Does training working memory or inhibitory control produce far-transfer improvements in set shifting for children with ADHD? A randomized controlled trial

ABSTRACT

Children with ADHD show impairments in set shifting task performance. However, the limited available evidence suggests that directly training shifting may not improve shifting performance in this population. We hypothesized that this incongruence may be because impairments exhibited by children with ADHD during shifting tasks are due to deficits in other executive functions, as shifting tasks also engage children’s working memory and/or inhibitory control abilities. This randomized controlled trial examined the extent to which neurocognitive training of working memory vs. inhibitory control can produce downstream (far-transfer) improvements in set shifting task performance. Children with ADHD ages 8–12 (M = 10.41, SD = 1.46; 12 girls; 74% White/Non-Hispanic) were randomized to either central executive training (CET; n = 25) or inhibitory control training (ICT; n = 29), two next-generation digital therapeutics previously shown to improve their intended neurocognitive targets. Two criterion set shifting tests were administered at pre- and post-treatment. Results indicated that ICT was superior to CET for improving shifting accuracy (treatmentxtime: p = .03, BF₁₀ = 3.01, η² = .09, d = 0.63). ICT was also superior to CET for improving shifting speed, albeit on only one of the two outcome tasks (p = .02, BF₁₀ = 4.53, η² = .08, d = 0.59). CET did not produce improvements in shifting speed or accuracy on either task (p > .52, BF₀₁ > 2.62), but showed evidence for more general (non-shifting-specific) improvement in response times on one of the outcome tasks (shift trials, d = 0.70; non-shift trials, d = 0.68). Taken together, these findings confirm that inhibitory control is important for successful performance on shifting tests, and suggest that training inhibitory control may reflect a method for improving set shifting difficulties in children with ADHD.

KEYWORDS:

• ADHD
• set shifting
• inhibitory control
• working memory
• randomized controlled trial

Study timeline, randomization, unpredictable allocation concealment, masking, and open science disclosure statement

The sample reflects consecutive referrals from March 2017 to March 2019 who were included in the Kofler et al. (2020) randomized controlled trial. Intervention effects on the study’s primary outcomes (working memory, inhibitory control, ADHD symptoms) are reported in Kofler et al. (2020); academic outcomes are reported in Singh et al. (2022). Randomization was conducted by the study methodologist using unpredictable allocation stratified by medication status according to CONSORT guidelines. Study evaluators were masked to treatment group. Data screening, cleaning, and analyses were conducted masked to treatment group/target. We report how we determined our sample size, all data exclusions, all manipulations, and all measures in the study.

Disclosure statement

Michael Kofler/Florida State University (FSU) was awarded U.S. Patent 11,210,967 for the neurocognitive interventions described in the present study. Central Executive Training was recently licensed to Sky Therapeutics, with whom Michael Kofler is in negotiations to serve as Chief Science Officer and consultant. There are no other financial or other conflicts to report.

Supplementary material

Supplemental data for this article can be accessed at https://doi.org/10.1080/09297049.2022.2138301

Notes

¹ Set shifting training has also been studied in college students with ADHD, but its efficacy is uncertain because the authors did not report whether set shifting improved following training (White & Shah, 2006). Instead, the study focused on changes in mixing costs (performance on shifting tasks that alternate between two simple decision tasks relative to performance when completing each of the two simple decision tasks separately), which have been shown to reflect other higher-order cognitive processes rather than set shifting per se (e.g., Pereg et al., 2013). Notably, the college ADHD study found that set shifting training produced significantly greater reductions in mixing cost speed for the set shifting training relative to a no-contact control group (White & Shah, 2006). (Kray et al., 2012) and Pereg et al. (2013) also reported significantly reduced mixing costs for shifting training relative to active control conditions in neurotypical samples, but this effect failed to reach significance for children with ADHD (Kray et al., 2012). As argued below, the finding that set shifting training produces improvements in mixing costs but not set shifting (shift costs) is generally consistent with the hypothesis that children with ADHD’s difficulties on set shifting tasks may be artifacts of difficulties in other higher-order cognitive functions rather than reflective of true deficits in set shifting (e.g., Irwin et al., 2019).

² An additional 19 children were evaluated by our research clinic during this time-period (i.e., March 2017-March 2019), but were not eligible as they did not meet criteria for a diagnosis of ADHD.

Additional information

Funding

This work was supported in part by NIH grant R01 MH115048 (PI: Kofler). The sponsor had no role in design and conduct of the study; collection, management, analysis, and interpretation of the data; or preparation, review, or approval of the manuscript.