Week 11: ADHD & OCD

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Quiz

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Learning Objectives

By the end of this lesson, students will be able to:

Differentiate between ADHD and OCD based on underlying brain mechanisms rather than surface-level behaviors
Explain how attention difficulties can arise from different causes, including attention dysregulation versus anxiety-driven intrusive thoughts
Compare and contrast key symptoms of ADHD and OCD using real-world examples
Describe the neurobiological similarities and differences between ADHD and OCD, including brain circuits and neurotransmitters
Identify how ADHD and OCD may co-occur and interact in daily functioning
Evaluate why accurate diagnosis is important for effective treatment and support strategies
Apply knowledge of ADHD and OCD to distinguish between distractibility and anxiety-driven behaviors in case scenarios

ADHD vs. OCD: Why They Can Look Similar (But Are Different)

(Brem et al., 2014; American Psychiatric Association [APA], 2022) (Brem et al., 2014)

Sometimes people say things like, “I can’t focus on work or school—do I have ADHD?” However, focusing difficulty is not always caused by ADHD. In some cases, it may be related to obsessive-compulsive disorder (OCD). Although ADHD and OCD are very different conditions, they can sometimes look similar from the outside, which may lead to confusion or misdiagnosis.

Both ADHD and OCD can involve similar outward signs, such as trouble concentrating, difficulty finishing tasks, restlessness, and repetitive behaviors. However, the reason these symptoms occur is very different. Understanding the underlying cause is important because the two conditions involve different brain systems and often require different treatment approaches.

Two Different “Engines” in the Brain

(APA, 2022; Barkley, 2015) (Brem et al., 2014)

One helpful way to understand the difference between ADHD and OCD is to think about the “engine” driving the behavior. ADHD is primarily driven by problems with attention regulation, executive functioning, and impulse control. The brain has difficulty managing focus, resisting distractions, organizing behavior, and sustaining effort on tasks that are not highly stimulating. People with ADHD are often pulled away from tasks by boredom, environmental distractions, or new stimuli.

OCD, in contrast, is driven by anxiety and intrusive thoughts. People with OCD often become stuck on distressing thoughts, urges, or mental images and feel compelled to perform repetitive behaviors or mental rituals in order to reduce anxiety or prevent a feared outcom. In simple terms, ADHD involves difficulty regulating attention and impulses, whereas OCD involves difficulty managing anxiety and intrusive thoughts.

How the Symptoms Can Look Similar

(APA, 2022; Cleveland Clinic, 2023) (Brem et al., 2014) (APA, 2022) (Brem et al., 2014) (Barkley, 2015)

At first glance, some behaviors in ADHD and OCD may appear alike, even though their causes are very different.

Difficulty Focusing

In ADHD, attention often drifts because the brain seeks stimulation and is easily distracted by other thoughts, sounds, or activities. Individuals may have difficulty sustaining attention on tasks that feel repetitive, uninteresting, or mentally demanding. In OCD, attention may also be disrupted, but for a different reason: it is pulled away by obsessive thoughts, doubts, or fears that are difficult to ignore.

Repetitive Behaviors

Repetitive behaviors may also appear similar across the two conditions. In ADHD, behaviors such as tapping, pacing, fidgeting, or shifting positions are often related to restlessness, hyperactivity, or excess mental and physical energy. In OCD, however, repetitive behaviors such as checking, counting, arranging, cleaning, or mentally repeating phrases are compulsions performed to reduce anxiety or prevent something feared from happening.

Forgetfulness

Forgetfulness can also look similar, but it often comes from different mechanisms. In ADHD, forgetfulness is commonly linked to working-memory challenges, distractibility, and disorganization. In OCD, memory may feel unreliable because repeated checking creates doubt, making the person feel unsure whether something was already completed correctly.

