What is ADHD?

Attention Deficit Hyperactivity Disorder, more commonly referred to as ADHD, is a neurodevelopmental disorder, which means the brain is affected.  ADHD is more commonly diagnosed in boys than girls and current prevalence ratios are generally estimated at 2–5:1, while clinic populations show a ratio as high as 10:1 (NICE).  In the UK, the prevalence of ADHD in adults is estimated at 3% to 4%, with a male-to-female ratio of approximately 3:1 (NICE).

While no specific biomarkers have been found, there is strong evidence to suggest a genetic component and studies have confirmed ADHD to be hereditary (Larsson et al 2013 & 2014).  Other identified risk factors for ADHD include pregnancy and early childhood risk factors (premature birth, low birth weight, maternal smoking during pregnancy) as well as socioeconomic risk factors (lower socioeconomic strata, single-parent households & maternal depression) (Johnson, Morris & George, 2020).

  • People with ADHD have slightly different brain structures to the neurotypical population; this includes abnormalities in both grey & white matter as well as brain volume.  There are also differences in certain brain regions, such as the prefrontal cortex, cerebellum, hippocampus, and amygdala, which may be smaller in volume.  While some studies have also found increased connectivity in deep brain structures (the limbic system) and the frontal areas (associated with attention and control).  All of these differences, mean people with ADHD often face challenges around executive functions such as prioritising and planning, impulse control and paying attention. 

  • Adults with ADHD can often experience difficulties in switching between tasks.  This ability is controlled by the default mode network (DMN) and the cognitive control network (CCN); these are essentially an automatic on/off switch.  For adults with ADHD, it may be harder to switch these networks on or off to enable full concentration on a task.

  • ADHD is ultimately the result of a neurotransmitter deficiency, in this case Norepinephrine which helps to control the brains pleasure and reward capabilities.

    Check out these links for more information about how ADHD affects brain function:

    Inside the ADHD Brain: Structure, Function, and Chemistry - ADDA - Attention Deficit Disorder Association

    The ADHD Brain: Neuroscience Behind Attention Deficit Disorder

Symptoms of ADHD in adults

These are the symptoms of ADHD in adults as defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5).  This is the official diagnostic criteria someone’s symptoms must meet to be diagnosed with ADHD.

The DSM categorises the symptoms of adult ADHD as follows:

·       A persistent pattern of inattention and/or hyperactivity-impulsivity that interferes with functioning or development,

·       Often fails to give close attention to details or makes careless mistakes in schoolwork, at work, or during other activities

·       Often has difficulty sustaining attention in tasks or play activities 

·       Often does not seem to listen when spoken to directly

·       Often does not follow through on instructions and fails to finish schoolwork, chores, or duties in the workplace

·       Often has difficulty organizing tasks and activities

·       Often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort

·       Often loses things necessary for tasks or activities

·       Is often easily distracted by extraneous stimuli 

·       Is often forgetful in daily activities

·       Often fidgets with or taps hands or feet or squirms in seat

Types of ADHD

It is important to remember that everyone is unique and people’s symptoms can differ.  The following are the symptoms as classified by the DSM criteria.

    • Difficulty maintaining attention

    • Doesn’t seem to listen when spoken to

    • Easily distracted

    • Struggles to stay focused on boring tasks

    • Problems organising activities and tasks

    • Forgetful and often loses things

    • Doesn’t follow through on instructions

    • Makes careless mistakes

  • o   Often squirms or fidgets

    o   Struggles to engage in activities quietly

    o   Leaves the room or stands when expected to remain seated

    o   Constant feelings of restlessness

    o   Difficulty waiting your turn

    o   May blurt out answers before a question is finished

    o   Talking excessively

    o   May interrupt others or intrude

  • o   Symptoms from both of the above are present

·       Often leaves seat in situations when remaining seated is expected

·       Often runs about or climbs in situations where it is inappropriate

·       Often unable to play or take part in leisure activities quietly

·       Is often “on the go” acting as if “driven by a motor” 

·       Often talks excessively

·       Often blurts out an answer before a question has been completed

·       Often has trouble waiting his/her turn

·       Often interrupts or intrudes on others

·       Several inattentive or hyperactive-impulsive symptoms were present before age 12 years

·       Several inattentive or hyperactive-impulsive symptoms are present in two or more settings

·       There is clear evidence that the symptoms interfere with, or reduce the quality of, social, school, or work functioning

·       The symptoms do not occur exclusively during the course of schizophrenia or another psychotic disorder and are not better explained by another mental disorders.

