Nighttime Sleep Characteristics and White Matter Integrity in Young Adults

Figures & data

Figure 1 Illustration of a representative actigraphic nighttime period. Standard parameters of the sleep wake-cycle (eg, wake-up and sleep onset times, duration of sleep and wake episodes) were assessed for the overall nighttime period. Wake episode frequency, duration, distribution, and localization were computed by halves of the nighttime period.

Table 1 Background Characteristics of Study Participants

	Reference Sleep (n = 27)	Short Sleep (n = 23)	Long Sleep (n = 23)	p-value
Female n (%)^a	11 (41%)	9 (39%)	15 (65%)	0.134
Birth weight (kg)	3.5 ± 0.1	3.5 ± 0.1	3.5 ± 0.1	0.976
Birth height (cm)	50.7 ± 0.3	50.6 ± 0.3	50.5 ± 0.3	0.948
Gestational age (weeks)	39.4 ± 0.2	39.3 ± 0.2	39.4 ± 0.2	0.938
IDA in infancy n (%)^a	14 (52%)	13 (57%)	10 (43%)	0.575
Intelligence quotient^b,c	90.2 ± 2.5	91.8 ± 1.6	91.9 ± 2.0	0.801
Socioeconomic status^b,d	34.3 ± 1.3	33.8 ± 1.1	32.0 ± 1.4	0.443
Maternal education (years)	9.1 ± 0.6	9.6 ± 0.4	9.9 ± 0.5	0.601
Age at test (years)	22.4 ± 0.3	22.4 ± 0.2	22.7 ± 0.3	0.771
Formal education (years)	11.5 ± 0.2	11.8 ± 0.2	11.1 ± 0.3	0.151
High school graduation n (%)^a	22 (81%)	20 (87%)	16 (70%)	0.106
BMI at test (kg/m^2)	26.8 ± 1.0	27.0 ± 0.9	26.9 ± 0.9	0.981
Smoking n (%)^a	12 (44%)	11 (48%)	10 (43%)	0.952
Snoring self-reported n (%)^a	11 (65%)	9 (39%)	13 (56%)	0.417
Epworth Sleepiness Scale (score)	7.6 ± 0.6	8.9 ± 0.8	8.6 ± 0.9	0.478
Pittsburgh Sleep Quality Index	5.4 ± 0.6	6.4 ± 0.7	4.9 ± 0.4	0.200

Notes: Values are expressed as mean ± standard error. One-way analysis of variance. ^aChi square test or adjusted chi-square test. ^bAt age 10 years. ^cWechsler Intelligence Scale for Children Revised. ^dModified Graffar index.

Abbreviation: IDA, iron-deficiency anemia.

