An RCT Of Central Executive Training Vs. Inhibitory Control Training For ADHD

Executive control refers to top-down mental processes like working memory, inhibition, and cognitive flexibility that allow control of thoughts and behaviors. Deficits in these processes are central to ADHD.

Specifically, inhibitory control allows suppressing impulses and responses. Poor inhibitory control, characterized by difficulty inhibiting prepotent responses, is thought to directly cause increased behavioral impulsivity in ADHD.

If a child lacks cognitive control over their motor responses, they will have trouble stopping themselves from interrupting or jumping into an activity without thinking.

Training inhibitory control is thought to be an effective way to target and reduce impulsive behaviors.

Kofler, M. J., Wells, E. L., Singh, L. J., Soto, E. F., Irwin, L. N., Groves, N. B., Chan, E. S. M., Miller, C. E., Richmond, K. P., Schatschneider, C., & Lonigan, C. J (2020). A randomized controlled trial of central executive training (CET) versus inhibitory control training (ICT) for ADHD.  Journal of Consulting and Clinical Psychology, 88(8), 738–756. https://doi.org/10.1037/ccp0000550

Key Points

• The study compared two computerized cognitive training interventions for children with ADHD – central executive training (CET) targeting working memory and inhibitory control training (ICT) targeting inhibition.
• CET demonstrated superiority over ICT for improving working memory, parent-reported ADHD symptoms, teacher-reported ADHD symptoms, and objectively measured hyperactivity.
• There was mixed evidence that ICT improved inhibitory control or transferred to symptom improvements.
• The findings support the continued development of CET but suggest comparison to an active control is needed to evaluate ICT.
• Limitations include unexpected cognitive transfer effects from CET and the lack of a non-executive function control group.

Rationale

Executive function deficits are central to ADHD, but training these abilities has shown little efficacy in past research (Rapport et al., 2013). This could reflect poor targeting – training protocols have not focused specifically on the precise executive functions empirically linked to ADHD behaviors and impairments.

This study continues the development of two new training protocols – CET targets the “working” components of working memory, whereas ICT targets inhibitory control.

Both abilities are implicated in ADHD (Chacko et al., 2014). Comparing them aims to determine their potential efficacy and mechanisms of change.

If improvements in the targeted executive function translate to symptomatic improvements, it would provide a paradigm-shifting approach to treating ADHD’s underlying pathology rather than just managing behavioral symptoms. This moves the field closer to causal models and personalized medicine.

Replicated failures of past executive function training protocols necessitate comparing any new intervention to an adaptive active control training of the other executive function.

Demonstrating unique improvements in the targeted executive function and related behaviors would provide stronger evidence that the training engages its intended mechanism.

Method

Participants were randomized to 10 weeks of CET or ICT.

CET (Central Executive Training):

• Computerized cognitive training intervention targeting working memory
• Involves practicing tasks requiring mental manipulation of information held in short-term/working memory (e.g., reordering numbers/letters, spatial locations)
• Adaptive training that continuously increases difficulty (e.g., by increasing the amount of information to manipulate)
• Delivered via website with game-based working memory tasks and token reinforcement system
• Combined weekly child in-office training with daily parent-supervised training at home

ICT (Inhibitory Control Training):

• Computerized cognitive training intervention targeting inhibitory control
• Involves practicing tasks requiring inhibiting automatic motor responses (action restraint) or stopping ongoing responses (action cancellation)
• Adaptive training that continuously increases difficulty (e.g., by modifying stimulus timing target frequency)
• Delivered via website with game-based inhibition tasks and token reinforcement system
• Combined weekly child in-office training with daily parent-supervised training at home

Dependent variables assessed feasibility, proximal outcomes (working memory, inhibition), and distal outcomes (objective and subjective ADHD symptoms).

Sample

54 children with ADHD ages 8-12. 12 girls, 74% Caucasian. Diagnosed via clinical interview and rating scales. No differences between groups demographically or on pretreatment executive functioning.

Statistical Analysis

Two- and three-way mixed model ANOVAs tested for group by time interactions. Controlling for baseline scores, post-treatment group differences were tested. Bayes factors supplemented p values.

Results

Both treatments showed high feasibility and acceptance.

Parents perceived significant ADHD symptom improvements, especially for CET on the BASC-3 (CET d=0.96-1.42; ICT d=0.45-0.65).

Groups were equivalent on the ADHD-RS-5 (CET d=0.99-1.06; ICT d=0.70-0.94). CET produced superior working memory improvements (d=0.70-0.84), with large effects for CET (d=0.96-1.25) but weaker effects for ICT (d=0.26-0.41).

CET also improved go/no-go inhibition (d=0.47) despite no inhibition training. Stop-signal performance improved for both groups, limiting conclusions.

CET reduced objectively measured hyperactivity during working memory testing (d=0.47), but ICT did not (d=0.17).

CET also showed superior teacher-reported ADHD symptom reductions (d=0.52-0.66).

Formal mediation analyses indicated CET reduced hyperactivity via working memory gains.

Follow-up found CET gains maintained on all measures (d=0.86-1.22), whereas ICT maintained only parent-reported attention improvements (d=0.48-0.56), not hyperactivity (d=0.24-0.42).

Insight

The study provides important advances for ADHD intervention research.

First, CET successfully improved its intended mechanism – working memory. Significant mediation indicates these gains accounted for CET’s behavioral improvements, supporting working memory’s functional role in ADHD.

Second, cognitive and behavioral gains transferred to the classroom, demonstrating real-world benefits detectable even with small samples.

Third, parent-perceived improvements were largely maintained two months after treatment cessation, providing initial evidence that repeated practice may produce lasting gains.

These findings coincide with developmental data suggesting ADHD involves 3-5 year delays in working memory-related neural networks – brief training may provide small “nudges” that accumulate over time.

