Karalunas, S. L., Gustafsson, H. C., Dieckmann, N. F., Tipsord, J., Mitchell, S. H., & Nigg, J. T. (2017). Heterogeneity in development of aspects of working memory predicts longitudinal attention deficit hyperactivity disorder symptom change. Journal of abnormal psychology, 126(6), 774.
Goal: Investigate trajectories of cognitive ability in TD and ADHD children and the relationship to ADHD symptom burden
Methods: 734 children (437 diagnosed with ADHD) ages 7-13 years played tasks measuring response inhibition, visual-spatial working memory, and delayed reward discounting. These tasks were collected at three annual visits. Parent (KSAD) and teacher (ADHD-RS) reports of ADHD symptom burden (separately for inattention and hyperactivity) were collected. They ran conditional latent growth curve models (LCMs) to establish the growth trajectory of each cognitive skill in the full sample and to test for overall differences in the TD and ADHD groups. They ran latent class growth analyses (LCGAs) to test for subgroups within ADHD and TD groups based on unique growth trajectories (does not assume that a group is homogenous).
LCM Results:
- Response inhibition: Both TD and ADHD children displayed a linear increase in response inhibition, with ADHD children displaying poorer performance throughout.
- Visual-spatial working memory: Both TD and ADHD children displayed a linear increase in response inhibition, but ADHD children displayed a less steep slope increase over time (suggesting ADHD children fall behind their TD peers).
- Delayed reward discounting: At age 7, children with ADHD displayed greater discounting of delayed rewards than their TD peers. Between ages 7-10, children with ADHD had a steeper rate of improvement than TD children so that the groups did not differ at age 11. From ages 11-13 there were no group differences in delayed reward discounting.
LCGA Results:
- Response inhibition: The TD children were split into two classes (a) “control: normally developing” and (b) “control: impaired” which had impaired response inhibition at 7, improved more rapidly over time, but did not reach the level of group (a) by 13 years. The children with ADHD were split into two classes (c) “adhd: unimpaired” and (d) “adhd: impaired” which had impaired response inhibition at 7 compared to (a), improved more rapidly over time than (c), but did not reach the level of all other groups (a, b, c) by 13 years.
- Visual-spatial working memory: The TD children were split into two classes (e) “control: normally developing” and (f) “control: impaired” which had impaired VWM at age 7 and slower improvement. The children with ADHD were split into three classes (g) “adhd: impaired, recovering” with steeper improvement slopes and normalized VWM at 13 years, (h) “adhd: stably impaired” that did not significantly improve over time, and (i) “adhd: high VWM” with no impairment at 7 years even exceeding (e) but did not improve over time and did not exceed (e) at 13 years.
- Delayed reward discounting: The TD children were best fit with a one-class solution, which suggests no distinct trajectory classes. The children with ADHD were split into two classes (j) “adhd: impaired” worse DRD at 7 years but more rapid improvement through 11 and then no improvement through 13 years and (k) “adhd: unimpaired” with DRD similar to controls at 7 years and then improvement through 11 years and then some worsening of DRD through 13 years.
ADHD Symptom Burden x Trajectories Results:
- Response inhibition: No differences in ADHD symptoms at baseline or across symptom trajectory, except teacher report indicated that the “adhd: unimpaired” group had a more rapid decreases in inattention symptoms than “adhd: impaired.”
- Visual-spatial working memory: No differences in hyperactivity/impulsivity symptoms. With regard to inattention, the “adhd: stably impaired” group had higher baseline inattention symptoms than the other groups and had less improvement over time while the “adhd: high VWM” and “adhd: impaired, recovering” groups did not differ from each other.
- Delayed reward discounting: No differences in symptom burden between ADHD groups.
Discussion: Trajectories of visual-spatial working memory related to inattention symptom burden more than trajectories of response inhibition and delayed reward discounting. This research aligns with prior work showing that neurocognitive impairments relate more strongly to inattention as opposed to hyperactivity/impulsivity symptoms. The authors underscore the importance of longitudinal testing and of sorting into sub-diagnostic groups based on trajectories, as simply grouping based on baseline assessments would not have distinguished between VWM groups
Thoughts:
- The authors suggest that future studies should (1) use multiple indicators of latent variables and (2) look at neurocognitive trajectories across puberty. EF Study data can address both of these.
- The TD and ADHD groups are subtyped separately in this study. Additionally ADHD symptom burden measures were not collected from the TD group. I would be interested in combining the groups and relating to continuous measures of symptom burden.