How Do Depression and Anxiety Interact in the Brain?

What you need to know

• Depression and anxiety frequently occur together, causing more severe impairments than either disorder alone.
• Recent research has identified unique brain patterns and symptoms that distinguish depression from anxiety, despite their overlap.
• New computational approaches are providing insights into how depression and anxiety differently affect decision-making and risk assessment.

The Complex Relationship Between Depression and Anxiety

Depression and anxiety are two of the most common mental health conditions, affecting millions of people worldwide. While they are considered separate disorders, depression and anxiety frequently occur together in what’s known as comorbidity. When someone experiences both depression and anxiety, their symptoms are often more severe, recovery is slower, and the risk of suicidal thoughts is higher compared to having just one of these conditions.

This high rate of overlap has led some researchers to question whether depression and anxiety are truly distinct disorders or if they represent different aspects of a single underlying problem. However, recent studies have uncovered important differences in how depression and anxiety manifest in the brain and behavior, even when they occur together. This article explores the latest research on the complex relationship between depression and anxiety.

Identifying Patterns in Symptoms

Researchers have been using advanced statistical techniques to look for patterns in how symptoms of depression and anxiety show up in different people. One method, called latent class analysis, groups people based on the specific combination of symptoms they experience.

These studies have consistently found a group of people who have symptoms of both depression and anxiety. Interestingly, this combined depression and anxiety pattern shows up at different levels of severity - some people have mild symptoms of both, while others have more intense symptoms.

People in this combined depression and anxiety group tend to share certain characteristics:

• They are more likely to be female
• They tend to be younger
• They often have fewer years of education
• They report experiencing more stressful life events

Another technique called network analysis looks at how different symptoms are connected to each other. This research has identified certain symptoms that seem to bridge between depression and anxiety:

• Feeling restless or slowed down (changes in physical activity level)
• Irritability

These “bridge symptoms” may help explain why depression and anxiety so often occur together. At the same time, some symptoms appear to be unique to depression, such as changes in appetite and thoughts of suicide.

Brain Differences in Depression and Anxiety

Early brain research suggested that depression and anxiety involve similar changes in brain areas involved in emotion and stress responses. However, more recent studies have found some key differences:

• A study using transcranial magnetic stimulation (a technique that can activate specific brain regions) found that stimulating one area of the prefrontal cortex reduced anxiety symptoms, while stimulating a different prefrontal area reduced depression symptoms. This suggests that distinct brain circuits may be involved in anxiety versus depression.

• Both depression and anxiety have long been associated with changes in the stress hormone system, particularly elevated levels of the hormone cortisol. However, new research indicates there may be more variation in these hormone changes than previously thought. Some types of anxiety disorders may involve different cortisol patterns than depression.

These findings highlight that while depression and anxiety share some common brain features, there are also important differences in the specific brain circuits and hormone patterns involved in each condition.

How Depression and Anxiety Affect Decision-Making

An emerging field called computational psychiatry is providing new insights into how depression and anxiety impact cognitive processes like decision-making. This approach uses mathematical models to simulate the brain processes underlying behavior, allowing researchers to identify very specific changes in how people think and make choices.

Some key findings from this research include:

• Depression is associated with reduced reward-seeking behaviors. People with depression tend to:

  • Learn more slowly about potential rewards in their environment
  • Overestimate how much effort is required to obtain rewards
  • Have a harder time remembering positive past experiences

• Anxiety is linked to heightened sensitivity to potential threats and increased avoidance behaviors. People with anxiety tend to:

  • Be more aware of and reactive to possible dangers
  • Make choices that prioritize avoiding negative outcomes, even if it means missing out on rewards

• When it comes to assessing risks, anxiety seems to play a bigger role than depression. People with higher anxiety levels tend to be more risk-averse, meaning they’re less likely to take chances even when the potential payoff is high.

• Depression may change how people evaluate probabilities, particularly for positive outcomes. As depression symptoms increase, people become less likely to overestimate the chances of rare positive events and underestimate the chances of likely positive events.

These findings show that while both depression and anxiety can impact decision-making, they do so in distinct ways. This may help explain some of the differences in behavior seen between these conditions.

Conclusions

• Recent research has greatly advanced our understanding of how depression and anxiety are similar and different in terms of symptoms, brain function, and effects on thinking and behavior.
• While depression and anxiety frequently occur together and share some common features, there are also important distinctions between these conditions.
• Identifying the unique characteristics of depression, anxiety, and combined depression-anxiety may lead to more targeted and effective treatments in the future.