Anxiety is a common yet complex emotion that has evolved as part of our brain’s mechanism for survival. As outlined in the first post in the Anxiety Series, it is a normal reaction to stress and uncertainty but when it becomes chronic, anxiety can have significant impacts on an individual’s mental and physical health. In this post, I will delve into the science behind anxiety, key areas of the brain’s structure, the neurochemistry involved, and the physiological changes that occur during an anxious state. By understanding these processes, we can better appreciate why anxiety exists, how it manifests, and how to manage it.
The brain’s role in anxiety – the amygdala & the prefrontal cortex
The regions in the brain most closely associated with anxiety are the amygdala and the prefrontal cortex.
The amygdala is an almond-shaped structure deep within the brain that plays a crucial role in processing emotions, especially fear. When faced with a perceived threat, the amygdala sends out signals that initiate the body’s ‘fight-or-flight’ response, preparing us to react to danger. This process involves releasing stress hormones like cortisol and adrenaline, which increase heart rate, elevate blood pressure, and sharpen focus.
The prefrontal cortex, which is responsible for higher order thinking e.g. critical thinking, decision-making and impulse control, acts as a counterbalance to the amygdala’s reactivity. It helps to evaluate whether a threat is real and if the body’s stress response is justified. In individuals with anxiety disorders, this balance can be disrupted. The amygdala may become overactive, whilst the prefrontal cortex struggles to regulate its response, leading to heightened anxiety even in non-threatening situations.
Neurotransmitters & anxiety
Neurotransmitters are chemicals that transmit signals between nerve cells in the brain. Several neurotransmitters are closely linked to anxiety but three are particularly important: gamma-aminobutyric acid (GABA), serotonin, and norepinephrine.
– GABA (Gamma-Aminobutyric Acid): GABA is the brain’s primary inhibitory neurotransmitter meaning it works to calm the nervous system. It inhibits excessive neural activity, helping to keep anxiety levels in check. When GABA levels are low or its receptors are not functioning properly, the brain can become overly excitable, leading to heightened anxiety and stress.
– Serotonin: Serotonin plays a crucial role in maintaining emotional stability helping to modulate anxiety by influencing mood, appetite and sleep. When there are low levels of serotonin or dysfunction in its pathways, they are commonly linked to anxiety disorders. Additionally, selective serotonin reuptake inhibitors (SSRIs) are a common class of antidepressants. They work by increasing serotonin levels in the brain, which can help alleviate symptoms of anxiety.
– Norepinephrine: This neurotransmitter is involved in the body’s “fight-or-flight” response and can increase alertness, heart rate, and blood pressure. High levels of norepinephrine are often found in people experiencing acute stress or panic attacks. Its role in anxiety is complex. It helps prepare the body to respond to threats but, in excess, contributes to symptoms like restlessness and hyper vigilance.
The role of the hypothalamic-pituitary-adrenal (HPA) axis
The hypothalamic-pituitary-adrenal (HPA) axis is a complex system that governs the body’s response to stress. When the brain perceives a stressor, the hypothalamus releases a hormone called corticotropin-releasing factor (CRF). CRF stimulates the pituitary gland to release adrenocorticotropic hormone (ACTH). ACTH then triggers the adrenal glands to release cortisol, the primary stress hormone.
Cortisol helps us self-regulate during times of stress by increasing energy levels, enhancing the immune response and regulating blood pressure. However, chronic stress and prolonged activation of the HPA axis can lead to sustained high levels of cortisol. This may contribute to anxiety and even physical health problems like cardiovascular disease. In people with anxiety disorders, the HPA axis can become dysregulated which results in an exaggerated stress response.
Genetics & anxiety
Whilst environmental factors like trauma, upbringing and life experiences play a significant role in anxiety, genetics also contribute to an individual’s susceptibility to anxiety disorders. Studies have shown that anxiety has a heritable component. In fact, genetic factors account for approximately 30-40% of the risk for developing conditions like generalised anxiety disorder or panic disorder 1,2. Specific genes involved in neurotransmitter regulation, such as those that influence serotonin and GABA pathways, can increase the likelihood of experiencing anxiety.
Research into the genetic basis of anxiety is ongoing. For instance, a recent study of 1m participants by Yale University found that there are 100+ genes associated with anxiety 3. Scientists are studying variations in genes like the serotonin transporter gene (5-HTTLPR) and how these may impact an individual’s vulnerability to stress. Whilst having a genetic predisposition does not guarantee the development of an anxiety disorder, it can make an individual more sensitive to stressful events.
The fight-or-flight response & physical symptoms
One of the most striking aspects of anxiety is its physical manifestation. The fight-or-flight response is triggered by the amygdala and supported by the release of stress hormones. This prepares the body to either confront or flee from a perceived danger. This physiological response includes a range of symptoms, such as:
– Increased heart rate: The heart pumps more blood to prepare muscles for action which can lead to palpitations or a sensation of a racing heart.
– Rapid breathing: To deliver oxygen to muscles, breathing becomes faster, sometimes causing hyperventilation and shortness of breath.
– Sweating: The body releases sweat to cool down and causes clammy hands or excessive perspiration.
– Muscle tension: Muscles tighten as the body prepares for physical action leading to tension headaches or aching in the body.
These physical symptoms are natural in the short term. However, symptoms become distressing and problematic when they occur without clear external threats.
The role of cognitive biases in anxiety
Beyond the biological factors, cognitive processes play a crucial role in anxiety. Someone with an anxiety disorder often presents with cognitive biases. These include a tendency to overestimate the likelihood of negative events or focus on potential threats more than positive outcomes. These cognitive distortions perpetuate a cycle of anxiety by reinforcing the brain’s perception of the world as a dangerous place
Conclusion: A multifaceted experience
Anxiety is a multifaceted experience that involves a complex interplay between the brain, neurotransmitters, genetic and cognitive processes. It has an essential role in keeping us alert to danger, but becomes debilitating when it persists in the absence of real threats. By understanding the science behind anxiety, we gain valuable insights into why it occurs and how we can better manage it.
You can read more about the different types of anxiety and how they show up in the next part of the Anxiety Series. Read Part 3: The Different Forms of Anxiety
1 Gottschalk, M. G., & Domschke, K. (2017). Genetics of generalized anxiety disorder and related traits. Dialogues in clinical neuroscience, 19(2), 159–168. https://doi.org/10.31887/DCNS.2017.19.2/kdomschke
2 Hettema J.M., Neale M.C. & Kendler K.S. (2001) A review and meta-analysis of the genetic epidemiology of anxiety disorders. American Journal of Psychiatry, 158(10), 1568-78.https://psychiatryonline.org/doi/10.1176/appi.ajp.158.10.1568.
3 Yale School of Medicine (2024). Yale Scientists Uncover Genetic Predisposition to Anxiety. Retrieved from https://medicine.yale.edu/center-clinical-investigation/news-article/yale-scientists-uncover-genetic-predisposition-to-anxiety/ [Accessed 23/10/2024]