Key Characteristics of ADHD

(APA, 2022) (Cleveland Clinic, 2023) (Faraone et al., 2005; Faraone et al., 2015; Polanczyk et al., 2007) (APA, 2022; National Institute of Mental Health [NIMH], 2024) (Barkley, 2015) (NIMH, 2024)

Attention-Deficit/Hyperactivity Disorder (ADHD) is a neurodevelopmental condition that affects attention regulation, impulse control, and activity levels. Rather than representing a lack of attention, ADHD reflects difficulty directing, sustaining, and regulating attention in a flexible and goal-directed way. Many individuals with ADHD struggle to focus on tasks that require sustained mental effort, resist distractions, stay organized, or control impulsive behavior. At the same time, some individuals may experience “hyperfocus” during activities that are highly stimulating or personally interesting.

ADHD symptoms typically begin in childhood, often between ages three and six, and must be present before age 12 for diagnosis. Symptoms must also occur in more than one setting, such as home, school, or work. ADHD is one of the most common neurodevelopmental disorders, affecting approximately 5–10% of children worldwide, and many individuals continue to experience symptoms into adulthood.

Common patterns seen in ADHD include:

Lifelong difficulty sustaining attention
Losing items or forgetting tasks
Procrastination or difficulty starting tasks
Impulsivity or interrupting others
Disorganization and inconsistent routines

People with ADHD often describe having a “busy mind” that jumps quickly from one idea to another.

Core Symptom Domains of ADHD

ADHD symptoms are generally grouped into two main domains: inattention and hyperactivity/impulsivity. Inattention symptoms include difficulty sustaining attention, organizing tasks, following through on instructions, and completing activities that require prolonged mental effort. Individuals may frequently lose items, become distracted by external events or internal thoughts, and appear forgetful in daily life.

Hyperactivity and impulsivity symptoms may include excessive movement, restlessness, difficulty sitting still, talking excessively, interrupting others, or acting before thinking through consequences. These behaviors are often linked to problems with inhibitory control and self-regulation.

Types of ADHD

Clinicians identify several presentations of ADHD depending on which symptoms are most prominent:

Predominantly Inattentive Presentation – difficulty sustaining attention, organizing tasks, and completing work, with fewer hyperactive symptoms
Predominantly Hyperactive-Impulsive Presentation – excessive movement, impulsive behavior, and difficulty remaining still
Combined Presentation – significant symptoms from both categories
Unspecified Presentation – symptoms cause impairment but do not fully fit one of the other presentations

Clinicians may also describe ADHD as mild, moderate, or severe depending on how much symptoms interfere with daily functioning.

Recognizing ADHD in Adults

Many adults with ADHD are unaware they have the condition and may instead feel that everyday tasks are unusually difficult to manage. They may experience chronic problems with attention, organization, planning, and impulse control without realizing these challenges reflect an underlying neurodevelopmental condition. Adults with ADHD may have trouble prioritizing responsibilities, completing projects on time, keeping track of appointments, or maintaining routines.

Impulsivity can also affect adult functioning. Adults with ADHD may struggle with impatience, interrupting conversations, making quick decisions, emotional reactivity, and difficulty tolerating frustration.

Common symptoms of ADHD in adulthood include:

Impulsiveness and difficulty controlling reactions
Disorganization and trouble prioritizing tasks
Poor time management and missed deadlines
Difficulty focusing or sustaining attention
Problems multitasking or switching effectively between tasks
Restlessness or excessive mental activity
Poor planning and difficulty completing long-term projects
Low frustration tolerance
Frequent mood changes
Difficulty following through on commitments
Irritability or a “short temper”
Trouble coping with stress

It is important to recognize that many people occasionally experience distraction or forgetfulness, but ADHD is diagnosed only when symptoms are persistent, present across settings, and significantly interfere with daily functioning. Symptoms must also have been present in childhood, even if they were not formally recognized at the time.

Living With ADHD in Adulthood: Challenges and Self-Management Strategies

(APA, 2022; NIMH, 2024)(Barkley, 2015; NIMH, 2024)

ADHD symptoms often change across the lifespan. While hyperactivity in childhood may become less visible in adulthood, it may be replaced by internal restlessness, difficulty relaxing, or a constant sense of mental activity. The demands of adult life—such as work, finances, relationships, and household responsibilities—can make ADHD symptoms more noticeable or disruptive.

Adults with ADHD frequently experience difficulties with sustained attention, organization, task completion, emotional regulation, and follow-through. Tasks that require long periods of effort, such as paperwork, budgeting, planning, or completing long-term projects, may feel especially difficult unless they are highly engaging.

