Sleep-Related Declarative Memory Consolidation in Children and Adolescents with Developmental Dyslexia

Abstract

Sleep has a crucial role in memory processes, and maturational changes in sleep electrophysiology are involved in cognitive development. Albeit both sleep and memory alterations have been observed in Developmental Dyslexia (DD), their relation in this population has been scarcely investigated, particularly concerning topographical aspects. The study aimed to compare sleep topography and associated sleep-related declarative memory consolidation in participants with DD and normal readers (NR). Eleven participants with DD and 18 NR (9-14 years old) underwent a whole-night polysomnography. They were administered a word pair task before and after sleep to assess for declarative memory consolidation. Memory performance and sleep features (macro and microstructural) were compared between the groups, and the intercorrelations between consolidation rate and sleep measures were assessed. DD showed a deeper worsening in memory after sleep compared to NR and reduced slow spindles in occipito-parietal and left fronto-central areas. Our results suggest specific alterations in local sleep EEG (i.e., sleep spindles) and in sleep-dependent memory consolidation processes in DD. We highlight the importance of a topographical approach, which might shed light on potential alteration in regional cortical oscillation dynamics in DD. The latter might represent a target for therapeutic interventions aimed at enhancing cognitive functioning in DD.

Keywords: EEG topography; Non-Rapid Eye Movement (NREM) sleep; Slow Wave Activity; developmental dyslexia; learning disabilities; memory consolidation; neurodevelopmental disorders; predictive neurocognitive factors; sleep oscillations; sleep spindles.

Figure 1

(A) Topographical distribution of relative EEG power of delta (0.5–4.75 Hz) activity during NREM sleep for the group with DD and the NR. The average values are color-coded, plotted at the corresponding position on the planar projection of the scalp surface and interpolated between electrodes. The maps are based on 28 EEG derivations of the international 10-10 system with linked mastoid reference, and then normalized to average power across the individual EEG maps. (B) Results of the statistical comparisons (two-tailed t-tests for independent samples) on EEG delta power of NREM sleep between the group of DD (n = 10) and the NR (n = 15). The statistical map reports the t-values for each scalp location.

Figure 2

(A) Whole frequency range (11–15 Hz), fast (13–15 Hz) and slow (11–13 Hz) spindle density topographical scalp maps in the group of DD and NR. The maps are based on the 28 derivation of the 10-10 system (electrodes positions indicated by black dots). Values are color-coded and plotted at the corresponding position on the planar projection of the hemispheric scalp model. Values between electrodes were interpolated. Values are expressed in terms of number of spindles divided by artifact-free NREM sleep minutes. (B) Results of the statistical comparisons (two-tailed t-tests for independent samples) on EEG delta power of NREM sleep between the group with DD (n = 10) and the NR (n = 15). The statistical map reports the t-values for each scalp location. White dots indicate significant differences after FDR correction (p < 0.0077).

Figure 3

Maps of the correlation coefficients (Spearman’s Rho) between the EEG power of SWA for each electrode (28 channels) and the sleep-dependent consolidation rate at Word pair task (WPT) for the group with DD (n = 10) and the NR (n = 15). The values of the correlation coefficients are color-coded, plotted at the corresponding position on the planar projection of the scalp surface, and interpolated between electrodes.

Figure 4

Maps of the correlation coefficients (Spearman’s Rho) between spindle density (all, fast and slow) for each electrode (28 channels) and the sleep-dependent consolidation rate at Word pair task (WPT) for the group with DD (n = 10) and the NR (n = 15). The values of the correlation coefficients are color-coded, plotted at the corresponding position on the planar projection of the scalp surface, and interpolated between electrodes.