(c).

Reference	Disorder	Cognitive impairment	Age	Sample size	Study design	Sleep measure		Cognitive measure (outcome/s)	Results
						Recording parameters	Spindles scoring		Sleep	Cognition	Sleep and cognition
Bruni et al., 2009 [106]	DD	None	DD: 8–16 Controls: 7–16	DD: 16 Controls: 11	Correlational study	PPSG 10–20 International system	Power spectra calculated for delta, theta, alpha, sigma, and beta Sleep spindles Scored during N2.	(1) Memory and learning transfer (2) Reading test (speed and accuracy) (3) Writing test (accuracy) (4) Intelligence WISC-IIIR	Compared to healthy controls DD participants had the following: (1) Less stage-shifts per hour (2) Lower N2% (3) Less N3% (4) Increase in power of frequency bands 0.5–3 Hz and 11-12 Hz during N2 and 0.5–1 Hz during N3 (5) Increased spindle density	Mean IQ DD: FSIQ: 93.9 VIQ: 90 PIQ: 98.9	Only in DD group: (1) Sigma power band in N2 was positively correlated with the memory and learning transfer reading test reading test (2) Spindle density was positively correlated with performance on the word reading test