The effect of sleep fragmentation on sleep and performance in younger and older subjects

Groups of 12 normal 55-70-year-old and young adult subjects had their sleep experimentally disturbed at a rate of approximately 14 times per hour to determine the residual effects of moderate sleep disturbance and to determine any differential impact as a function of age. Normal age-related changes in sleep were seen on baseline and recovery nights. In the second night of sleep disturbance, the older subjects had a smaller increase in total awakenings than young adults. Older subjects had a slower increase in auditory arousal threshold as sleep disturbance progressed. The older subjects also tended to have less performance deterioration on morning testing than did young adults, and this difference was significant for numbers of correctly completed addition problems. These evidences led to the conclusion that, while both age groups were sensitive to moderate sleep disturbance, the older individuals appeared somewhat less sensitive than the young adults.     

Relationship between sensorimotor adaptation and cognitive functions in younger and older subjects

We investigated whether deficits of adaptive improvement in seniors are related to an age-dependent decay of the brain’s executive functions. Younger and older subjects completed a battery of cognitive tests, and preformed aimed arm movements before and during exposure to rotated visual feedback. In accordance with previous work, we found that adaptive improvement during exposure was degraded in seniors, while the transfer of adaptation to a new motor task was not. This pattern of findings confirms that strategic control but not sensorimotor recalibration is affected by old age. Using multiple linear regression (MLR) to extract separate executive components from our test battery, we found that basic response speed and decision-making, but not the inhibition of prepotent responses or mental flexibility, were degraded in our older subjects. Again using MLR, we found that degraded adaptive improvement in our seniors was partly related to the decay of basic response speed and decision-making, and partly to age-dependent phenomena not addressed by our cognitive-test battery. Finally, we observed that interindividual variability of cognition and adaptive improvement was larger in old than in young subjects, which could explain why some previous studies found degraded adaptation in seniorswhile others did not.     

Autonomic and electrophysiological correlates of emotional intensity in older and younger adults

Anterior cingulate cortex (ACC) is involved in the modulation of autonomic activity, emotional responsivity, and the monitoring of goal-directed behavior. However, these functions are rarely studied together to determine how they relate or whether their pattern of relation changes with age. We recorded respiratory sinus arrhythmia (RSA), an index of autonomic activity, error-related event related potentials (ERN/Pe), generated in ACC, and the self-reported intensity of 5 basic emotions in older and younger adults. Emotional intensity did not differ with age. The ERN/Pe and RSA were reduced with age and related specifically to sadness intensity for both groups. When examined together, RSA accounted for the relation between ERN/Pe and sadness. This is consistent with a model of medial prefrontal function in which autonomic processes mediate the relation between cognitive control and affective regulation, a pattern that also did not differ with age.     

Spatial organization of EEG activity from alertness to sleep stage 2 in old and younger subjects

In order to elucidate brain mechanisms that contribute to the increased tendency for vigilance dysregulation in the elderly, we examined the spatial organization of brain electric activity [electroencephalogram (EEG)] during decreasing vigilance from alertness to onset of sleep stage 2, comparing 7 old and 10 younger, healthy subjects (60-79 and 18-41 years old, respectively). Two features were analyzed: (1) change of location of the brain electric source gravity centers of the EEG frequency bands, and (2) magnitude of fluctuation of these locations over time. Multichannel EEG was analyzed into source gravity center localizations for seven EEG frequency bands, using fast Fourier transform (FFT) Dipole Approximation (first principal component-single source modeling in the frequency domain). Multivariate analysis of covariance (MANCOVA) showed: source localizations were more anterior in old than younger subjects for beta-1 and more superior for all three beta bands; from alertness to sleep, delta and theta EEG sources (inhibitory activity) changed to more posterior and superior areas, and alpha-1 and -2 (routine activity) and beta-1 and -2 sources (excitatory activity) towards anterior and superior areas. Fluctuations of the source locations of delta and beta-2 were larger on the superior--inferior axis, and of beta-2 smaller on the left-right axis in the old than younger subjects. The results suggest functional specifications (inhibitory, routine, excitatory) of cortical positron emission tomography (PET) changes reported in sleep. In sum, aging exhibits changes in spatial organization of EEG-generating neuronal assemblies; during the transition wakefulness-to-sleep, aging affects the spatial-temporal dynamics of this organization. The latter is suggested to contribute to the increased risk for consciousness disturbances in the elderly.     

