Therapy is a science. So is the process that creates mental health challenges. We often think about anxiety and depression as just a way that we feel, or even a part of our personality, but they’re actually changes in chemical balances and brain activities that are altered by some of the things going on in our lives.
These conditions alter our reality. They make us feel like what we’re thinking and feeling “is how it is,” and that it’s an accurate representation of the world and our place in it. Yet, what people are really experiencing is the way that chemicals in the body affect the way we think and feel.
That is why it is important to really understand both what is happening to create anxiety and depression, and also what therapy can do about it. While each person’s experience is different, these conditions tend to emerge through identifiable biological and psychological mechanisms that follow a predictable chain of events.
The Initial Stress Response
First, a note: Keep in mind that some conditions can occur without a clear cause, and some may be based on genetics more so than the process we will describe here. Still, it’s important to understand that even in cases where anxiety/depression are caused by genetics, it is still treatable with therapy.
Most cases of anxiety and depression begin with what we’ll call “sustained stress activation.” When a person encounters something that feels threatening – such as a demanding job, loss, or relationship conflict – the brain’s amygdala sends an alert to the hypothalamus. The hypothalamus then triggers the pituitary gland to release signals that activate the adrenal glands, producing stress hormones such as adrenaline and cortisol.
This is known as the “fight-or-flight” mode. Heart rate increases, attention narrows, and the body prepares for action as if you’re experiencing an actual, physical conflict rather than an emotional one.
In healthy situations, this system turns off when the stress passes. But when the stressor is ongoing – financial pressure, emotional trauma, or prolonged uncertainty – the body continues to release cortisol long after it’s needed.
This prolonged exposure begins to interfere with normal brain chemistry. Cortisol suppresses serotonin and dopamine production and damages neurons in the hippocampus, which regulates emotional memory. The longer the stress continues, the more the brain’s emotional regulation centers struggle to return to balance.
From Temporary Stress to Persistent Anxiety
When the body’s alarm system remains switched on, the amygdala becomes hypersensitive, meaning it begins to trigger the stress response even when no immediate threat exists. Everyday situations – emails, minor disagreements, or unfamiliar settings – start to feel tense or unsafe.
Meanwhile, the prefrontal cortex, which normally evaluates whether a threat is real, begins to lose efficiency. Its ability to override emotional impulses diminishes, allowing worry and tension to dominate thought.
As a result, anxiety develops as a learned biological habit: the brain associates ordinary experiences with danger, producing automatic fear or worry even when the logical mind knows there is no reason for alarm.
How Prolonged Stress Leads to Depression
If chronic stress continues without relief, the brain shifts from hyperarousal (anxiety) to fatigue and shutdown (depression). For some people, it may even skip the hyperarousal part altogether. After months or years of cortisol overproduction, the body begins to conserve energy. The stress system becomes blunted, reducing the release of both cortisol and the neurotransmitters responsible for motivation and pleasure – especially dopamine and norepinephrine.
This creates the physical foundation for depression. Activities that once brought enjoyment no longer produce reward responses in the brain. The dopaminergic pathways that signal satisfaction and purpose grow less active, while the default mode network – the part of the brain involved in self-referential thought – becomes more dominant. This shift increases rumination, self-doubt, and hopelessness.
At the same time, serotonin levels may fall, further reducing mood stability and increasing irritability. Sleep becomes disrupted as the body’s natural rhythm between alertness and rest loses coordination. Over time, this pattern reinforces itself: fatigue leads to reduced activity, which lowers dopamine and serotonin even further, deepening the depressive cycle.
The Role of Inflammation and Physical Health
Chronic stress also triggers inflammatory pathways. When cortisol remains high for long periods, immune cells release cytokines – chemical messengers that promote inflammation throughout the body. These cytokines can cross into the brain, altering neurotransmitter activity and reducing neuroplasticity.
Inflammation disrupts the function of serotonin-producing neurons and decreases the growth of new neural connections in the hippocampus. This helps explain why people experiencing ongoing physical illness, poor sleep, or poor nutrition often see increases in anxiety or depressive symptoms.
The body’s immune and stress systems are directly influencing brain chemistry, and vice versa.
When Brain Circuits Begin to Reinforce Each Other
As these chemical and structural changes take hold, the brain’s circuits begin to reinforce maladaptive patterns. The amygdala remains overactive, the hippocampus loses regulatory control, and the prefrontal cortex has less capacity to intervene. Thoughts become repetitive and self-critical because the neural networks that process threat and negativity are firing more frequently and with less inhibition.
This is why anxiety and depression can feel self-perpetuating. The brain’s chemistry, structure, and thought patterns are all reinforcing the same message – that something is wrong and cannot be changed.
You’ll hear someone tell you that mental health is self-sustaining, and this is why. When left untreated, it becomes a cycle that affects both a person’s thoughts and behaviors in ways that increase anxiety and negativity.
How the Process Can Be Reversed
Fortunately, the same neurobiological systems that create anxiety and depression can also recover. When stress levels decrease, when therapy helps regulate thought patterns, or when medication helps restore neurotransmitter balance, neuroplasticity allows the brain to form new pathways.
- Therapy (such as CBT, ACT, or mindfulness-based approaches) strengthens the prefrontal cortex’s ability to regulate emotion and reduces the amygdala’s hyperactivity.
- Exercise and improved sleep increase serotonin and dopamine production and lower inflammation.
- Antidepressant medication, when used appropriately, can normalize neurotransmitter activity and help the brain respond more effectively to positive experiences.
These interventions do not simply mask symptoms – they directly influence the underlying biological processes that created the problem.
Anxiety and Depression Are Biological Learning
In essence, anxiety and depression represent the brain’s attempt to adapt to prolonged stress. The brain learns to remain alert, cautious, or disengaged as a survival mechanism. What begins as a protective response becomes maladaptive when it no longer matches current circumstances.
By recognizing this, we can change our perspective of what it is and how it’s treated. These are not failures of character or perspective, but the result of identifiable neurochemical and structural patterns that can change with proper support.
The same biology that allowed anxiety and depression to form is the same biology that allows recovery. Through consistent care, therapy, and behavioral change, the brain can restore balance and rebuild resilience – proving that even the most deeply learned stress responses can be unlearned.