Do ADHD people have difficulty in working memory?

ADHD or attention deficit/hyperactivity disorder is a common neurodevelopmental disorder which means the brain condition affects individuals the whole course of their lives, with a prevalence of 7.2% population as Thomas and colleagues in 2015 did a meta analysis in ADHD prevalence across academic publications. While there was a belief that ADHD is a child disorder and outgrows when they are adults, Franke and colleagues in 2018 contrast that ADHD’s symptoms are persistent and change over the course of their lives. Hyperactivity is dominant when they are young but whey they get older inattention plays a bigger role.

ADHD Criterias

ADHD diagnosis criterias according to DSM-4 or the Diagnostic and Statistical Manual of Mental Disorders version 4 including

1. Inattention is defined by individuals’ inability to give and maintain attention over the course of actions and are easily distracted by unnecessary stimuli or thoughts. They tend to be disorganized which disrupts their work or study. Another sign is being forgetful and losing things in their daily activities.

2. Hyperactivity is recognized by individuals’ incapability to contain ones’ self as expected by others in situations, such as unable to sit peacefully on their seat, often run instead of walk, do not like to be in quiet activities, and talk a lot.

3. Impulsivity is an immediate response toward external stimuli mostly in social situations, such as answering a question before it ends, having a difficult time waiting, and interrupting others in social interactions.

Later in DSM-5 the hyperactivity and impulsivity criterias are grouped together.

As shown above in the inattention criteria individuals with ADHD have a poor ability in memorizing information. There is also research that revealed other factors influencing one’s memory capability, such as reward and feedback processing (2015).

Questions

These bring up questions to be answered:

1. Is working memory tasks’ accuracy different between healthy and ADHD children?
2. Is working memory tasks’ reaction time different between healthy and ADHD children?
3. Is there any interaction effect of working memory and reward amount and feedback time?

These questions, hence, will be answered with open data on the memory of individuals with ADHD.

Dataset and Participants

In 2021, a group of researchers, James R. Booth and his colleagues provided a dataset on OpenNeuro of ADHD children and healthy children who do not have ADHD during working memory tasks with 79 participants.

After the participants with missing data were removed, the descriptive statistics of the dataset is provided. The total number of participants was 54 which 21 participants were diagnosed with ADHD. The average participants’ age is 12.59 years with standard deviation (SD) of 0.93. Regarding the racial profile, around 66% of the children are white American, 22% are Black American, 9% are mixed race, and 2% are Asian American.

Measuring Memory Capability

The implemented task to measure children’s memory was the N-back task. Children were asked to remember English letters on the screen. When the next screen changes to a new letter, they were asked to answer depending on two conditions. The first condition, the spatial working memory task, the children had to answer whether the letter on the current screen was on the same spot as the previous. The second condition, the verbal working memory task, they had to answer whether the letter was the same letter on the previous screen.

There were also other two variations of the N-back task. The first one, reward amount, children were told that pictures of money in the middle of the screen indicated the amount of money they would get if their answers were correct. An image of a big pile of money means they would get 0.25$ and an image of changes they would get 0.02$.

Another variation was feedback time. In the delayed feedback variation, the feedback was given to children in the percentage of correct answers one time at the end of each task. While the immediate feedback variation, if the children gave a correct answer in the consecutive screen showed a green block, and a red block for incorrect answers.

The collected data are ‘accuracy’, the number of correct answers, and ‘reaction time’, the interval between the time when stimuli letters were shown and when the participants gave their responses.

Data Distribution

The data distribution of accuracy and reaction time of healthy and ADHD children are shown in violin plots by task variations. In the accuracy plots, it can be seen that the data are not equally distributed between two groups. While some of reaction time plots are distributed at the same degree.

Findings

In the correlation matrix, there is inconsistency between domains of working memory accuracy where the correlation coefficient between spatial and verbal domains are the lowest among other variations in both groups. While the lowest coefficient is revealed in reward amount’s reaction time. This can be seen as a preliminary investigation of task domains and reward amount on working memory performance.

