What is ADD?
ADD, or Attention Deficit Disorder, is a neurodevelopmental disorder characterized by inattention, hyperactivity and impulsiveness that interferes with functioning or development. Some key signs and symptoms include:
- Difficulty paying attention or staying focused on tasks
- Daydreaming and difficulty following instructions
- Forgetfulness and losing materials needed for tasks
- Disorganization, trouble finishing tasks and meeting deadlines
- Fidgeting or excessive talking
- Difficulty remaining seated
- Acting or speaking without thinking
- Trouble waiting or taking turns
ADD usually begins in childhood and can persist into adulthood. There are three main subtypes of ADD:
- Inattentive ADD – characterized mainly by difficulty focusing, disorganization and forgetfulness
- Hyperactive/Impulsive ADD – characterized by excessive activity, impulsiveness and restlessness
- Combined ADD – characterized by all of the above symptoms
ADD was previously known as Attention Deficit Hyperactivity Disorder (ADHD). The disorder is now recognized to not always include hyperactivity, hence the name change. Around 2-5% of adults are estimated to have ADD.
Is ADD a Brain Impairment?
ADD is considered a brain disorder and developmental impairment of the brain’s executive functions. Executive functions refer to cognitive skills that help regulate behavior and enable goal-directed actions. Core executive functions affected in ADD include:
- Impulse control
- Organization and planning
- Sustained attention
- Working memory
- Task switching
- Self-monitoring
Brain imaging studies show differences in brain structure and activity in people with ADD compared to those without the disorder. Specific brain differences found include:
1. Reduced Volume in Certain Brain Regions
MRI studies find people with ADD tend to have reduced volume in the frontal lobes, temporal gray matter, caudate nucleus, and cerebellum compared to those without ADD. These areas are involved in regulation of attention, emotions, inhibition and motor control.
2. Altered Brain Chemistry
Individuals with ADD show differences in dopamine and norepinephrine activity compared to those without the disorder. Specifically, they tend to have elevated dopamine transporters and reduced dopamine receptors in the brain. Dopamine and norepinephrine are key neurotransmitters involved in executive functions like attention and impulse control.
3. Differences in Brain Networks
Brain imaging shows those with ADD have disrupted connectivity between, and different activation of, large-scale brain networks including the:
- Default mode network (involved in internal thought processes)
- Executive control network (involved in cognitive control)
- Salience network (involved in switching between internal/external focus)
- Reward networks (involved in motivation and pleasure seeking)
4. Delayed Brain Maturation
Brain imaging studies show people with ADD have about a 3-year delay in cortical maturation, especially in the prefrontal cortex which is responsible for higher-order cognitive functions. This delayed development correlates with the onset and improvement of ADD symptoms in children.
Overall, these brain differences provide strong evidence that ADD involves structural and functional brain impairments. The brain variations underlie the executive function deficits and difficulty with attention, impulsivity and hyperactivity that characterize ADD.
Causes of Brain Differences in ADD
The exact causes of the brain differences seen in ADD are still being investigated. Current research suggests multiple factors contribute, including:
Genetics
ADD is a highly heritable disorder. Studies show 75-91% of differences in ADD symptoms are due to genetic factors. Specific genes involved regulate dopamine, serotonin and norepinephrine activity in the prefrontal cortex and other brain regions important for attention and inhibitory control.
Environmental Factors
Factors like prenatal exposure to nicotine, alcohol or toxins, premature birth, brain injury and psychosocial adversity have been associated with increased risk of developing ADD. They likely exert effects by altering early brain development.
Differences in Brain Structure
Structural brain abnormalities related to the size of the prefrontal cortex, white matter volume and asymmetry between the brain hemispheres have been linked to increased ADD risk and appear present early in development.
Brain Chemical Imbalances
Imbalances in key neurotransmitters like dopamine and norepinephrine due to reduced receptors or excess transporters disrupt neural communication in brain regions that enable executive functions and self-control.
| Factor | Evidence |
|---|---|
| Genetics | 75-91% heritability; gene variants affect dopamine, serotonin, norepinephrine |
| Environment | Prenatal exposure to substances; premature birth; brain injury; psychosocial adversity |
| Brain structure | Prefrontal cortex size; white matter volume; hemispheric asymmetry |
| Brain chemistry | Dopamine, norepinephrine activity imbalances |
How Brain Differences Cause ADD Symptoms
The brain abnormalities observed in ADD directly undermine key cognitive capacities like attention, inhibition, motivation and memory. Specifically:
- Reduced prefrontal and temporal lobe volume negatively affects regulation of attention, emotions, behavior.
