All About ADHD

What is ADHD?

Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder of attention, concentration, impulsivity, and hyperactivity. ADHD is one of the most heritable psychiatric disorders and the most common behavioral disorder in children.

Although ADHD was originally thought to be a disorder exclusively in children, we now know that approximately two-thirds of children diagnosed with ADHD experience impairing symptoms in adulthood. In school-aged children/adolescents, the prevalence of ADHD is about 5-7%. There are different types of ADHD depending on whether symptoms are predominantly inattentive, hyperactive, or both. The combined type is the most common type in children and adolescents.

Males are more likely diagnosed in childhood and adolescence, likely because males display more hyperactive symptoms than females and therefore are more likely to be referred for evaluation.

Females usually have more inattentive symptoms and aren’t diagnosed until later in life. This is supported by the more equal prevalence of ADHD in adult males and females. The inattentive type is the most prevalent type in adults (about 47% of cases). The apparent decrease in hyperactive-impulsive symptoms as individuals age is likely related to the maturation of brain circuits in the cerebral cortex as people age. 

Symptoms of ADHD include inattention, hyperactivity, and impulsivity that interferes with an individual’s relationships, work, schooling, or other important areas of functioning. 

  • Difficulty with attention to detail
  • Often makes careless mistakes
  • Difficulty listening when spoken to directly (e.g., mind seems to wander elsewhere).
  • Difficulty following directions
  • Difficulty organizing tasks and activities
  • Often avoids tasks requiring sustained mental effort
  • Often loses things/personal items 
  • Often is easily distracted
  • Often forgetful about daily activities
  • Often has difficulty sustaining attention
  • Often bored or loses interest quickly
  • Often fidgets or shifts in seat (example: meditation can be very difficult for those with ADHD)
  • Often leaves seat in situations when remaining seated is required 
  • In children, often runs about or climbs in situations where it is inappropriate
  • Often unable to play or engage in leisure activities quietly
  • Internal restlessness or feeling constantly on the go
  • May talk excessively
  • Often finishes sentences or blurts out answers
  • Often has difficulty waiting his or her turn
  • Often interrupts others 
  • Often impatient 

What is Attention?

Attention is a cognitive function. Attention describes the process of determining the importance of various stimuli and selecting the stimuli most relevant to the task at hand. Attention is an important component of our consciousness.

Which Brain Areas are Involved in Attention?

Although neural networks throughout the entire brain contribute to most cognitive functions, there are some areas of the brain which appear to play a greater role in remaining attentive. These areas include the prefrontal cortex (which is part of the frontal lobe or frontal region of the brain) and the regions “underneath” or “embedded” in the frontal lobe such as the cingulate cortex and its connections with the nondominant parietal lobe. 

Reward and Impulse Control

Controlling the impulse to take an immediate, smaller reward rather than waiting for the larger, delayed reward is essential for completing any project. People who cannot control these impulses often fall behind. In the famous Stanford Marshmallow Experiments of the 1970s, Walter Mischel, a psychologist, conducted a very interesting experiment:
Four-year-old children were given one marshmallow. These children were told that they could either eat the marshmallow now or wait until the research assistant returned from an errand and receive TWO marshmallows (oh my!). Some children couldn’t wait for the assistant to return and immediately ate the marshmallow in front of them. Others waited a little but eventually ate the marshmallow. And yet others waited until the assistant returned and were rewarded with TWO marshmallows (what a reward!). 

The children in the study were followed into adolescence and adulthood. It turned out that the children who were better at inhibiting the impulse to immediately eat the one marshmallow were more resilient, confident, and dependable as adolescents. They also scored higher on standardized tests such as the SAT. While a controversial study with some methodological problems, the results were interesting, nonetheless.

Dopamine and Norepinephrine 

Dopamine and norepinephrine are two very important brain chemicals involved in attention, movement, and impulse control. These two chemicals work together to filter out irrelevant stimuli while enhancing the relevant stimuli. In individuals with ADHD, these two chemicals appear to be imbalanced or “out of tune.” By enhancing these brain chemicals with medications, therapy, and neurofeedback, we can improve symptoms dramatically!


