What is ADHD?

Behind the Creative Brain

Written by Tori Throckmorton

Attention-Deficit/Hyperactivity Disorder (ADHD) is a collection of neurobiological traits that cause some areas of the brain to develop differently than in most human brains.

What Causes ADHD?

Scientists have unequivocally proven that genetics is the main factor in the development of ADHD. It has a heritability rate of 70 to 80% in both children and adults.

Translation: ADHD brains work differently than most people’s because they grew that way.

Researchers are still working hard to identify the various causes. Wait, causes? There’s more than one? There are many different genes involved and the characteristics those genes display depend heavily on environmental factors. Epigenetics is the study of how the environment affects how our genes work. The environment and our behavioral habits, especially during our developmental years, affect how our genes implement their code. Two individuals with the same gene will present very different traits according to things like how much sleep they got or how much stress they were exposed to as a child. This is the reason ADHD is so difficult to diagnose: each person has their own cocktail of ADHD characteristics. There’s a saying in the ADHD community “once you’ve seen one person with ADHD, you’ve seen ONE person with ADHD”.

Patients with ADHD show marked variation in profiles of symptoms, impairments, complicating factors, neuropsychological weaknesses and underlying causes. (Faraone, (2015), p. 9)

The different genetic causes also explain why about 30% of people with ADHD don’t benefit from stimulant medication, which stabilizes levels of the neurotransmitters dopamine and norepinephrine. These individuals still have challenges with hyperactivity and attention, but their symptoms must not be caused by the gene or genes impacting the production of neurotransmitters.

How are ADHD Brains Different?

While neurologists haven’t figured out everything that’s going on with ADHD brains, they have identified the main areas involved. To emphasize, not everyone with ADHD will have all these areas affected. It depends on your genes and the environment in which your brain developed.

I’m not a neurologist, or a scientist of any kind for that matter, so consider this a high-level overview of the buffet of ADHD neurological impacts. Before you try diagnosing yourself off of my amateur explanations, please keep in mind that not all the characteristics I describe can be used for diagnosis. Additionally, anyone reading this will have experienced one or more of these at some point in their life. Many of these characteristics also commonly occur with even minor sleep deprivation, as well as with aging and other mental conditions. In order to be considered ADHD, you must have displayed diagnosable traits starting in early childhood (prior to age 12)

Executive Control and Corticocerebellar Networks

The executive control and corticocerebellar networks control executive functioning: planning, goal-directed behavior, inhibition, working memory, and flexible adaptation to context. These areas are under-activated and have lower internal connectivity in individuals with ADHD. In particular, the parietal cortex handles the orientation of attention. The dorsolateral prefrontal cortex (PFC) handles working memory. And the ventromedial PFC takes care of complex decision-making and strategic planning.

What this can feel like:
  • Working memory: ever forget the one-time security code as soon as you looked up from the text message to type it in a website?
  • Planning and impulsivity: It’s Monday, and you have the entire week to prepare for a presentation on Friday and pack for a weekend camping trip. Every morning you plan to start working on the presentation but get sidetracked helping coworkers, answering emails, and other pop-up tasks. You finally start the presentation Thursday afternoon and end up staying up most of the night to finish it. You make it through the presentation on Friday and get a thumbs up from your boss. You crash on the couch until you hear a honk from the driveway. The camping trip! You burst into a flurry of frantic packing and make it out the door disheveled and exhausted.
  • Goal-directed behavior: You want to get in shape and intend to work out every day, but can’t seem to stick to it. You really want to look good for the summer but you just can’t seem to get out the door to the gym

Frontostriatal Circuit

The frontostriatal circuit is made up of the ventral and dorsal anterior cingulate cortices which support the ability to regulate emotions (1) and the cognitive components of executive control. The basal ganglia are known for the control of movement, behavior, and emotions. (2) Neuroimaging studies of patients with ADHD show structural and functional abnormalities in these structures, as well as the amygdala and cerebellum.

What this can feel like:

Reward System

The reward system is a center of the brain network that responds to anticipation and receipt of reward (think motivation). Behavioral and neural responses to reward are abnormal in ADHD. As a result, those with an ADHD brain prefer immediate over delayed rewards. Additionally, rewards that are closer seem more rewarding than ones that are far away.