- Imbalanced dopamine and norepinephrine reduce ability to focus and control impulses.
- Disrupted connectivity between brain networks impairs ability to switch attention, control behavior, inhibit distractions.
- Delayed brain maturation is linked to later emergence of executive functions like working memory, organization.
Together, these brain impairments make it very difficult for people with ADD to consistently:
- Pay attention and avoid distractions
- Organize, plan and manage time/materials needed for tasks
- Regulate emotions, inhibit inappropriate behaviors
- Delay gratification and sustain mental effort for long periods
Trying to function with these impairments leads to the hallmark symptoms of inattention, impulsivity, hyperactivity and disorganization characteristic of ADD.
Inattention
Reduced ability to control attention makes it hard to stay focused on tasks, leading to forgetfulness, distractedness and difficulty completing work.
Impulsivity
Deficits in inhibitory control result in impulsive behaviors like interrupting others, difficulty waiting, blurting out answers before questions have been fully asked.
Hyperactivity
Seeking stimulation to increase low dopamine levels can prompt excessive movement, fidgeting, restlessness and difficulty staying seated.
Disorganization
Impairments in planning, prioritizing and working memory make it hard to systematically complete tasks and meet deadlines.
Evidence from ADD Treatments
The effectiveness of treatments for ADD provides additional evidence it is caused by underlying brain impairments.
Stimulant Medications
Stimulants like methylphenidate (Ritalin) and amphetamine salts (Adderall) help improve ADD symptoms by increasing dopamine and norepinephrine activity in the prefrontal cortex. This compensates for chemical imbalances underlying difficulties with executive functions.
Non-stimulants
Non-stimulant medications like atomoxetine (Strattera), guanfacine (Intuniv) and clonidine (Kapvay) also improve ADD symptoms. They work by selectively targeting norepinephrine and dopamine pathways in the brain.
Behavioral Therapy
Behavior therapies help strengthen executive function and coping skills to compensate for ADD-related brain deficits. Cognitive-behavioral therapy, coaching and skills training can teach strategies to improve organization, time management and inhibitory control.
The fact that treatments targeting brain chemicals and functions improve ADD symptoms supports it stems from underlying neurological impairments.
Is ADD a Learning Disability?
ADD shares many similarities with learning disabilities, though there are some distinctions:
Overlap with Learning Disabilities
– Both involve differences in brain structure and function that affect certain cognitive skills.
– People with ADD and learning disabilities often have impairments in executive functions like working memory, organization and impulse control.
– ADD and learning disabilities often co-occur, around 31% of those with either disorder have both conditions.
Distinguishing Features of ADD
– Learning disabilities are diagnosed based on impaired academic achievement in specific areas like reading, writing or math. ADD is not specific to certain academic skills.
– ADD involves more widespread executive function deficits including sustained attention, inhibition, motivation and time management.
– ADD is characterized by clinically significant inattention, hyperactivity and impulsivity. Learning disabilities do not necessarily involve these behavioral symptoms.
– ADD symptoms impair function in school, work and relationships. Learning disabilities impact schoolwork but may not always impair other areas.
While there is overlap, ADD has a more global effect on executive functions that impairs attention, behavior and functioning across multiple settings.
Conclusion
In conclusion, extensive research evidence supports that ADD is caused by structural and functional brain impairments:
- Brain imaging shows differences in brain anatomy, activity and neurotransmitter balances in people with ADD.
- Genetic vulnerabilities, developmental and environmental factors contribute to ADD brain differences.
- The brain variations observed directly disrupt cognitive skills like sustained attention, working memory, inhibition and motivation.
- Impairments in these executive functions lead to the hallmark symptoms of ADD.
- Treatments targeting brain activity improve ADD symptoms.
Though some contend ADD is an invented disorder or merely the result of motivational deficits, empirical evidence firmly establishes ADD as a legitimate neurodevelopmental disorder caused by underlying neurological impairments. Identifying and managing these brain differences is key to helping those with ADD reach their full potential. With appropriate support and tools to compensate for their deficits, people with ADD can thrive academically, socially and in the workplace.