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Abstract
Despite a relatively large body of literature describing the characteristics of sleep
spindles and K-complexes in young adults, relatively little research has been conducted
in older individuals. The general consensus from the few studies that have addressed
this issue is that there is a progressive decrease in the number of spindles and K-complexes
with age, although there is large intra-individual variation. Whether or not these
changes are an inevitable consequence of the aging process can be addressed by studying
healthy older adults who provide an example of the effects of age independently from
those of disease.
Fourteen young adults (mean age=21.4+/-2.5 years) and 20 older adults (mean age=75.5+/-6.3
years) participated in the study. All subjects were neurologically and medically healthy
and were not taking any medications with a known effect on the central nervous system
or sleep. For each subject, a number of characteristics were determined including
the number, density (SS/min), amplitude and frequency of all spindles as well as the
number and density of K-complexes (KC/min).
Spindle number, density and duration as well as K-complex number and density were
all significantly lower in the elderly compared to the young adults. The EEG frequency
within the spindles was significantly higher in the elderly, although the absolute
difference was less than 0.5 Hz. Multiple regression analysis indicated that spindle
duration and K-complex density were able to predict over 90% of the variance in age.
The age-related decrease in sleep spindle and K-complex density is consistent with
previous reports and may be interpreted as an age-related alteration of thalamocortical
regulatory mechanisms.