Circadian patterns of sleep, sleepiness, and performance in older and younger adults

STUDY OBJECTIVE: To compare circadian patterns of sleep, subjective sleepiness, and psychomotor performance in older and younger adults. DESIGN: Controlled experimental laboratory study. SETTING: General Clinical Research Center. PARTICIPANTS: Healthy older adults (n = 17, mean age 76 years) and healthy younger adults (n = 19, mean age 23 years). INTERVENTIONS: Subjects lived for 60 consecutive hours on a 90-minute sleep-wake cycle (30 minutes in bed, 60 minutes awake). Electroencephalographic recordings were conducted during bedrest periods. Self-ratings and psychomotor performance tests were conducted during 60-minute wake periods. MEASUREMENTS AND RESULTS: Data were analyzed with cosinor and linear mixed models. Amplitude and phase of the core body temperature rhythm did not significantly differ by age group. Older adults had significantly reduced mean levels and amplitude of rhythms in total sleep time and sleep efficiency and increased mean levels and amplitude of rhythms in sleep latency and wake after sleep onset. Age groups did not differ in mean level of subjective sleepiness, but older adults had reduced amplitude. Older adults had worse overall psychomotor performance, with evidence of larger circadian amplitude in some of these rhythms. Age groups did not differ on the phase position of any rhythm. CONCLUSIONS: Older adults had a lower level and smaller circadian variation of sleep propensity compared with younger adults, whereas wakefulness and psychomotor performance rhythms tended to show increased circadian variation among older subjects. These findings likely result from a combination of age-related changes in cortical function, homeostatic sleep mechanisms, and circadian regulation.     

Comparison of subjective and objective assessments of sleep in healthy older subjects without sleep complaints

Older adults have reduced sleep quality compared with younger adults when sleeping at habitual times and greater sleep disruption when their sleep is at adverse times. The purpose of this analysis was to investigate how subjective measures of sleep relate to objectively recorded sleep in older subjects scheduled to sleep at all times of day. We analyzed data from 24 healthy older (55–74 years) subjects who took part in a 32-day inpatient study where polysomnography was recorded each night and subjective sleep was assessed after each scheduled wake time. The study included baseline nights and a forced desynchrony (FD) protocol when the subjects lived on a 20-h rest activity schedule. Our postsleep questionnaire both included quantitative and qualitative questions about the prior sleep. Under baseline and FD conditions, objective and subjective sleep latency were correlated, subjective sleep duration was related to slow-wave sleep and wake after sleep onset, subjective sleep quality was related to stage 1 and 2 sleep, and sleepiness and refreshment at wake time were related to duration of premature awakening. During FD, most measures of objective and subjective sleep varied with circadian phase and many additional correlations between objective and subjective sleep were present. Our findings show that when sleeping at habitual times, these healthy older subjects did not perceive their generally poor sleep quality, but under FD conditions where sleep quality changed from day-to-day their subjective sleep ratings were more associated with their objective sleep.     

Electroencephalographic sleep and natural killer activity in depressed patients and control subjects.

Insomnia is associated with a reduction of natural killer (NK) activity in depression independent of the severity of other depressive symptoms. This study extends these findings by exploring the relationship between objective electroencephalographic (EEG) assessment of sleep and values of NK activity in depressed patients (n = 23) and in control subjects (n = 17). The sleep EEG parameters total sleep time, sleep efficiency, and duration of nonREM sleep were each positively correlated with NK activity in the depressed patients and in the control subjects, demonstrating similar relationships between the amount of sleep and NK activity in the separate groups. These observations support the hypothesis that sleep measures are associated with NK cytotoxicity, independent of the effects of severity of depressive symptoms or the presence of a mood disorder.     

Behavioural and electrophysiological effects of visual paired associate context manipulations during encoding and recognition in younger adults,older adults and older cognitively declined adults

The current study examined the EEG of young, old and old declined adults performing a visual paired associate task. In order to examine the effects of encoding context and stimulus repetition, target pairs were presented on either detailed or white backgrounds and were repeatedly presented during both early and late phases of encoding. Results indicated an increase in P300 amplitude in the right parietal cortex from early to late stages of encoding in older declined adults, whereas both younger adults and older controls showed a reduction in P300 amplitude in this same area from early to late phase encoding. In the right hemisphere, stimuli encoded with a white background had larger P300 amplitudes than stimuli presented with a detailed background; however, in the left hemisphere, in the later stages of encoding, stimuli presented with a detailed background had larger amplitudes than stimuli presented with a white background. Behaviourally, there was better memory for congruent stimuli reinstated with a detailed background, but this finding was for older controls only. During recognition, there was a general trend for congruent stimuli to elicit a larger amplitude response than incongruent stimuli, suggesting a distinct effect of context reinstatement on underlying patterns of physiological responding. However, behavioural data suggest that older declined adults showed no memory benefits associated with context reinstatement. When compared with older declined adults, younger adults had larger P100 amplitude responses to stimuli presented during recognition, and overall, younger adults had faster recognition reaction times than older control and older declined adults. Further analysis of repetition effects and context-based hemispheric asymmetry may prove informative in identifying declining memory performance in the elderly, potentially before it becomes manifested behaviourally.     

