Sleep evoked delta frequency responses show a linear decline in amplitude across the adult lifespan

Abstract

Aging is associated with many changes in sleep, with one of the most prominent being a reduction in slow wave sleep. Traditional measures of this phenomenon rely on spontaneous activity and typically confound the incidence and amplitude of delta waves. The measurement of evoked K-complexes during sleep, enable separate assessment of incidence and amplitude taken from the averaged K-complex waveform. The present study describes data from 70 normal healthy men and women aged between 19 and 78 years. K-Complexes were evoked using short auditory tones and recorded from a midline array of scalp sites. Significant reductions with age were seen in the amplitude of the N550 component of the averaged waveform, which represents the amplitude of the K-complex, with linear regression analysis indicating approximately 50% of the variance was due to age. Smaller, yet still significant reductions were seen in the ability to elicit K-complexes. The data highlight the utility of evoked K-complexes as a sensitive marker of brain aging in men and women.

Figure 1

Age distribution of the sample. Histograms reflect the number of men (black) and women (gray) in each decade, with the count displayed on the left Y axis. The unfilled triangles reflect the mean age per decade of men and unfilled squares the mean age per decade of women, with the age values plotted on the right hand Y axis.

Figure 2

KC incidence (proportion of stimuli producing a K-complex) as a function of age. Data represent one point per subject, with the solid line indicating the linear regression function fitted to the data.

Figure 3

Grand mean waveforms for each decade. In each set of waveforms data are plotted with negative voltages up the Y axis.

Figure 4

N550 amplitude as a function of age at each electrode site. Data represent one point per subject, with the solid line indicating the linear regression function fitted to the data.

Figure 5

P2 amplitude as a function of age at each electrode site. Data represent one point per subject, with the solid line indicating the linear regression function fitted to the data.

Figure 6

P2 latency as a function of age at each electrode site. Data represent one point per subject, with the solid line indicating the linear regression function fitted to the data.