Other Helpful Research:

[1] Liu, Y., Zhao, J., & Guo, W. (2018). Emotional Roles of Mono-Aminergic Neurotransmitters in Major Depressive Disorder and Anxiety Disorders. Frontiers in Psychology, 9. https://doi.org/10.3389/fpsyg.2018.02201

[2] Ulke, C., Rullmann, M., Huang, J., Luthardt, J., Becker, G. A., Patt, M., Meyer, P. M., Tiepolt, S., Hesse, S., Sabri, O., & Strauß, M. (2019). Adult attention-deficit/hyperactivity disorder is associated with reduced norepinephrine transporter availability in right attention networks: a (S, S)-O-[11C]methylreboxetine positron emission tomography study. Translational psychiatry, 9(1), 301. https://doi.org/10.1038/s41398-019-0619-y

[3] del Campo, N., Chamberlain, S. R., Sahakian, B. J., & Robbins, T. W. (2011). The Roles of Dopamine and Noradrenaline in the Pathophysiology and Treatment of Attention-Deficit/Hyperactivity Disorder. Biological Psychiatry, 69(12), e145–e157. https://doi.org/10.1016/j.biopsych.2011.02.036

[4] Volkow, N. D., Wang, G. J., Kollins, S. H., Wigal, T. L., Newcorn, J. H., Telang, F., Fowler, J. S., Zhu, W., Logan, J., Ma, Y., Pradhan, K., Wong, C., & Swanson, J. M. (2009). Evaluating dopamine reward pathway in ADHD: clinical implications. JAMA, 302(10), 1084–1091. https://doi.org/10.1001/jama.2009.1308

[5] Gehricke, J. G., Kruggel, F., Thampipop, T., Alejo, S. D., Tatos, E., Fallon, J., & Muftuler, L. T. (2017). The brain anatomy of attention-deficit/hyperactivity disorder in young adults – a magnetic resonance imaging study. PloS one, 12(4), e0175433. https://doi.org/10.1371/journal.pone.0175433

[6] Plessen, K. J., Bansal, R., Zhu, H., Whiteman, R., Amat, J., Quackenbush, G. A., Martin, L., Durkin, K., Blair, C., Royal, J., Hugdahl, K., & Peterson, B. S. (2006). Hippocampus and amygdala morphology in attention-deficit/hyperactivity disorder. Archives of general psychiatry, 63(7), 795–807. https://doi.org/10.1001/archpsyc.63.7.795

[7] Lanciego, J. L., Luquin, N., & Obeso, J. A. (2012). Functional neuroanatomy of the basal ganglia. Cold Spring Harbor perspectives in medicine, 2(12), a009621. https://doi.org/10.1101/cshperspect.a009621

[8] Rubia K. (2018). Cognitive Neuroscience of Attention Deficit Hyperactivity Disorder (ADHD) and Its Clinical Translation. Frontiers in human neuroscience, 12, 100. https://doi.org/10.3389/fnhum.2018.00100

[9] De La Fuente, A., Xia, S., Branch, C., & Li, X. (2013). A review of attention-deficit/hyperactivity disorder from the perspective of brain networks. Frontiers in Human Neuroscience, 7. https://doi.org/10.3389/fnhum.2013.00192

Larsson H, Asherson P, Chang Z et al.. Genetic and environmental influences on adult attention deficit hyperactivity disorder symptoms: a large Swedish population-based study of twins. Psychol Med. 2013;43(1):197–207. https://doi.org/10.1017/S0033291712001067 Crossref, Medline, Google Scholar

Larsson H, Chang Z, D'Onofrio BM et al.. The heritability of clinically diagnosed attention deficit hyperactivity disorder across the lifespan. Psychol Med. 2014;44(10):2223–2229. https://doi.org/10.1017/S0033291713002493 Crossref, Medline, Google Scholar

Johnson J., Morris S. and George S. (2020) Attention deficit hyperactivity disorder in adults: what the non-specialist needs to know. British Journal of Hospital Medicine 81(3), 1-11. [Abstract] [Free Full-text]