Common difficulties experienced by adults with ADHD include:

Managing and sustaining attention
Completing long or complex tasks unless highly interesting
Organizing daily responsibilities and reducing clutter
Controlling impulsive behavior
Maintaining emotional regulation and managing frustration

Although ADHD can create significant challenges, many adults learn effective self-management strategies. Helpful supports may include:

Breaking large tasks into smaller steps
Using planners, alarms, and digital reminders
Creating structured routines and external organization systems
Practicing stress management and mindfulness
Maintaining healthy habits such as regular exercise, sufficient sleep, and balanced nutrition

ADHD is not a sign of laziness or low intelligence. It is a neurodevelopmental condition that affects executive functioning, attention regulation, impulse control, and planning. With proper support, many individuals with ADHD function very well and may also show strengths such as creativity, high energy, and strong focus on areas of interest.

What Is OCD?

(Brem et al., 2014) (APA, 2022; Brem et al., 2014)

Obsessive-Compulsive Disorder (OCD) is a long-lasting mental health condition characterized by a cycle of obsessions and compulsions that cause distress and interfere with daily life. Obsessions are unwanted, intrusive thoughts, urges, or mental images that create anxiety. Compulsions are repetitive behaviors or mental rituals performed to reduce that anxiety or prevent a feared event.

People with OCD often feel driven to perform compulsions even when they recognize that the behavior may not make logical sense. This creates a repeating cycle:

Intrusive thought → Anxiety → Compulsive behavior → Temporary relief → Thought returns

Examples of Common Obsessions

Fear of contamination, germs, or illness
Perfectionism or a need for symmetry
Religious or moral concerns
Doubts about relationships
Fear of being responsible for something bad happening

Examples of Common Compulsions

Excessive washing or cleaning
Repeated checking of locks, appliances, or safety concerns
Arranging objects until they feel “just right”
Repeating actions, words, or prayers
Mental rituals such as counting or repeating phrases
Seeking reassurance from others

Compulsions may temporarily reduce anxiety, but they tend to strengthen the OCD cycle over time.

Key Features of OCD

Obsessions and compulsions can consume significant time and energy
Symptoms may come and go or change in intensity
Stress often makes symptoms worse
Symptoms can interfere with work, school, relationships, and daily functioning
Compulsions usually provide only short-term relief

OCD symptoms often begin between late childhood and young adulthood, and many individuals with OCD also experience co-occurring anxiety, depression, or tic-related symptoms.

When ADHD and OCD Occur Together

It is possible for someone to have both ADHD and OCD. Research suggests that a notable percentage of people with OCD also meet criteria for ADHD, which means the two conditions can co-occur and interact in meaningful ways.

When both conditions occur together, symptoms may become more complicated. For example:

ADHD impulsivity may trigger intrusive thoughts
ADHD difficulty shifting attention may make it harder to disengage from obsessive thinking
OCD rituals may consume time and further disrupt attention and productivity

Because ADHD and OCD can overlap behaviorally while differing in cause, a careful evaluation by a trained clinician is often necessary to clarify what is happening and determine the best treatment approach.

Why This Matters

(Barkley, 2015; Faraone et al., 2015) (Brem et al., 2014)

Understanding the difference between ADHD and OCD is important because the treatments are very different. ADHD interventions often focus on improving attention regulation, executive functioning, behavior management, and sometimes medication that targets dopamine and norepinephrine systems. OCD treatment, in contrast, often focuses on reducing anxiety and breaking the obsession-compulsion cycle, commonly through exposure-based therapy and medications that target serotonin systems.

Recognizing the underlying cause of attention problems helps people receive the most appropriate support, strategies, and treatment for their specific needs.

The Neurobiological Link Between ADHD and OCD

Although ADHD and OCD are different conditions, research suggests they share some overlap in the brain's systems involved in attention, self-control, and behavior regulation. Both conditions are linked to dysfunction in cortico-striato-thalamo-cortical (CST) circuits, which are brain networks that regulate attention, inhibition, error monitoring, planning, and goal-directed behavior (Brem et al., 2014). These circuits connect key regions such as the prefrontal cortex, anterior cingulate cortex (ACC), basal ganglia, and thalamus.

