ADHD – brain structure and function – a focus on emotions and the amygdala
By Sophia DiLavore and Jim Stellar
ADHD, attention deficit hyperactivity disorder, is a neuropsychiatric disorder that causes inattention, hyperactivity, impulsivity, and motor restlessness. ADHD is often diagnosed during childhood as symptoms become apparent during academic, social, and family interactions. Approximately 5% of adolescents have been diagnosed with ADHD in contrast with 2.5-4.9% of adults. ADHD can persist into adulthood however sometimes impairments only partially persist.
It is important to understand the structural differences in an ADHD brain vs a healthy one which we can see by looking at brain scans. Most common brain scans include structural MRI (sMRI) for brain anatomy and functional magnetic resonance imaging (fMRI) for brain activity. Most size abnormalities of brain structures can be seen in adolescents in the prefrontal cortex, amygdala, hippocampus, and cerebellum.
Focusing first on the prefrontal cortex, the ADHD frontal cortex is 3-5% smaller than average. Given this brain area’s general reputation for inhibition of lower brain structure, this could explain deficits in inhibition, working memory, and other executive functions. Other difficulties in emotional regulation, motivation, and memory are attributed to irregularities in the amygdala and hippocampus. In this blog, a key focus will be on the amygdala.
The amygdala shown below from an fMRI scan is important in ADHD primarily because it regulates decision-making and controls situational behaviors in the environment whether it be instinctual or motivational behaviors. The amygdala has been known as the main brain structure involved in evaluating perceived sensory information then categorizing the stimuli into emotional dimensions such as valence, intensity and approachability.
By identifying the way in which the stimuli make a person feel, it allows for the person to distinguish whether or not the emotion is positive or negative and whether it is strong or weak. Smaller amygdala volume that is present in the ADHD brain produces altered emotional processing and perhaps less control of impulsivity.
Fear conditioning, a key role of the amygdala, is affected in the ADHD brain. Fear conditioning exemplifies associative learning as the brain creates memories about the relationship between two events. Fear triggers survival responses such as fight or flight or freeze, and it even seems to be integrated at a higher level into risk by the insula cortex. When humans detect fear the brain can even unconsciously trigger physiological responses as well as emotions. That could explain why people with ADHD perceive and react in situations dissimilarly than the average person. Specifically the basolateral amygdala (BLA) regulates social behavior and reward experience. Stimulation of the BLA relieves anxiety/freezing behavior (which is a fear reaction). The amygdala’s involvement in emotion perception is important in order to recognize social cues and react in survival situations. There are difficulties processing faces with emotional expressions which contributes to social problems for a person with ADHD. Adolescents with ADHD are commonly disliked by their peers and do not have many friends despite having an average intelligence.
Emotion recognition deficits also could be affected by the lack of dopaminergic receptors related to attention and reward seeking behavior and therefore a lower amygdala activation. This is true, even though dopamine has been largely associated with reward, not fear and that will be a subject of our next blog.
But here we want to make the point that, in general, emotional states influence selective attention, working memory, and cognitive control. For example, in normals as in ADHD subjects emotionally charged stimuli are more likely to register in memory (e.g. flashbulb memories) even though in ADHD subjects can have attention deficits. Emotions can enhance or interfere with memory depending on the duration and valence of the emotion(s). In another example, studies show that emotional distractors can cause short term negative effects on working memory as opposed to long term positive effects on episodic memory. We also know that people who are more susceptible to disruption due to emotional stimuli are likely to have higher activity in the amygdala, and as we have written, better connections between the frontal cortex and the amygdala produce more chill-type behavior in non-clinical subjects. Given that the amygdala mediates fear related memories and fear responses in seemingly anxious situations, that activation could trigger learning aversiveness. That is, people with ADHD could pull back from learning in general because they find it difficult due to challenges in maintaining attention.
Finally, on a related topic, the BLA is also associated with aggression which relates to fear responses and may lead to “Impulsive Aggression as a Comorbidity” as discussed in one study. In this study, they recommend further research to see how to control aggression when it appears in ADHD patients. But we know that in general the amygdala has a role in threat detection and can cause impulsive reactions in ADHD patients.
How does this inform the general purpose of this blog series about learning from experience? The essential feature of that operation we say is cognitive-emotional integration. Looking at ADHD provides a lens through which we can see the operation of that cognitive-emotional integration, and in this blog around the amygdala. Also, the ADHD patient is a variation of the normal college student. And finally, some college students (and others) have ADHD as part of the natural (and wonderful) variation of types of people that makes for a rich college environment. It also makes for opportunities to learn how to develop experiential programs that maximize the growth and learning of all college students.
