Stress & the brain

Modern life is full of stress, worsened by the recent pandemic. As life begins to normalize, one of the lingering effects of the pandemic is increased rates of anxiety. Every body system is impacted by stress, especially the brain.

Before I continue, a quick reminder: I know I’ve written about this in many other posts but for those who are new to my blog: the type of stress I’m talking about here is chronic stress and it’s crucial to distinguish this from acute stress. The body’s response to acute stress, ie short term, is a fundamental and helpful survival mechanism and one which our bodies are designed for. This ‘fight or flight’ response actually sharpens cognitive function to help us cope with the stressful situation. Whereas chronic stress (where the stress continues over time) is harmful.

Exposure to chronic stress can lead to pathophysiological changes in the brain, which can manifest as behavioural, cognitive and mood disorders later in life. Researchers at University of California, Berkeley, have recently demonstrated that chronic stress can cause long-term changes in the brain. In the brains of PTSD patients, they observed a stronger link between the hippocampus and the amygdala (where the ‘fight or flight’ response occurs), and a weakened connection between the hippocampus and the prefrontal cortex (which is known as the ‘executive brain’ because it helps productivity by enabling focus and attention). Anxiety decreases the prefrontal cortex function and leads to an amygdaloid hyper-responsivity.

Did you know that stress can literally shrink your hippocampus? This is the part of the brain responsible for learning and memory. Studies have shown that it gets damaged easily and is associated with neurological and psychiatric illnesses such as Alzheimer’s and epilepsy. The hippocampus is particularly sensitive to stress because it has a large number of cortisol, oestrogen and progesterone receptors.

Chronic stress, which is associated with high cortisol levels, over time results in hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis. This is especially true for the area of the brain responsible for the regulation of mood and emotional responses, called the limbic area. Cortisol can cross the blood-brain-barrier and have long-lasting effects on the processing and cognition properties of the brain.

Chronic stress also causes neuroinflammation ie inflammation in the brain, which impairs neuronal transmission and plasticity. Neuroinflammation leads to neurodegenerative diseases like dementia, memory loss and depression.

Neuroinflammation is also a chronic stimulation of the immune system. A person suffering from chronic stress is more likely to have an impaired immune function and experience frequent illness.