Attention-deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterized by inattention, hyperactivity and impulsivity. One of the hallmark symptoms of ADHD is difficulty with working memory – the ability to temporarily hold and manipulate information in the mind. But does every person with ADHD struggle with working memory? Let’s take a closer look.
What is working memory?
Working memory is a key cognitive function that allows us to briefly hold information in mind while performing complex tasks. It acts as mental “scratchpad” that lets us store and manipulate information for brief periods of time. Working memory has several key components:
- Phonological loop – stores speech-based information
- Visuospatial sketchpad – stores visual and spatial information
- Episodic buffer – integrates information from phonological loop and visuospatial sketchpad with long-term memory
- Central executive – oversees and controls the flow of information
Working memory is essential for many everyday tasks like having a conversation, reading comprehension, performing mental calculations, following directions and multitasking. People with strong working memory can juggle multiple pieces of transitory information simultaneously.
The link between ADHD and working memory
A significant body of research has established a connection between ADHD and working memory deficits. Some key findings include:
- 30-50% of children with ADHD have impaired verbal working memory.
- Deficits in visuospatial working memory are also common.
- The central executive component of working memory appears to be particularly affected.
- ADHD is linked to abnormalities in prefrontal brain regions that support working memory.
In one study, researchers gave children with and without ADHD a series of verbal and visuospatial working memory tasks. The ADHD group performed worse than controls on almost all measures. They had poorer abilities to store, manipulate and recall information over short periods of time.
Brain imaging studies also show that people with ADHD have altered structure and function in prefrontal regions like the dorsolateral prefrontal cortex. These areas play a major role in holding working memory contents online.
Do all people with ADHD have impaired working memory?
While ADHD and working memory deficits are clearly linked, not every person with ADHD has significant impairment. Estimates vary, but research suggests:
- 30-50% of children with ADHD have verbal working memory deficits
- 25-40% have visuospatial working memory deficits
So while a large proportion of people with ADHD struggle with working memory, it does not appear to be a universal feature of the disorder. Some individuals with ADHD have normal or even superior working memory abilities.
For example, one study tracked working memory development in children with and without ADHD over several years. While the ADHD group started out with poorer performance, around 19% had normal working memory capabilities that were on par with their non-ADHD peers by age 16.
Key factors that influence working memory in ADHD
An individual’s specific type of ADHD and other cognitive strengths and weaknesses contribute to whether working memory problems are present. Key factors include:
ADHD presentation
There are three main presentations of ADHD:
- Inattentive (difficulty focusing)
- Hyperactive/impulsive (excess activity and impulsiveness)
- Combined (inattention and hyperactivity/impulsivity)
Research indicates the inattentive presentation is most closely associated with working memory deficits. People with this ADHD type rely heavily on working memory to sustain focus, so impairments are very disabling.
In contrast, those with the hyperactive/impulsive form are less likely to have verbal and visuospatial working memory deficits. But they may still struggle with the central executive component of working memory. This can make it hard to control impulses and think before acting.
IQ and learning disabilities
Individuals with ADHD and normal intelligence (IQ scores around 85 and above) are less likely to have severe working memory deficits. However, problems emerge when ADHD is paired with a learning disability or low IQ below 85.
For example, over 50% of kids with ADHD and a learning disability like dyslexia experience verbal working memory deficits. Adults with ADHD and low IQ also report more significant functional impairments in working memory that impact their daily lives.
Age
Working memory and executive functions mature gradually over childhood and adolescence. As a result, severe working memory deficits in ADHD may improve by adulthood. Up to 19% of children with ADHD and poor working memory will catch up to normal levels by their teenage years.
Gender
Some research indicates females with ADHD may have greater verbal working memory impairments compared to males. But findings are mixed, and other studies show no gender differences.
How is working memory assessed in ADHD?
Since working memory is not universally impaired in all people with ADHD, thorough assessment is important. Some ways clinicians and researchers evaluate working memory include:
Neuropsychological testing
Comprehensive neuropsychological evaluations are considered the gold standard for assessing working memory and executive functions. They involve paper-and-pencil and computerized tests like:
- Digit span (recalling sequences of numbers forwards and backwards)
- Letter-number sequencing (recalling mixed letters and numbers in order)
- Spatial span (recalling sequences of tapping spatial locations)
- N-back task (identifying when a current stimulus matches one from n steps earlier)
- Keep Track (constantly updating items held in memory while processing new info)
These provide objective measures of verbal, visuospatial and executive working memory abilities.
Behavior rating scales
Checklists filled out by parents, teachers and the individual can also assess working memory struggles in everyday life. For example:
- ADHD rating scales include working memory items like “forgetful in daily activities”, “difficulty following instructions” and “loses track of tasks”
- BRIEF rating scale includes working memory items like “when given three things to do, remembers only the first or last”
These capture functional impairments that formal testing may miss.
Self-report measures
Self-reports can provide information on an individual’s subjective working memory abilities. For example:
- The Cognitive Failures Questionnaire includes items about absentmindedness like “Do you fail to notice signposts on the road?”
- The Barkley Deficits in Executive Functioning Scale assesses real-world working memory impairments.
Brain imaging
Functional MRI scans can reveal how well working memory brain networks activate during memory tasks. People with ADHD show weaker activation in key regions like the prefrontal cortex.
Treatment implications
Determining if a person with ADHD has clinically significant working memory deficits has important treatment implications:
Medication
Stimulant medications like methylphenidate and amphetamines may improve working memory in some people with ADHD. Effects tend to be greatest for the central executive aspect of working memory.
Cognitive training
Directly training working memory with computerized programs and exercises can yield functional improvements for those with deficits. Virtual reality training also shows promise for generalizing benefits to daily life.
Classroom accommodations
Students with ADHD and poor working memory may benefit from classroom accommodations like:
- Reducing distractions
- Providing written/visual aids
- Allowing note-taking
- Offering additional time and repetition
These compensate for difficulties with storing and manipulating information.
Compensatory strategies
Adults with ADHD can learn to compensate for working memory deficits by using external aids like planners, notes, alarms and keeping clutter to a minimum. This circumvents reliance on internally holding information.
Conclusion
In summary, working memory deficits are common in ADHD but not universal. While many people with ADHD struggle to hold and manipulate information in-the-moment, others retain normal working memory abilities. Careful clinical assessment provides valuable insights for diagnosis and guiding appropriate, personalized treatment.