Gray Matter Volume Correlates of Sleepiness: A Voxel-Based Morphometry Study in Younger and Older Adults

Figures & data

Table 1 Background Data for the Two Age Groups, and ANOVA Results for the Difference Between Groups

	Young Mean±SD	Older Mean±SD	F	P
N	42	42
Age	23.8±2.6	68.6±2.6
BMI	22.9±3.14	24.5±3.36	4.7	0.033
Subjective health (1–7)	4.58±0.54	4.67±0.54	0.5	0.463
Women %	52%	47%	0.2	0.850
HADS anxiety	3.02±2.5	1.33±1.4	13.3	0.001
HADS depression	1.20±1.37	1.14±0.99	0.1	0.750
ISI	10.6±2.1	9.1±1.6	13.9	0.001
KSQ (1–6)	5.26±0.42	5.23±0.50	0.1	0.798
Enough sleep (1–6)	4.11±0.74	4.56±0.50	9.4	0.003
Sleep need (h)	7.86±0.88	7.39±0.85	5.8	0.018
Habitual sleep duration (h)	8.53±1.30	8.22±1.30	1.1	0.290
Recorded sleep (TST, h)	6.61±1.30	7.16±1.40	6.05	0.017

Abbreviations: N, number of participants; KSQ, Karolinska Sleep Questionnaire; ISI, Insomnia Severity Scale (see below for details); HADS, Hospital Anxiety and Depression Scale; BMI, body mass index; TST, total sleep time (from polysomnography); h, hours; F, F-ratio; p, p-value for statistical significance.

Figure 1 Demonstration of anatomically defined regions of interest (ROIs): insula cortex, hippocampus, frontal superior orbitofrontal cortex/rectus gyrus and thalamus.

Table 2 Age Group Interactions of Associations Between Sleepiness (KSS Scores) and GM Volume

Region of Interest (ROI)	Age Effect	MNI (x, y, z)	Z	Voxels (mm^3)	P^FWE
L insula	Interaction Y+ O–	–34, 8, –15	4.02	6605	0.015
R insula	Interaction Y+ O–	32, 9, –18	4.42	5947	0.009
L Sup OFC/rectus gyrus	Interaction Y+ O–	–10, 20, –14	2.16	∞	0.895
R Sup OFC/rectus gyrus	Interaction Y+ O–	8, 21, –20	2.18	2271	0.884
L hippocampus	Interaction Y+ O–	–24, –22, –16	3.12	2457	0.149
R hippocampus	Interaction Y+ O–	15, –32, 9	3.17	2977	0.131
L thalamus	Interaction Y+ O–	–15, –22, 2	3.75	3068	0.020
R thalamus	Interaction Y+ O–	20, –26, 4	4.60	4074	0.001

Notes: Y+ indicates a positive association in younger adults, and O– indicatesnegative association in older adults. ^∞Effects seen in left and right hemisphere belongs to the same cluster of GM volume; bold= significant p-values. x, y, z = coordinates.

Abbreviations: GM, gray matter; MNI, Montreal Neurological Institute; L, left; R, right; Sup OFC, frontal superior orbitofrontal cortex; FWE, family wise-error correction; KSS, Karolinska Sleepiness Scale.

Figure 2 Demonstration of sleepiness (KSS scores)-associated thalamic gray matter volume in younger and older adults. The plots show the age interaction effect suggesting that sleepiness is negatively associated with left and right thalamus gray matter volume in older adults, but positively associated in younger individuals. The colors in the brain plot represent statistical t-values ranging from 0 (black) to 5.0 (white).

Abbreviation: KSS, Karolinska Sleepiness Scale.

Figure 3 Demonstration of sleepiness (KSS scores)-associated insula gray matter volume in younger and older adults. The plots show the age interaction effect suggesting that sleepiness is positively associated with left and right insula gray matter volume in younger adults, but negatively associated in older individuals. The colors in the brain plot represent statistical t-values ranging from 0 (black) to 4.5 (white).

Abbreviation: KSS, Karolinska Sleepiness Scale.

Table 3 Exploratory Whole-Brain Analyses on Age Group Interactions of Associations Between Sleepiness (KSS Scores) and GM Volume

Region	Age Effect	MNI (x, y, z)	Z	Voxels (mm^3)	P(Uncorr)
R thalamus	Interaction Y+ O–	20, –26, 4	4.60	1485	<.001
R insula	Interaction Y+ O–	32, 8, –18	4.35	1593	<.001
L insula	Interaction Y+ O–	–34, 8, –16	4.28	2228	<.001
R insula	Interaction Y+ O–	44, 16, –6	4.09	378	<.001
L cerebellum	Interaction Y+ O–	–18, –74, –48	4.01	1529	<.001
R cerebellum	Interaction Y+ O–	46, –74 –32	3.83	1232	<.001
L thalamus	Interaction Y+ O–	–15, –22, 2	3.75	270	<.001
R postcentral	Interaction Y+ O–	39, –34, 58	3.60	250	<.001
R cerebellum	Interaction Y+ O–	8, –48, –36	3.36	95	<.001
L parietal superior	Interaction Y+ O–	–27, –62, 44	3.36	139	<.001
R cerebellum	Interaction Y+ O–	26, –78, –54	3.32	422	<.001

Notes: Y+ indicates positive association in younger adults, and O– indicatesnegative association in older adults.

Abbreviations: GM, gray matter; MNI, Montreal Neurological Institute; L, left; R, right; KSS, Karolinska Sleepiness Scale; Uncorr, uncorrected. x, y, z = coordinates.

Table 4 Exploratory Whole-Brain Main Effects of Associations Between Sleepiness (KSS Scores) and GM Volume for Both Groups Together.

Region	Age Effect	MNI (x, y, z)	Z	Voxels (mm^3)	P (Uncorr)
R frontal mid orbitofrontal	Main YO+	22, 52, –10	3.52	135	<.001
L cerebellum	Main YO–	–12, –58, –62	4.21	1225	<.001
R cerebellum	Main YO–	28, –84, –39	3.83	425	<.001
L rolandic operculum	Main YO–	–45, –6, 4	3.72	246	<.001
R cerebellum	Main YO–	15, –57, –63	3.69	516	<.001

Notes: YO+ and YO– indicate the sign of the (+, positively; –, negatively) across both age groups. x, y, z = coordinates.

Abbreviations: GM, gray matter; MNI, Montreal Neurological Institute; L, left; R, right; KSS, Karolinska Sleepiness Scale; Uncorr, uncorrected.

All of the Ps are Presented at an uncorrected level.