How Does Brain Structure Differ in Youth with ADHD Who Have a Family History of Bipolar Disorder?

What you need to know

• Youth with ADHD who have a family history of bipolar disorder show different patterns of brain connectivity compared to those without a family history.
• Both groups of youth with ADHD showed some similar brain differences compared to youth without ADHD, particularly in regions involved in attention and cognitive control.
• Youth with ADHD and a family history of bipolar disorder had unique changes in brain areas involved in emotional processing, which may be related to their increased risk for developing bipolar disorder.
• These findings could help identify youth with ADHD who may be at higher risk for developing bipolar disorder in the future.

Background on ADHD and Bipolar Disorder

Attention-deficit/hyperactivity disorder (ADHD) and bipolar disorder are two mental health conditions that can significantly impact a person’s life. ADHD is characterized by persistent problems with attention, hyperactivity, and impulsivity. Bipolar disorder involves episodes of depression alternating with periods of mania or hypomania (a milder form of mania).

Research has shown that ADHD is more common in youth who have a parent or sibling with bipolar disorder. Additionally, having both ADHD and a family history of bipolar disorder seems to increase the risk of developing bipolar disorder. However, scientists don’t fully understand the brain mechanisms behind this increased risk.

The Brain as a Network

To explore these brain mechanisms, the researchers in this study used an approach called graph theory to analyze brain imaging data. This approach looks at the brain as a complex network of interconnected regions, similar to a social network or the internet.

In this network model of the brain:

• Brain regions are represented as “nodes” (like individual people in a social network)
• Connections between regions are represented as “edges” (like friendships between people)

By examining how these nodes and edges are organized, researchers can learn about how efficiently information flows through the brain network and how well different brain regions work together.

The Study

The researchers recruited three groups of youth aged 10-18:

1. Youth with ADHD who had a parent or sibling with bipolar disorder (high-risk group)
2. Youth with ADHD who did not have any close relatives with bipolar disorder or other mood disorders (low-risk group)
3. Youth without ADHD or any family history of mood disorders (healthy control group)

All participants underwent magnetic resonance imaging (MRI) brain scans. The researchers then used graph theory techniques to analyze the structure of brain networks in each group.

Key Findings

Global Brain Network Differences

When looking at overall properties of brain networks, the researchers found that youth with ADHD and a family history of bipolar disorder (the high-risk group) showed some differences compared to healthy controls:

• Higher global efficiency: This suggests that information can travel more quickly between different parts of the brain network.
• Lower characteristic path length: This also indicates faster information flow across the brain network.

Interestingly, these global network differences were not seen in youth with ADHD who did not have a family history of bipolar disorder (the low-risk group).

Regional Brain Network Differences

When examining specific brain regions, both ADHD groups (high-risk and low-risk) showed some similar differences compared to the healthy control group:

• Changes in the default mode network (DMN): The DMN is a network of brain regions that is active when a person is not focused on the outside world. It’s involved in daydreaming, thinking about oneself, and remembering the past. Both ADHD groups showed alterations in how the DMN was connected to other parts of the brain.

• Changes in the central executive network (CEN): The CEN is involved in attention, working memory, and decision-making. Again, both ADHD groups showed differences in how this network was organized.

These findings align with previous research showing that ADHD is associated with changes in brain networks involved in attention and cognitive control.

Unique Findings in the High-Risk Group

The youth with ADHD and a family history of bipolar disorder showed some unique brain network changes that were not seen in the other groups:

• Alterations in the salience network: This network helps the brain decide what information to pay attention to and what to ignore. It’s also involved in switching between the default mode network and the central executive network.

• Specifically, there were changes in how a part of the brain called the inferior frontal gyrus was connected within the salience network.

These unique changes in the salience network may be related to the increased risk for developing bipolar disorder in youth with ADHD who have a family history of the condition.

Connections to Symptoms

The researchers also looked at how these brain network changes related to ADHD symptoms. They found that in both ADHD groups:

• Greater connectivity in a part of the brain called the right triangular inferior frontal gyrus was associated with more severe ADHD symptoms, particularly hyperactivity and impulsivity.

This suggests that changes in this brain region may be specifically related to the hyperactive and impulsive symptoms of ADHD.

What This Means for Understanding ADHD and Bipolar Disorder Risk

This study provides several important insights:

1. Youth with ADHD show some common brain network changes regardless of their family history of bipolar disorder. These changes are mainly in networks involved in attention and cognitive control.

2. Youth with ADHD who have a family history of bipolar disorder show additional, unique changes in brain networks involved in emotional processing and deciding what information is important.

3. These unique brain network changes in youth with ADHD and a family history of bipolar disorder may represent early warning signs or risk factors for developing bipolar disorder.

Limitations and Future Directions

It’s important to note some limitations of this study:

• The study only looked at brain structure at one point in time. Future studies that follow youth over time could help clarify whether these brain network changes actually predict who goes on to develop bipolar disorder.

• The high-risk group had more youth with the combined type of ADHD (involving both inattention and hyperactivity/impulsivity), while the low-risk group had more youth with the primarily inattentive type. This difference could account for some of the brain network changes seen.

Future research could:

• Follow youth over time to see how these brain network changes relate to the development of bipolar disorder
• Include larger groups of youth to better understand how ADHD subtype relates to brain network changes
• Investigate how these structural brain network changes relate to how the brain functions

Conclusions

• Youth with ADHD show some common brain network changes, particularly in regions involved in attention and cognitive control.
• Youth with ADHD who have a family history of bipolar disorder show additional changes in brain networks involved in emotional processing.
• These unique brain changes in youth with ADHD and a family history of bipolar disorder may represent early signs of increased bipolar disorder risk.
• Further research is needed to determine if these brain network changes can help predict which youth with ADHD are most likely to develop bipolar disorder in the future.