The group differences are found in working memory accuracy where healthy children show higher working memory performance across all variations. It confirms that ADHD children have poorer working memory compared to healthy children. According to a research in 2011 by Fassbender and colleagues, ADHD children showed a lower level of working memory since they cannot allocate their attention adequately to maintain the presented stimuli. Another explanation was made by Fasco and colleagues in 2020 that their reordering problem, which is inability to maintain and rearrange information, and poor executive function may contribute to the reduced working memory.

The reaction time, however, is revealed to be no significant difference between healthy and ADHD children. While between group accuracy differences are found, reaction time difference is not significant. This observation had been found in a number of studies. A group of researchers led by Tam in 2012 found that intra-individual reaction time variability (VRT) might play a role in the phenomenon. While neuroimages of participants with ADHD were being taken, resting-state activation or noises occurred in a higher ratio than the healthy population. It can be inferred from the violin plot of reaction time that the distribution of ADHD group’s data is wider compared to the healthy group. This aligns with the nature of the ADHD brain activity and results in interference of the measurement outcome.

Finally, there are no interaction effects revealed from the data. Since the interaction between variations of working memory tasks are expected, every combination shows no significant difference. A research team in 2015, Hammer and colleagues, found a similar result on reward amount and feedback combined variation. There was a possibility that the reward-processing brain region might suppress another region that controls the feedback processing region. For example if the reward is big enough to keep children’s attention, they may ignore feedback that comes after.

In the end, it can be concluded that ADHD children have indeed poorer memory than children without ADHD. However, they take the same amount of time as typical children to recognize their memory. With these findings, practitioners, such as psychologists and educators, should give more attention to ADHD children’s working memory in order to improve their cognitive and learning abilities. There is a suggestion for future research to conduct a neuroimaging techniques to study underlying neural connectivity of these working memory variation in depth.

References

Fassbender, C., Schweitzer, J. B., Cortes, C. R., Tagamets, M. A., Windsor, T. A., Reeves, G. M., & Gullapalli, R. (2011). Working memory in attention deficit/hyperactivity disorder is characterized by a lack of specialization of brain function. PloS one, 6(11), e27240.

Franke, B., Michelini, G., Asherson, P., Banaschewski, T., Bilbow, A., Buitelaar, J. K., … & Reif, A. (2018). Live fast, die young? A review on the developmental trajectories of ADHD across the lifespan. European Neuropsychopharmacology, 28(10), 1059–1088.

Fosco, W. D., Kofler, M. J., Groves, N. B., Chan, E. S., & Raiker, J. S. (2020). Which ‘working’ components of working memory aren’t working in youth with ADHD?. Journal of Abnormal Child Psychology, 48, 647–660.

Hammer, R., Tennekoon, M., Cooke, G. E., Gayda, J., Stein, M. A., & Booth, J. R. (2015a). Feedback associated with expectation for larger-reward improves visuospatial working memory performances in children with ADHD. Developmental cognitive Neuroscience, 14, 38–49.

James R. Booth and GE Cooke and Jessica Gayda and Rubi Hammer and Marisa N. Lytle and MA Stein and Michael Tennekoon (2021). Working Memory and Reward in Children with and without Attention Deficit Hyperactivity Disorder (ADHD). OpenNeuro. [Dataset] doi: 10.18112/openneuro.ds002424.v1.2.0

Tamm, L., Narad, M. E., Antonini, T. N., O’Brien, K. M., Hawk, L. W., & Epstein, J. N. (2012). Reaction time variability in ADHD: a review. Neurotherapeutics, 9, 500–508.

Thomas, R., Sanders, S., Doust, J., Beller, E., & Glasziou, P. (2015). Prevalence of attention-deficit/hyperactivity disorder: a systematic review and meta-analysis. Pediatrics, 135(4), e994-e1001.