Does sleep help children with ADHD lock in rewarded habits?
Healthy boys held on to reward-learned choices more strongly after a night's sleep than after a day awake, but boys with ADHD and conduct problems showed no such sleep benefit.
Source
Sleep-Dependent Consolidation of Rewarded Behavior Is Diminished in Children with Attention Deficit Hyperactivity Disorder and a Comorbid Disorder of Social Behavior
Study at a glance
- Design
- Human experiment — Mixed design: each boy learned a probabilistic reward task, then had a 12-hour retention interval containing either a night of sleep (polysomnography) or a day awake, followed by a reversal block; patients vs controls compared.
- N
- N=34 · 34 boys: 17 inpatients with ADHD plus comorbid conduct or oppositional defiant disorder and 17 healthy controls, each tested in both sleep and wake conditions.
- Population
- Boys aged 8-12 from Kiel, Germany: psychiatric inpatients with ADHD + CD/ODD and typically developing controls
- Outcome
- Drop in preference for the previously rewarded choice from the end of encoding to the start of reversal learning (resistance to reversal as a consolidation index); correlations with REM and non-REM sleep
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What they did
Boys with ADHD plus conduct or oppositional defiant disorder and matched healthy boys played a 'pirate game' in which they learned by trial and error which of two islands usually hid treasure. After 12 hours spent either asleep overnight in a sleep lab or awake during the day, they replayed one learned pair with the rewards secretly reversed, so persisting with the old choice indicated how well the earlier learning had been consolidated. Sleep was recorded with EEG, and alertness, mood and wakefulness were measured as controls.
What they found
Both groups learned the task equally well and slept similar amounts. The key three-way interaction showed that healthy boys' preference for the old choice was harder to reverse after sleep than after wake, whereas in the ADHD group sleep and wake did not differ. Contrary to the prediction that REM sleep drives reward consolidation, healthy boys' consolidation tended to track non-REM sleep more than REM sleep.
The limits
What it doesn't show
The sample was small and all-male, and patients were severe inpatients with comorbid conduct or oppositional disorders, so the result may not apply to girls or to milder, pure ADHD, as the authors note. The sleep-stage conclusions rest on a difference between two non-significant correlations, and the group effect disappeared when subjective wakefulness was added as a covariate. Sleep stages were not experimentally manipulated, so the study cannot show which part of sleep causes consolidation.
Key terms
- Memory consolidation
- The process by which newly learned information is stabilised in memory after learning, often thought to be helped by sleep.
- Reversal learning
- Relearning after the reward rules are swapped; the harder it is to switch, the more firmly the original learning was stored.
- Probabilistic feedback
- Rewards that follow the correct choice only most of the time, so the learner must integrate outcomes across many trials.
- Polysomnography
- Overnight recording of brain waves, eye movements and muscle tone used to score sleep stages such as REM and slow-wave sleep.
- Comorbidity
- Having two or more diagnosed disorders at once, here ADHD together with conduct or oppositional defiant disorder.
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Quiz yourself
In this study, what indicated stronger consolidation of the rewarded choice?
Common questions
Why is being worse at reversal a sign of better memory here?
If the old rewarded choice has been strongly consolidated, the child keeps choosing it when the rules flip, so performance drops more at the start of reversal.
Could the ADHD group simply be less motivated or more tired?
The groups learned equally well, and the result held when controlling for psychopathology, memory and alertness; only adding subjective wakefulness made it non-significant.
Did the study support the idea that REM sleep strengthens reward memories?
No. In healthy boys consolidation related more to non-REM than REM sleep, so the reward-activation model was not confirmed.
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