What is especially interesting is that ADHD and OCD may involve some of the same brain networks, but in different ways. In ADHD, researchers often find under activation in systems responsible for inhibition, sustained attention, and executive control. This helps explain distractibility, impulsiveness, inconsistent follow-through, and difficulty regulating behavior. In OCD, some of these same systems may become overactive, especially those involved in performance monitoring and error detection. This may help explain why people with OCD can feel that something is “not right,” become stuck in doubt, and feel driven to repeat behaviors or mental rituals until anxiety decreases (Brem et al., 2014).

One especially important brain region in both disorders is the anterior cingulate cortex (ACC). The ACC plays a central role in detecting conflict, monitoring errors, and signaling when behavior needs adjustment. In OCD, the ACC may be overactive, contributing to excessive doubt, checking, and the uncomfortable feeling that something has not been completed correctly. In ADHD, however, the ACC often shows reduced activation, which is associated with weaker error monitoring, poorer inhibition, and greater impulsivity (Brem et al., 2014). In this way, both conditions affect self-regulation, but one may reflect under-breaking while the other reflects over-signaling of error or threat.

Science writer David Adam has obsessive compulsive disorder (OCD). In the first of a series of films, he meets Professor Trevor Robbins, Head of Psychology at the University of Cambridge, to find out what we know about OCD and how scientists study the condition.

This animation has been created as part of the OCD and the Brain project.

What Brain Imaging Shows in OCD

One question people sometimes ask is whether a brain scan can help diagnose OCD or guide treatment. This is a common and understandable question—especially since research has shown that OCD was one of the first psychiatric conditions where brain imaging revealed consistent differences in brain activity (Baxter et al., 1987; Pittenger, n.d.).

Early studies using PET scans found that certain brain regions in individuals with OCD show higher levels of activity, even when the person is at rest. The most consistently involved areas include:

Orbitofrontal cortex (OFC) – involved in decision-making, evaluating risk, and detecting when something feels “wrong”
Basal ganglia (including the caudate nucleus) – involved in habit formation and behavior regulation
Anterior cingulate cortex (ACC) – involved in error detection and conflict monitoring
Thalamus – helps relay and regulate information between brain regions

These areas are part of a loop known as the cortico-striato-thalamo-cortical (CST) circuit, which plays a key role in regulating thoughts and behaviors. In OCD, this circuit appears to become overactive, almost like a feedback loop that cannot shut off properly. This may help explain why intrusive thoughts feel persistent and why individuals feel compelled to repeat behaviors (Brem et al., 2014; Pittenger, n.d.).

Research using fMRI has further shown that activity in these regions often increases when OCD symptoms are triggered, such as when a person is exposed to something that provokes their fears. In addition, higher levels of activity in these circuits are often associated with greater symptom severity and may decrease when treatment is effective (Brem et al., 2014).

Jonathan Grayson, PhD, talks about obsessive-compulsive disorder (OCD) and its effects associated with the brain. OCD has two components: learning and biological. OCD sufferers want to be 100% certain and satisfied.

Jonathan Grayson, PhD, talks about the biology of obsessive compulsive disorder (OCD). OCD is not only a learning disorder, but also a biological disorder. It is difficult to point out whether a sufferer is going through the learning aspect or biological aspect.

Why Brain Scans Are Not Used for Diagnosis

Even though research clearly shows differences in brain activity in OCD, brain scans are not currently used to diagnose OCD in individuals. This is because brain imaging findings are based on group-level differences, not precise individual predictions (Pittenger, n.d.).

In other words, while people with OCD may show patterns of increased activity in certain brain regions on average, these differences are not specific enough to reliably determine whether a single individual has OCD. In fact, many individuals with OCD may have brain scans that appear completely normal.

A helpful way to think about this is through an analogy: there may be a general relationship between two variables, such as height and sex, but knowing one does not allow us to accurately predict the other in every individual case. Similarly, although certain brain patterns are associated with OCD, they are not accurate enough to serve as a diagnostic tool (Pittenger, n.d.).

