This article examines the impact of stress on the brain, exploring the neurobiological mechanisms and psychological consequences of chronic stress. It discusses how the stress response, initiated by the activation of the amygdala, triggers a cascade of hormonal changes that affect the brain's structure and function. Special attention is given to the effects of stress on neuroplasticity, inflammatory processes in the brain, as well as cognitive and emotional consequences. The article also addresses gender differences in stress response and strategies to protect the brain from its adverse effects. The article emphasizes the importance of understanding these mechanisms to develop effective interventions aimed at improving psychological resilience and reducing the risk of mental disorders.

Keywords: stress, neurobiology, psychology, amygdala, hippocampus, neuroplasticity, cortisol, chronic stress, cognitive functions, emotional consequences, gender differences, mental disorders, neuroinflammation, psychological resilience.

Stress is not merely a subjective experience but a complex physiological response that profoundly affects the structure and function of the brain. Contemporary research in neurobiology and psychology demonstrates that chronic stress can modify neural networks, impact cognitive functions, and increase the risk of mental disorders. This article explores the key mechanisms through which stress transforms the brain, drawing on data from psychological and neurobiological studies.

Neurobiological Foundations of the Stress Response. The stress response begins with the activation of the amygdala, the brain region responsible for processing emotions, particularly fear and anxiety. Upon perceiving a threat, the amygdala sends signals to the hypothalamus, initiating a cascade of hormonal changes through the hypothalamic-pituitary-adrenal (HPA) axis. This cascade results in the release of cortisol and adrenaline, preparing the body for a «fight or flight» response. However, chronic activation of this system has detrimental effects. Research indicates that prolonged exposure to cortisol damages the hippocampus, a brain region critical for memory and learning. Individuals experiencing chronic stress exhibit a reduction in hippocampal volume, which correlates with impaired episodic memory and a diminished capacity to acquire new information [1; 6].

The stress response originates in the brain when threat information reaches the amygdala, a region involved in emotional processing. The amygdala interprets images and sounds, triggering a cascade of stress hormones that produce well-coordinated physiological changes. Stressful situations, whether environmental, such as an impending work deadline, or psychological, such as persistent worry about job loss, can trigger a cascade of stress hormones that induce physiological changes like increased heart rate and rapid breathing [2; 5].

Impact of Stress on Neuroplasticity. Neuroplasticity is the brain's ability to adapt to new experiences by forming and reorganizing synaptic connections. Chronic stress suppresses this process by reducing the production of brain-derived neurotrophic factor (BDNF), essential for neuron growth and survival. Experiments on animals demonstrate that stress leads to dendritic shrinkage in the prefrontal cortex, the area responsible for decision-making, impulse control, and emotional regulation. This explains why individuals under chronic stress often struggle with concentration, exhibit impulsive behavior, and experience emotional instability [2; 5].

Stress can also affect neuron function in the frontal lobes, which are crucial for attention, filtering irrelevant information, and using judgment to solve problems. Long-term stress can lead to «brain fog», a symptom also associated with many immune-related diseases. Researchers in psychoneuroimmunology study how the immune and nervous systems interact and influence people's mental and emotional health.

Stress and Inflammatory Processes in the Brain. One of the most significant recent discoveries is the link between chronic stress and neuroinflammation. Prolonged activation of the HPA axis leads to increased production of pro-inflammatory cytokines such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). These molecules can cross the blood-brain barrier and activate microglia, the brain's immune cells. Studies show that activated microglia begin to attack healthy neurons, exacerbating neural tissue damage. This process is associated with the development of depression, as patients with clinical depression exhibit elevated levels of inflammatory markers in the brain. Moreover, chronic inflammation can accelerate neurodegenerative processes, increasing the risk of diseases such as Alzheimer's [5; 4].

Chronic stress can have negative health consequences, including mood changes, weakened immune and digestive systems, and cardiovascular health deterioration. The central nervous system is responsible for the «fight or flight» response. In the brain, the hypothalamus signals the adrenal glands to release stress hormones such as adrenaline and cortisol.

Cognitive and Emotional Consequences. Stress radically changes how the brain processes information. Under the influence of cortisol, the activity of the prefrontal cortex decreases, impairing working memory, cognitive flexibility, and planning ability. In an experiment with mice subjected to chronic stress, the animals continued to use ineffective behavioral strategies even after the task conditions changed, demonstrating cognitive rigidity. The emotional sphere also undergoes significant changes. Stress enhances negative cognitive bias—the tendency to interpret ambiguous situations pessimistically. In a study where participants played an economic game, those under stress more often expected negative outcomes, even when objective data indicated an equal probability of success and failure [4].

Stress can cause physical, psychological, or behavioral symptoms. People with chronic stress often try to cope with it in various ways, some of which can be harmful to health. A primary care provider can help by offering advice, prescribing medication, or referring to a mental health professional such as a psychologist or psychiatrist [3].

Gender Differences in Stress Response. Interestingly, stress affects male and female brains differently. Women exhibit prolonged amygdala activation after stressful events and higher sensitivity to corticotropin-releasing hormone (CRH), which triggers the stress response. This may explain why women are more prone to anxiety disorders and depression. In an experiment with mice, females subjected to social stress displayed anxious behavior for 10 weeks, whereas males returned to normal within two weeks [3; 4].

Strategies to Protect the Brain from Stress. Despite the grim picture, the brain has a significant capacity for recovery. Regular physical activity stimulates neurogenesis in the hippocampus and increases BDNF levels. Meditation and mindfulness practices have been shown to increase gray matter volume in the prefrontal cortex and reduce amygdala density. Subjective perception of control also plays a crucial role. In a classic experiment, rats that could gnaw on a stick during an electric shock experienced significantly less stress compared to those without such an option. This demonstrates that even symbolic forms of control can mitigate the negative effects of stress [8].

Stress is a powerful factor capable of restructuring the brain's architecture at both structural and functional levels. From hippocampal damage to amygdala hypertrophy, from neuroinflammation to cognitive distortions, these changes lay the groundwork for mental disorders and reduce the quality of life. However, understanding these mechanisms paves the way for effective interventions, ranging from pharmacological methods targeting microglia to behavioral techniques that enhance psychological resilience.

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