Conversely, interpreting ICT is complicated by CET, which unexpectedly improves inhibition. This could indicate working memory’s upstream role in inhibition, but comparing ICT to an active control is now vital.

Overall, CET met criteria as a “probably efficacious treatment” for ADHD, whereas determining ICT’s potential requires additional trials.

Both treatments may eventually provide independent or synergistic benefits as part of personalized medicine approaches addressing ADHD’s multi-faceted impairments.

Replicating and extending these initial findings could produce more generalized, pragmatic executive function training protocols that provide patients added access to treatment. Even modest improvements across enough people may have substantial public health impacts.

Strengths

This research has several strengths:

• Triple-blinded randomized controlled methodology is the gold standard for intervention research.
• Additional strengths include concealed unpredictable allocation, blinded data analysis, excluded data under 3.0% meeting MCAR criteria, and preregistered analyses to protect validity.
• Outcomes spanned feasibility, perceived improvement, proximal cognitive targets, distal blind classroom observations, and objectively measured ADHD behaviors.
• Two measures per construct prevented inflated conclusions from measure-specific variance.
• All participants received identical researcher contact, and both training programs featured equivalent adaptive algorithms, game-based formats, and engagement platforms.
• This active control addressed the limitations of the waitlist and non-adaptive comparison groups. Controlling for time actively training addressed intervention intensity differences.
• Stopping rules and power analysis ensured adequate power to detect effects on primary outcomes.

Limitations

There are also some limitations with this research:

• The lack of a non-executive function control group now limits ICT conclusions – inhibition improvements could reflect practice effects, and improvements in objective ADHD behaviors were not detected.
• The unexpected transfer of CET to improved inhibition also limits conclusions regarding ICT’s specificity.
• Generalization is limited demographically, given that only a few girls were included.
• The ADHD sample had high intellectual functioning and few common comorbidities like depression, which can be common in those with ADHD.
• Parent blinding was not possible, given their active participation.
• Although teachers remained blind, some were aware children were receiving intervention.

Implications

Results substantiate executive function training as a promising evidence-based treatment approach for addressing ADHD’s underlying impairments.

Given psychostimulants do not strengthen cortical development and behavior therapies have limited generalization, executive function training that produces lasting neural changes may provide invaluable long-term outcomes.

The cognitive and behavioral improvements evident even with small samples and brief training support the continued optimization of CET.

If ongoing research replicates efficacy over larger, more diverse samples and reveals additive or synergistic benefits with behavior therapy, CET could provide a paradigm-shifting treatment model complementing traditional approaches.

An efficacious executive function training protocol could expand intervention access to the substantial number of families who refuse behavioral treatment and medication. Even modest improvements may have immense public health implications for millions of struggling children.

ICT requires further development but serves the vital purpose of beginning to parse apart shared and distinct treatment mechanisms. For CET, the critical next steps are determining optimal training doses, characterizing responders versus non-responders, and coupling training with biofeedback and/or medications to consolidate neural changes.

Investigating combined or sequential administration will test whether independently improving working memory and inhibition produces additive or synergistic benefits.

Broadly, these interventions represent an important evolution in ADHD precision medicine – continued optimization may soon transition executive function training into standard clinical practice.

References

Primary reference

Kofler, M. J., Wells, E. L., Singh, L. J., Soto, E. F., Irwin, L. N., Groves, N. B., Chan, E. S. M., Miller, C. E., Richmond, K. P., Schatschneider, C., & Lonigan, C. J (2020). A randomized controlled trial of central executive training (CET) versus inhibitory control training (ICT) for ADHD.  Journal of Consulting and Clinical Psychology, 88(8), 738–756. https://doi.org/10.1037/ccp0000550

Other references

Chacko, A., Kofler, M., & Jarrett, M. (2014). Improving outcomes for youth with ADHD: A conceptual framework for combined neurocognitive and skill-based treatment approaches. Clinical Child and Family Psychology Review, 17(4), 368–384. https://doi.org/10.1007/s10567-014-0171-5

Rapport, M. D., Orban, S. A., Kofler, M. J., & Friedman, L. M. (2013). Do programs designed to train working memory, other executive functions, and attention benefit children with ADHD? A meta-analytic review of cognitive, academic, and behavioral outcomes. Clinical Psychology Review, 33(8), 1237–1252. https://doi.org/10.1016/j.cpr.2013.08.005

Shaw, P., Eckstrand, K., Sharp, W., Blumenthal, J., Lerch, J. P., Greenstein, D. E., Clasen, L., Evans, A., Giedd, J., & Rapoport, J. L. (2007). Attention-deficit/hyperactivity disorder is characterized by a delay in cortical maturation. Proceedings of the National Academy of Sciences, 104(49), 19649-19654. https://doi.org/10.1073/pnas.0707741104

Simons, D. J., Boot, W. R., Charness, N., Gathercole, S. E., Chabris, C. F., Hambrick, D. Z., & Stine-Morrow, E. A. (2016). Do “brain-training” programs work?. Psychological Science in the Public Interest, 17(3), 103-186. https://doi.org/10.1177%2F1529100616661983

Keep Learning

Here are some suggested Socratic questions for students to critically analyze and discuss this research paper further:

1. What are the advantages and disadvantages of using computerized cognitive training interventions compared to traditional behavioral interventions or medications?
2. How might we determine the optimal “dosage” of executive function training needed to produce lasting neural and behavioral change in ADHD?
3. What participant characteristics or comorbid disorders might influence or moderate response to executive function training protocols?
4. How can technology be leveraged to increase accessibility and dissemination of evidence-based executive function training programs?
5. What ethical considerations should guide the collection, analysis, and application of genetic or neurological data used to personalize executive function training protocols?