Table 2 Sleep-Wake Cycle Parameters By Groups

	Reference Sleep Group (n = 27)	Short Sleep Group (n = 23)	Long Sleep Group (n = 23)	p-value
				Short vs Reference	Long vs Reference	Short vs Long
Overall nocturnal period
Wake-up time (h:min ± min)‡	8:55 ± 0.3	8:07 ± 0.3	9:41 ± 0.3	0.346	0.258	0.008
Nap episodes (number)	3.2 ± 0.3	3.1 ± 0.4	3.7 ± 0.4	0.997	0.724	0.714
Nap episodes mean duration (h)^†	0.3 ± 0.1	0.3 ± 0.1	0.3 ± 0.1	0.996	0.996	0.989
Sleep onset time (h:min ± min)‡	01:08 ± 0.3	01:28 ± 0.3	00:38 ± 0.3	0.790	0.654	0.253
Total sleep time (h)	7.4 ± 0.1	6.0 ± 0.1	8.8 ± 0.1	< 0.001	< 0.001	< 0.001
Wake after sleep onset (h)	0.3 ± 0.1	0.5 ± 0.1	0.6 ± 0.1	0.281	0.002	0.290
Wake episodes (number)	1.5 ± 0.2	2.1 ± 0.3	2.4 ± 0.3	0.198	0.088	0.837
Wake episodes mean duration (h)^†	0.2 ± 0.1	0.2 ± 0.2	0.2 ± 0.1	0.996	0.741	0.887
Latency to first wake episode (h)	3.9 ± 0.4	2.6 ± 0.4	3.7 ± 0.4	0.095	0.981	0.134
Longest wake episode duration (h)^†	0.3 ± 0.3	0.4 ± 0.3	0.3 ± 0.3	0.089	0.373	0.753
Sleep efficiency (%)	96.5 ± 0.8	92.9 ± 0.9	93.7 ± 0.9	0.008	0.041	0.822
First half of the nocturnal period
Wake after sleep onset (h)^†	0.1 ± 0.4	0.2 ± 0.4	0.2 ± 0.4	0.357	0.092	0.927
Wake percent after sleep onset	5.7 ± 1.2	9.9 ±1.3	6.8 ±1.2	0.109	0.923	0.389
Wake episodes (number)	0.8 ± 0.2	0.9 ± 0.2	1.0 ± 0.2	0.872	0.215	0.927
Longest wake episode localization (%)	37.7 ± 9.7	36.9 ± 9.8	24.6 ± 8.9	0.998	0.727	0.698
Second half of the nocturnal period
Wake after sleep onset (h)^†	0.2 ± 0.4	0.4 ± 0.5	0.4 ± 0.4	0.044	0.005	0.998
Wake percent after sleep onset	7.7 ± 1.0	13.9 ± 1.2	10.9 ± 1.1	< 0.001	0.036	0.283
Wake episodes (number)	1.3 ± 0.1	1.7 ± 0.2	1.9 ± 0.2	0.218	0.002	0.388
Longest wake episode localization (%)	62.3 ± 10.2	63.1 ± 9.6	75.4 ± 8.1	0.997	0.731	0.689

Notes: Values are expressed as mean ± standard error. Bonferroni adjusted p-values. General linear model.^† SE × 10^{1. ‡} Clock time.

Table 3 Cluster of White Matter Tracts With Lower Fractional Anisotropy Values in the Long Versus Reference Sleep Groups

Cluster	Cluster Extension	Cluster Size (Voxels)	MNI Coordinates of the Peak Voxel			Z Score
			x	y	z
1	Superior corona radiata L, body of corpus callosum, posterior corona radiata L, superior longitudinal fasciculus L, anterior thalamic radiation L	1398	−27	−5	27	0.034

Notes: Montreal Neurological Institute (MNI) template coordinates (x, y, z) and Z score refer to the voxel in the cluster with maximum probability.

Abbreviation: L, Left hemisphere.

Table 4 Clusters of White Matter Tracts With Higher Radial Diffusivity Values in the Long Versus Reference Sleep Groups

Cluster	Cluster Extension	Cluster Size (Voxels)	MNI Coordinates of the Peak Voxel			Z Score
			x	y	z
1	Body of corpus callosum	510	−14	−12	32	0.046
2	Body of corpus callosum, superior corona radiata L	306	10	−23	27	0.051

Notes: Montreal Neurological Institute (MNI) template coordinates (x, y, z) and Z score refer to the voxel in the cluster with maximum probability.

Abbreviation: L, Left hemisphere.

Figure 2 Fractional anisotropy differences between the Long and Reference sleep groups. The red-yellow color indicates the white matter clusters that showed lower fractional anisotropy values (α < 0.05, threshold-free cluster enhancement and family-wise error correction) in the Long sleep group compared with the Reference sleep group (at the indicated coordinates). The mean skeleton of fractional anisotropy is shown in green. The white matter tracts include the superior Corona radiata and the body of the corpus callosum. The coordinates are presented in Montreal Neurological Institute (MNI) template space.

Abbreviations: A, anterior; L, left.

Figure 3 Radial diffusivity differences between the Long and Reference sleep groups. The light-blue color indicates the white matter clusters that showed higher radial diffusivity values (α ≤ 0.05, threshold-free cluster enhancement and family-wise error correction) in the Long sleep group compared with the Reference sleep group (at the indicated coordinates). The mean skeleton of FA is shown in green. The white matter tract includes the body of corpus callosum. Coordinates are presented in Montreal Neurological Institute (MNI) template space.

Abbreviations: A, anterior; L, left.