The Cortisol Conundrum: The Stress Hormone Shaping Your Brain And Body
NEUROSCIENCE FINDS
Shirin Dhankhar
9/4/20264 min read
Imagine you're running late for an important meeting and your coffee spills down your shirt after tripping on air. Absolute ruin of a morning, yet miraculously you find your car keys, dodge traffic like it was ‘Crossy Roads’ in real life, and make it to the meeting 0.5 seconds early. This is your cortisol efficiently working like it was designed to.
Cortisol is a hormone in your adrenal glands that regulates your body’s response to stress. Acute, chronic, and traumatic stress all release cortisol which affects every organ in your body – from the brain to the gut – due to cortisol receptors at every interval. Immune responses to bone formation are all governed by this glucocorticoid. It lets you stay on high alert, and provides fast energy during times of stress.
Ever experienced purple stretch marks on your belly or muscle weakness in upper arms and thighs? Well, those symptoms of high cortisol along with high blood sugar and weight gains. On the other hand, low cortisol reverses signs of unintentional weight loss, fatigue, and loss of appetite. Ever heard of that low cortisol meme on the internet? Scientifically speaking, having low cortisol isn't truly beneficial.
The main functions of cortisol include regulating stress responses and blood pressure, balancing metabolism, suppressing inflammation, and controlling your sleep wake cycles. Did you know that cortisol is essential for sleep? It suppresses melatonin production and promotes energized mornings by peaking 30 minutes after waking up, declining throughout the day to reaching minimum around midnight. Due to chronic stress, cortisol is elevated all the time leading to fragmented and reduced REM sleep. It's a devastating loop – poor sleep impairs cognition, and stress management; leading to more stress due to decreased coping ability. According to a 2020 study in Psychoneuroendocrinology (that’s one big term!): One week of poor sleep leads to repairing the whole network over two weeks of consistent sleep quality. Now that we have discussed stress affecting the circadian rhythm, what about cognition?
The link between cortisol and cognitive performance follows a U shaped pattern called Yerkes-Dodson law. This suggests that at the low end of cortisol, you’re under-stimulated with attention flowing around like a lone leaf on a windy day with no sense of motivation directing you. Whereas on the high end, your leaf suddenly collapses due to a storm of too much cortisol disrupting neurotransmitter balance, resulting in panic and anxiety. However, not all stress is inherently bad. The middle is the sweetest spot where cortisol enhances your performance substantially such as sharpening memory and attention, completing deadlines, and cheekily letting you be charismatic during a first date. This curve also depends on how complex your task is, so different optimal levels are needed for running for your life or writing a book.
Having talked about how cortisol works, let’s dive into how your body actually controls production during stressful situations. The main neuroendocrine system is called the hypothalamic-pituitary-adrenal axis or HPA axis in short. It’s a three stage alarm system. Think of the amygdala as the brain’s threat detector. When it detects danger, it signals the hypothalamus which releases CRH (corticotropin-releasing-hormone). This travels to the pituitary gland which then releases ACTH (adrenocorticotropic hormone) into your bloodstream. ACTH reaches adrenal glands and cortisol levels rise up to increase heart rate, blood pressure, and makes you initiate a flight-or-fight response for hours. This whole process cascade takes about three minutes, rather than adrenaline which takes seconds. This is a negative feedback loop: hypothalamus and pituitary glands detect high cortisol levels and reduce their signaling. As mentioned before, chronic stress weakens this biological loop and the hypothalamus continues leaking CRH even when cortisol is already high. It’s a paradoxical response triggering brain damage. The three brain regions cortisol affects during chronic stress are:
Hippocampus: This seahorse shaped structure is important for forming new memories and spatial navigation. Due to having the most glucocorticoid receptors, it’s highly sensitive to cortisol causing hippocampal neurons to retract dendrites which leads to fewer synaptic connections and in the end impaired memory formation. It also makes the hippocampus volume smaller, suppresses neurogenesis (birth of new neurons) and in worst case scenarios kill neurons.
Prefrontal Cortex: Handling working memory, decision making, and impulse control – cortisol changes all of this. Even moderate stress triggers excessive dopamine and norepinephrine production to disconnect neural networks here. You can lose working memory and cognition drops and chronic stress similarity to hippocampus brings about dendritic retraction. Did you know pyramidal neurons in PFC (for cognitive control), lose 20% of their dendritic spine density?
Amygdala: Cortisol shrinking the aforementioned structures, actually does the opposite to the amygdala! Growing new dendrites and synaptic connections, this structure becomes more sensitive and reactive to fear, anxiety, and emotions.
I am sure everyone has had enough with the pessimistic notes, let’s think about reversing this brain damage. It’s possible, though not instantly. Exercise is the most powerful intervention as it reduces cortisol levels, improves HPA axis feedback, and increases hippocampal volume. Physical activity upregulates BDNF production (brain-derived neurotrophic factor which promotes neuron growth) and counteracts cortisol damage. Furthermore, getting a good 8 hours of sleep also helps balance out your circadian rhythm. Everyone has probably heard millions of times about mindfulness meditation but this genuinely does help by restoring PFC-amygdala connections and increasing gray matter density in the hippocampus while simultaneously decreasing it in the amygdala. Another prominent method is using neurofeedback which employs realtime brainwave monitoring to shift the brain out of the flight-or-fight response back to healthy self-regulation. Production of alpha and theta waves via audio and visual cues reduces stress and hyperarousal. Neurofeedback harnesses the brain’s own neuroplasticity!
