Published on 13/06/2018 in Sage-Journal of Attention Disorders

The research paper discusses the comorbidity of ADHD and Autism Spectrum Disorder (ASD) and investigates the potential overlap of underlying pathophysiology and endophenotypes between the two disorders.

It highlights the revised diagnostic guidelines allowing for comorbid diagnosis, and the need for more research to understand the nature of the potential overlap. The focus is on examining Intrasubject Variability (ISV) of reaction times (RTs) as an endophenotype, with findings showing elevated ISV in ADHD patients and its relevance in predicting symptoms and responsiveness to treatment. The study also explores other cognitive endophenotypes such as working memory, inhibition, and temporal processing. The paper specifically discusses the inconsistent elevation of ISV across different cognitive tasks in comorbid ASD + ADHD patients compared to pure ASD patients and the need for further investigation to determine the nature of the potential overlap between ASD and ADHD.

Participants

The study included 40 ADHD patients,

• 21 ASD patients without ADHD,
• 19 ASD patients with comorbid ADHD, and
• 40 typically developing controls.

Exclusion criteria comprised severe neurological or psychiatric disorders and intellectual disability. Groups were matched for sex, age, and IQ. Symptom verification for ADHD was conducted using questionnaires. Some patients had a methylphenidate prescription but did not take the medication prior to testing.

Hardware, Tasks, and Procedures

The experiments were conducted using E-Prime 2.0 Professional software and 17-inch monitors. Participants received verbal instructions and practiced with 10 to 20 trials for the tasks.

• The No-Go task (NBT) included 0-Back Task (0BT) and 1-Back Task (1BT), with 25% target trials and the rest nontarget, requiring quick and accurate responses within 0-1,500 ms.
• The Stop Signal Task (SST) had 25% “STOP” trials, where participants needed to inhibit their responses upon seeing a red “STOP” stimulus, with response time recorded between 0-1,650 ms.
• The Temporal Reproduction Task (TRT) involved presenting a white circle for 1, 2, 4, 8, or 16 s, and participants had to reproduce the duration.
• Additionally, Standard Progressive Matrices (R-SPM) for measuring IQ and
• Three other computerized Reaction Time Tasks were administered in a second session. The specific results for these tasks were not included in this report.

Findings

💠They found that patients with ADHD or comorbid ASD+ showed elevated variability in their performance across the tasks and deficits in temporal processing, but none of the groups were impaired in working memory or inhibition.

💠The study also revealed that high levels of variability and generally poor performance in patients with comorbid ASD+ were only partially due to the additive effects of the pure disorders.

💠The findings suggest that variability in reaction times and temporal processing deficits are most sensitive to ADHD symptomatology.

💠The study underscores the importance of considering comorbidity when assessing cognitive processes in autism.

💠These results may help in identifying distinct characteristics of different disorders and inform future treatment approaches

For researchers ⬇️

Is ISV Elevated in ASD Patients?

The study investigated the variability in interstimulus intervals (ISI) for individuals with attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) compared to controls. Results showed that individuals with ASD+ displayed elevated variability in non-speeded behavioral timing (NBT) compared to all other groups, and increased variability in speeded behavioral timing (SST) compared to controls. Additionally, individuals with ADHD demonstrated greater variability in reproduced intervals compared to controls and ASD-patients. Furthermore, significant task-related main effects were observed for the NBT and TRT. Overall, the findings suggest that individuals with ASD+ exhibit elevated variability in ISIs, particularly in non-speeded behavioral timing tasks, compared to both controls and individuals with ADHD.

Are the Levels of ISV Consistent Across Cognitively Heterogeneous Tasks in ASD Patients?

1. The results showed that ADHD patients had significantly elevated ISV compared to controls, while ASD patients performed similarly to controls when working memory (WM) load was increased.
2. The interaction between WM load and group was not significant for most measures, indicating that the increase in WM load did not differentiate the pure disorders from controls.
3. ASD+ patients showed disproportionate alterations in certain measures.
4. In the inhibition task, all groups performed similarly in terms of the accuracy of correctly inhibited responses.
5. The study found differences in ISV between ADHD patients and controls, as well as unique alterations in ASD+ patients, suggesting task-specific patterns of ISV in individuals with neurodevelopmental disorders.

Do Deficits in ASD+ Patients Emerge From Additive or Nonadditive Effects of the Pure Disorders?

1. The results indicate significant nonadditive effects of the pure disorders on the ASD+ group for certain measures.
2. The study suggests that deficits in individuals with both ASD and ADHD emerge from a combination of both additive and nonadditive effects of the pure disorders, depending on the specific cognitive measure.

Overall, the findings highlight the complex interplay between ASD and ADHD symptomatology in contributing to cognitive deficits in ASD+ patients.

Additional Results

The additional results section of the paper examined accuracy and speed measures:

1. The findings revealed a significant interaction between trial type and group for error rates, indicating more errors in ADHD patients than controls for target trials only.
2. The analysis also showed that ASD+ patients omitted more responses than controls following nontarget trials, and task-related main effects were significant for accuracy measures.
3. In terms of response speed, ASD+ patients exhibited significantly longer mean response times compared to all groups, as well as significantly higher variability in response times than controls or ADHD patients.
4. The main effects of load and trial type were also significant for response speed measures, indicating overall differences in speed performance across groups and trial types.

Are Deficits Related to the Selected Candidate Cognitive Endophenotypes of ADHD Found in Patients With ASD?

1. Working Memory load did not differentiate “pure” ADHD or ASD patients from controls, possibly due to the simplicity of the tasks used.
2. ASD+ patients showed disproportionate decreases in response times and increases in omission errors with increased WM load, indicating attention lapses.
3. In terms of inhibitory processing, groups did not differ, possibly due to the unreliability of the measures used.
4. ADHD patients exhibited more incorrect responses and higher temporal error, consistent with previous findings, suggesting a trans-diagnostic marker of ADHD.
5. Temporal processing deficits and elevated intraindividual variability (ISV) exhibited a consistent but partially redundant structure.
6. These findings contribute to the understanding of cognitive endophenotypes in patients with ADHD and ASD and highlight the need for further research to elucidate the underlying processes.