Independent contributions of cortical gray matter, aging, sex and alcoholism to K-complex amplitude evoked during sleep

Abstract

Study objectives: The amplitude of the N550 component derived from the averaged evoked K-complex decreases with normal aging and with alcoholism. The study was designed to determine whether these declines are related to the extent of cortical or subcortical shrinkage.

Setting: Research sleep laboratory and MR imaging facility

Participants: 26 abstinent long-term alcoholic men, 14 abstinent long-term alcoholic women, 18 control men, and 22 control women.

Measurements and results: MRI data collected at 3T were analyzed from alcoholic and control men and women previously reported to have significantly different evoked delta activity during sleep. Segmented and parcellated MRI data collected at 3T were compared between these groups and evaluated for correlation with evoked K-complex amplitude measured at FP1, Fz, FCz, Cz, CPz, and Pz. Cortical gray matter and regional subcortical tissue volumes entered as predictors into stepwise multiple regression identified cortical gray matter as a unique significant predictor of evoked K-complex at all sites. Age added independent variance at 5 of the 6 sites, while alcoholism and sex added independent variance at frontal sites only.

Conclusions: These data support recent intracranial studies showing cortical generation of K-complexes by indicating that cortical, but not subcortical volume contributes to K-complex amplitude. Establishing the extent of the relation between cortical volume and K-complex amplitude provides a mechanistic understanding of sleep compromise clinically relevant to normal aging, alcoholism, and likely other conditions affecting cortical volume and integrity.

Keywords: Delta; ERP; MRI.

Figure 1

(A) Surface-rendered brain from the SRI24 atlas (http://nitrc.org/projects/sri24), showing the cortical regions for gray matter volume evaluation. The frontal lobe is shown in red, the sensorimotor cortex in green, the parietal lobe in yellow, the occipital lobe in light blue, and the temporal lobe (minus the temporal pole) in dark blue. The bottom right of the panel shows a 2-dimensional representation of a coronal slice showing an outline of the parcellated cortical surface. (B) Cortical gray matter volumes expressed as a proportion of ICV for control and alcoholic men and women. Error bars reflect standard deviations around each mean value. (C) Subcortical tissue volumes expressed as a proportion of ICV for control and alcoholic men and women. Error bars reflect standard deviations around each mean value. *indicates a significant effect of alcoholism diagnosis (P < 0.01).# indicates a significant effect of sex (P < 0.01).

Figure 2

The relationship between N550 amplitude measured at FP1, Fz, FCz, Cz, CPz, and Pz and the standardized predicted values from Model 6 (frontal, sensorimotor, temporal, parietal, and occipital gray matter volumes; anterior, middle, and posterior cingulate tissue volumes; thalamus, hippocampus, and basal ganglia tissue volumes; age, sex; and alcoholism diagnosis). Men are represented by triangles and women by circles. Alcoholics are represented as filled symbols and controls as open symbols. In each panel, the line shows the linear regression relationship between the standardized model predictor and N550 for all subjects combined. Note that N550 is a negative component and thus more negative amplitudes on the X axis and more negative Z scores on the Y axis each indicate larger responses.