium channels. This results in the strengthening of connectivity, thus allowing neural firing, which increases top-down behavioral control. In contrast, however, its high levels heighten the adrenoceptor, leading to potassium channels’ opening. This prevents neuron firing, hence hindering the working memory.
On the other hand, catecholamines in their high levels strengthen amygdala responses, which are more primitive. The amygdala plays a significant role in examining and reacting to environmental risk by assessing the emotional significance of the sensory information and provoking a suitable response. It has connections to brain regions that process higher cognitive and lower control functions. This enables it to control physiological responses based on the cognitive information available (Ford & Kensinger, 2019). There are feedforward interactions that are crucial in maintaining the desired fundamental state of the brain.
Under non-stress conditions, moderate catecholamine’s released, which engages high-affinity alpha 2A receptor, thus weakening the amygdala and regulating locus coeruleus neural firing. However, excessive stress activates the primitive circuits increasing the release of catecholamine. This causes activation on alpha one receptors that take the prefrontal cortex offline thus, reducing control of the amygdala, brainstem, and striatum. Hence, overwhelming emotions can result in illogical responses when faced with danger.
References
Borodovotsyna, O. Flamini, M. & Chandler, D. (2018). Acute stress persistently alters locus coeruleus function and anxiety-like behavior in adolescent rats. Neuroscience, 1(2), 7-19.
Brandao, M. & Lovick, T. (2019). Role of the dorsal periaqueductal gray in posttraumatic stress disorder: mediation by dopamine and neurokinin. Translational psychiatry, 9 (232), 508-516.
Ford, H. & Kensinger, E. (2019). The role of the amygdala in emotional experience during retrieval of personal memories. Memory, 27(10), 1362-1370.
Marttunen, V. Andreassen, O. & Espeseth, T. (2020). Neuroscience & biobehavioral reviews. Science direct, 118, (20), 298-314.
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