What this can feel like:

I know I need to plan out my time each week but it’s such a boring chore. [Gets a new planner and pens] I’m so excited to plan out my week! [One month later] Ugh, time to plan out my week. Maybe after a couple of YouTube videos

Alerting Network

The alerting network supports attentional functioning and is weaker in individuals with ADHD. This is the network responsible for allowing us to tune out or disregard stimuli that aren’t relevant to our current activity.

What this can feel like:

Not being able to maintain a conversation in a crowd or a loud bar. You hear everything and can’t separate the voice of the person you’re talking to from the rest of the sounds.

Default-Mode Network (DMN)

The human brain has two modes: the DMN and the Task Positive Networks (TPN). The TPN is engaged for active tasks and the brain reverts to the DMN when there is no activity. Under normal operation, only one of these networks is active at a time. (3) In ADHD brains, they’ve shown that is often not the case and that we can have both competing for processing resources. Dr. Ned Hallowell refers to the DMN as the Demon because this is the system that can cause negative thought spirals and rumination.

What this can feel like:

Have you ever been driving and suddenly “woke up” or pulled into your driveway without remembering the drive home? That’s your TPN driving and your DMN occupying your attention.

Neurotransmitter circuits

Neurotransmitter circuits run throughout the brain, including each of the systems and networks already mentioned. The dopamine and noradrenergic system (norepinephrine) play a large role in the other systems we’ve discussed and, like many of the other systems mentioned, are under-active in ADHD. The dopamine system has an important role in planning and initiation of motor responses, activation, switching, reaction to novelty, and processing of reward. The noradrenergic system influences arousal modulation (emotional response), the signal-to-noise ratio in cortical areas, physical or psychological state-dependent (e.g. hunger, intoxication, physical location, stress) cognitive processes, and cognitive preparation of urgent stimuli.

Wow. How Could Anyone Get by with ADHD?

Now here’s the kicker. In certain situations, our brains work almost completely as a neurologist would expect of any human brain, and in some ways better. In addition to each individual’s particular genes, this “situational variability” is another reason ADHD is challenging to diagnose. It’s also the primary cause of our own doubts about having ADHD, even after we’ve been diagnosed. “But I did this just fine last week! Why can’t I do it now?”

Situational variability means that those diagnostic symptoms don’t happen all the time. And the different presentations of ADHD mean that someone won’t experience all the symptoms or each of them to the same degree. Another difference between an ADHD diagnosis and “everyone’s a little forgetful from time to time”, is one of the last items on the list of diagnostic criteria: “There is clear evidence that the symptoms interfere with, or reduce the quality of, social, school, or work functioning.” When ADHD affects school performance or results in routinely getting fired from jobs, the impact on quality of life is obvious. Less obvious are the situations in which our compensating behaviors successfully keep us “in the game” at school or work. But those strategies can come with a mental health cost that eventually gets too high to pay, many times resulting in burnout.

Whether you’ve known about ADHD for a while, you’re at the start of your journey, or going through the assessment process isn’t important to you, understanding your unique brain will enable you to consistently and more efficiently accomplish what is important to you. Understanding makes it possible to adapt your environment and habits to work with your brain. And if you’d like to have someone with the knowledge and resources to accelerate that process we’d be delighted to partner with you on your exploration!

Unless otherwise cited, all facts and scientific information on this page are referenced from:
Faraone, S., Asherson, P., Banaschewski, T. et al. Attention-deficit/hyperactivity disorder. Nat Rev Dis Primers 1, 15020 (2015). https://doi.org/10.1038/nrdp.2015.2

  1.  Schweizer, S., Grahn, J., Hampshire, A., Mobbs, D., Dalgleish, T. Training the Emotional Brain: Improving Affective Control through Emotional Working Memory Training. Journal of Neuroscience. 33 (12) 5301-5311. Published 20 March 2013. DOI: 10.1523/JNEUROSCI.2593-12.2013

  2. Lanciego JL, Luquin N, Obeso JA. Functional neuroanatomy of the basal ganglia. Cold Spring Harb Perspect Med. 2012;2(12):a009621. Published 2012 Dec 1. doi:10.1101/cshperspect.a009621

  3.  Hallowell, E. M., & Ratey, J. J. (2021). ADHD 2.0. Ballantine Books.

Learn more about...

Scroll to Top