Key Takeaway

(Barkley, 2015; Faraone et al., 2015) (Volkow et al., 2009) (del Campo et al., 2011) (Brem et al., 2014; APA, 2022) (Rubia, 2018) (De La Fuente et al., 2013) (Lanciego et al., 2012) (Plessen et al., 2006) (Gehricke et al., 2017; Shaw et al., 2007)

Brain imaging has been incredibly valuable for understanding the neuroscience of OCD, especially the role of overactive circuits involving the orbitofrontal cortex, basal ganglia, and related regions. However, these tools are currently used for research purposes, not for diagnosis or treatment planning in clinical practice.

At this time, the most reliable way to diagnose OCD remains a comprehensive clinical assessment, including understanding a person’s thoughts, behaviors, and experiences.

Neurochemical and Genetic Differences

Researchers have also identified neurochemical differences between the two conditions. ADHD is more strongly associated with dysregulation in dopamine and norepinephrine systems, which helps explain why stimulant and non-stimulant ADHD medications often target these neurotransmitters. OCD, in contrast, has been more strongly associated with serotonin, and in some cases glutamate, which aligns with the use of SSRIs and exposure-based therapy in treatment.

At the genetic level, both ADHD and OCD are highly heritable, meaning biology plays an important role in risk. Brem and colleagues (2014) note that some genetic findings suggest overlapping vulnerability, while others point to important differences. This supports the view that ADHD and OCD are neither completely unrelated nor identical; rather, they are distinct disorders with partial overlap in brain circuitry, cognition, and inherited risk.

Overall, research suggests that ADHD and OCD may lie on different ends of an impulsive-compulsive spectrum. ADHD is more often associated with disinhibition, impulsivity, and variable attention, whereas OCD is more often associated with overcontrol, compulsive repetition, and distress-driven rigidity. Even so, both conditions can disrupt executive functioning, interfere with daily life, and sometimes occur together.

Brain Structure and Function in ADHD

Research shows that the ADHD brain differs from a neurotypical brain in both structure and function, particularly in areas involved in attention, motivation, and self-regulation. One of the most important differences involves neurotransmitters, especially dopamine and norepinephrine. These two chemical messengers work closely together, and lower levels or dysregulation of both have been strongly linked to ADHD symptoms such as inattention, impulsivity, and difficulty sustaining effort.

Dopamine plays a key role in the brain’s reward system, helping us stay motivated and engaged. In ADHD, disruptions in dopamine signaling may change how the brain experiences reward and pleasure. This can make it harder to stay focused on tasks that feel boring, repetitive, or have delayed rewards, while making highly stimulating tasks easier to engage with.

Norepinephrine, also called noradrenaline, is especially important in the prefrontal cortex, the area of the brain responsible for attention, planning, and self-control. When norepinephrine signaling is disrupted, it can become more difficult to hold information in mind, stay organized, and resist distractions.

Key Brain Regions Involved in ADHD

Several brain regions show structural or functional differences in individuals with ADHD:

Frontal Cortex (Prefrontal Cortex)

Responsible for attention, planning, impulse control, and decision-making
Often shows delayed maturation or reduced activity in ADHD
This helps explain difficulties with focus, organization, and self-regulation

Limbic System (Emotion and Motivation)

Includes structures like the amygdala and hippocampus
Plays a role in emotional regulation and motivation
Differences in this system may contribute to impulsivity, emotional reactivity, and difficulty with decision-making

Basal Ganglia

Involved in motor control, habit learning, and behavior regulation
Helps with planning, focus, and multitasking
Differences in this region may affect movement, attention, and goal-directed behavior

Brain Networks and Attention

The brain works through networks of neurons that communicate using chemical signals. In ADHD, these brain networks may be less efficient, particularly those involved in attention and executive functioning.

Research suggests that differences in these networks can affect the ability to:

Organize and prioritize tasks
Maintain focus
Follow instructions
Work toward long-term goals

In addition, the connection between the prefrontal cortex and other brain regions may be weaker or less coordinated in ADHD. This may contribute to distractibility, impulsivity, and difficulty with planning and memory.