Attention and impulsivity are partially controlled by dopamine (DA) in an area of the brain called the Nucleus Accumbens (NAc). The NAc, which is part of the striatum (another brain region), is the part of our brain responsible for pleasure, motivation, and reinforcement. Stimulant medications such as Concerta, Ritalin, Focalin, Adderall, Dexedrine, and Vyvanse increase dopamine release in the NAc to improve our ability to control impulsive behaviors. Interestingly, rats with damage to their NAc are more impulsive–they almost always choose the immediate reward.

Brain Changes in ADHD

Changes in the prefrontal cortex (PFC) and striatum are the most common abnormal brain findings reported for ADHD. Judith Rapoport’s National Institute of Mental Health (NIMH) neuroimaging studies have revealed interesting findings in children with ADHD. Children with ADHD, on average, have smaller brain volumes by about 5% and also have smaller cerebellums (the little brain in the back of the brain). Importantly, the trajectory of brain volumes did not change as the children aged, nor was it affected by the use of stimulant medication.
When comparing children with and without ADHD, there was significantly greater activity in the parietal and frontal lobes of children without ADHD during an attention task (see figure below). This tells us that decreased activity in the frontal and parietal lobes may be partially responsible for inattentiveness. That is, these brain areas aren’t activated enough or “online” during attention-requiring tasks. 

ADHD & Gender Differences

The symptoms of ADHD present slightly differently in males and females. A list of differences is provided in the table below.

Consequences of Untreated ADHD

  • A World Health Organization survey estimated that 3.5% of all workers suffer from ADHD yet only a minority of these workers received treatment. 
  • Young adults diagnosed with ADHD but not treated are less likely to enroll in college or graduate from college.
  • Students with untreated ADHD are more likely to be on academic probation and have a lower grade point average.
  • Adults with untreated ADHD experience difficulties in all aspects related to employment
  • ~20% of parents of children with ADHD have ADHD themselves (Faraone et al. 2000).
  • Untreated ADHD has been associated with significantly increased risk of developing substance use disorders
  • Untreated ADHD has been associated with risky behaviors resulting in traffic tickets, motor vehicle accidents, and other injuries related to impulsivity and altered decision-making 

ADHD and Criminality 

  • Studies have estimated the prevalence of ADHD among male prison inmates to be around 40% (Rösler et al. 2004; Ginsberg et al. 2010).
  • In the absence of comorbid conduct disorder, ADHD patients had no higher risk for delinquency than adults with other childhood psychiatric disorders (Gjervan et al. 2012).

ADHD Symptoms in Adults

  • Hyperactivity: Inner restlessness, Talkativeness, Excessive fidgeting, high risk activities
  • Impulsivity: Impatience – “talking without thinking”, difficulty maintaining employment, difficulty maintaining relationships, attention seeking behavior, high risk behaviors, self-medicating
  • Inattentiveness: Feeling bored, indecisive, procrastination, disorganization, easily distracted

Common complaints in Adults with ADHD

  • Common complaints in adults with ADHD include rapid mood swings, difficulties dealing with stressful situations, frequent irritability and frustration, emotional excitability (anger over minor things), relationship problems (short-lived, divorce), and coping with one or more children with ADHD.


ADHD vs Bipolar Disorder

Differentiating ADHD from Bipolar Disorder can be difficult because many symptoms overlap and both disorders often co-occur (that is, many patients have both ADHD and Bipolar Disorder). Below is a table differentiating the two.

Treatment Options For ADHD

  • Medications (Stimulants, nonstimulants)
  • Behavioral therapy 
  • Neurofeedback
  • Biofeedback

ADHD and Substance Use Disorders

NOTE: Stimulants such as amphetamines (Adderall, Dexedrine, Vyvanse) and methylphenidates (Ritalin, Concerta, Focalin) are first-line treatments for adult ADHD. Studies suggest that amphetamines may be more effective for adult ADHD symptoms than methylphenidates. The common belief that individuals with a history of substance abuse shouldn’t be prescribed psychostimulants is not supported by empirical or anecdotal evidence. In fact, proper treatment of ADHD symptoms has been associated with a reduction in substance use. For more information on this, please see the articles below.

ADHD Medication and Substance-Related Problems 

Stimulant ADHD medication and risk for substance abuse


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