Brain Networks and Attention

Research suggests that differences in these networks can affect the ability to:

Organize and prioritize tasks
Maintain focus
Follow instructions
Work toward long-term goals

The Default Mode Network (DMN)

Another important difference involves the default mode network (DMN). This network becomes active when the brain is at rest, such as during daydreaming or mind-wandering.

In ADHD, the DMN may be more active than usual, even when a person is trying to focus on a task. This can cause attention to shift away from the task toward unrelated thoughts, which helps explain why staying focused—especially on repetitive or uninteresting tasks—can feel particularly difficult.

Key Takeaway: The ADHD Brain Is Wired Differently

Overall, ADHD is not a lack of effort or motivation—it reflects real differences in how the brain is structured and how it functions. Differences in brain regions, networks, and neurotransmitters all contribute to challenges with attention, planning, impulse control, and emotional regulation.

These differences also help explain why individuals with ADHD may:

Struggle with long-term or low-reward tasks
Prefer immediate rewards over delayed ones
Experience difficulty with organization and follow-through
Feel mentally restless or easily distracted

Understanding the brain basis of ADHD helps reduce stigma and supports more effective strategies, treatment, and self-compassion.

Final Takeaway

ADHD and OCD may look similar on the surface, but they are driven by different underlying processes. ADHD is more closely related to distractibility, impulse control difficulties, and under-regulation of attention, whereas OCD is more closely related to anxiety, intrusive thoughts, compulsive rituals, and overcontrol. Because outward behavior alone can be misleading, careful assessment is essential. Understanding the true “engine” behind the symptoms helps guide accurate diagnosis, effective treatment, and better long-term support.

References

American Psychiatric Association. (2022). Diagnostic and statistical manual of mental disorders (5th ed., text rev.; DSM-5-TR).

Barkley, R. A. (2015). Attention-deficit hyperactivity disorder: A handbook for diagnosis and treatment (4th ed.). Guilford Press.

Baxter, L. R., Jr., et al. (1987). Caudate glucose metabolic rate changes with both drug and behavior therapy for obsessive-compulsive disorder. Archives of General Psychiatry, 44(3), 211–218.

Brem, S., Grünblatt, E., Drechsler, R., Riederer, P., & Walitza, S. (2014). The neurobiological link between OCD and ADHD. Attention Deficit and Hyperactivity Disorders, 6(3), 175–202. https://doi.org/10.1007/s12402-014-0146-x

Cleveland Clinic. (2023). Attention-deficit/hyperactivity disorder (ADHD). https://my.clevelandclinic.org

De La Fuente, A., et al. (2013). ADHD from the perspective of brain networks. Frontiers in Human Neuroscience, 7.

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

Faraone, S. V., et al. (2005). The worldwide prevalence of ADHD. Biological Psychiatry, 57(11), 1313–1323.

Faraone, S. V., et al. (2015). Attention-deficit/hyperactivity disorder. Nature Reviews Disease Primers, 1, 15020.

Gehricke, J. G., et al. (2017). The brain anatomy of ADHD in young adults. PLOS ONE, 12(4), e0175433.

Lanciego, J. L., et al. (2012). Functional neuroanatomy of the basal ganglia. Cold Spring Harbor Perspectives in Medicine, 2(12), a009621.

National Institute of Mental Health. (2024). Attention-deficit/hyperactivity disorder. https://www.nimh.nih.gov

Pittenger, C. (n.d.). Should I get a brain scan for OCD? Yale School of Medicine.

Plessen, K. J., et al. (2006). Hippocampus and amygdala morphology in ADHD. Archives of General Psychiatry, 63(7), 795–807.

Polanczyk, G., et al. (2007). The worldwide prevalence of ADHD: A systematic review and meta-regression analysis. American Journal of Psychiatry, 164(6), 942–948.

Rubia, K. (2018). Cognitive neuroscience of ADHD. Frontiers in Human Neuroscience, 12, 100.

Shaw, P., et al. (2007). Attention-deficit/hyperactivity disorder is characterized by a delay in cortical maturation. Proceedings of the National Academy of Sciences, 104(49), 19649–19654.

Volkow, N. D., et al. (2009). Evaluating dopamine reward pathway in ADHD: Clinical implications. JAMA, 302(10), 1084–1091. https://doi.org/10.1001/jama.2009.1308

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