Association between polysomnographic sleep measures and health-related quality of life in obstructive sleep apnea

Many facets of health-related quality of life are diminished in obstructive sleep apnea (OSA) as they are in other chronic medical conditions. We speculated that impairment in health-related quality of life (HRQoL) might result from the fatigue and daytime somnolence associated with the sleep disorder, as an indirect result from the fragmentation of night-time sleep in OSA. Our hypothesis was that sleep fragmentation measures would correlate with poorer HRQoL measured by medical outcomes study (MOS) subscales. Thirty-nine patients with polysomnographically-confirmed OSA participated in this study. Pearson's correlations were performed with the following sleep architecture variables: wake after sleep onset, the total number of brief arousals, the number of respiratory-related arousals, the rate of respiratory events per hour, and total sleep time. To our surprise, although the total number of arousals was associated with health distress (r=-0.481, P < 0.005), it did not correlate with any other subscales indicating poorer physical and mental health. The relatively insensitive measure of total sleep time (TST) correlated in the expected direction with most subscales. However, after controlling for age and gender, respiratory disturbance indices (RDI) and/or number of arousals emerged as significantly associated with mobility, cognitive functioning, social functioning, energy and fatigue, and health distress. Our findings suggest that polysomnographic indicators of sleep quality and sleep continuity may be an important influence determining many aspects of HRQoL in OSA patients.     

Pupillometry as a measure of cognitive effort in younger and older adults

Two experiments examined the effectiveness of the pupillary response as a measure of cognitive load in younger and older adults. Experiment 1 measured the change in pupil size of younger and older adults while they listened to spoken digit lists that varied in length and retained them briefly for recall. In Experiment 2 changes in relative pupil size were measured while younger and older adults listened to sentences for later recall that varied in syntactic complexity and sentence length. Both age groups' pupil sizes were sensitive to the size of the memory set in Experiment 1 and sentence length in Experiment 2, with the older adults showing a larger effect of the memory load on a normalized measure of pupil size relative to the younger adults. By contrast, only the younger adults showed a difference in the pupillary response to a change in syntactic complexity, even with an adjustment for the reduced reactivity of the older pupil.     

EEG spectral power analysis of phasic and tonic REM sleep in young and older male subjects

EEG spectral power was studied during periods of rapid eye movements (REMs) and tonic intervals in REM sleep of 7 young and 7 older male subjects. Significant symmetrical decreases in alpha and beta1 power at central and occipital sites, concurrent with an increase in frontal theta power, were observed during the production of REMs. The former findings are discussed as sleep analogues to changes in alpha and beta1 during waking, showing increased information processing and behavioural activation, and that of theta is tentatively presented as reflecting an increase in afferent thresholds. Independent of the phasic-tonic REM distinction, total EEG power markedly decreased as a function of time of night and did not interact with age. Significant age differences in the overall spectral composition of the EEG were obtained, namely, a lower level of delta power and a relative shift towards more power in frequencies above 12 Hz for the older group. Further, older subjects also demonstrated a more uniform topographical distribution of alpha and sigma power.     

Automatic quantification of light sleep shows differences between apnea patients and healthy subjects.

A fully automatic method to quantify sleep depth during the night was developed in the present work. The method was tested using 20 all-night recordings from 10 healthy control subjects and 10 sleep apnea patients. The results showed statistically significant differences in sleep depth between control subjects and sleep apnea patients. The overall sleep was lighter in apnea patients than in healthy control subjects, most likely indicating a disturbed sleep caused by apneas. The automatic parameters presented provide a method to quantify the light sleep and could in the future possibly be used in clinical sleep studies and follow-up of treatment.     

Bipolar radiofrequency in the human meniscus. Comparative study between patients younger and older than 40 years of age

PURPOSE: To morphohistologically evaluate the effect of four increasing intensities of bipolar radiofrequency (RF) on the human meniscus and to compare the changes seen in the menisci from patients younger and older than 40 years old. METHODS: Thirty fresh menisci were divided in two groups. Group 1: 12 menisci from patients younger than 40 y.o.; Group 2: 18 menisci from patients older than 40 y.o. Groups 1 and 2 were divided in four zones and subjected in vitro, for 3 s, to four intensities of bipolar RF energy. The samples were studied macroscopically, and microscopically. RESULTS: Thermal changes were present between 0 and 4000 microm from the meniscal surface, with an average of 1699 microm (S.D. 740), and was significantly higher on the ablation than the coagulation group (p<0.001). We found a significant difference between the depth of thermal changes in the menisci from patients younger and older than 40 years old at medium intensities of RF energy (p=0.038 and p=0.044). CONCLUSIONS: Although bipolar RF can cause deep thermal changes (up to 4000 microm) on the human meniscus, this effect depends on the magnitude of the energy applied. When comparing the effect between younger and older patients, the changes were deeper in the older group when RF was applied at medium intensities. CLINICAL RELEVANCE: Based on our findings, we recommend to exert precaution when applying RF energy at medium intensities in the degenerative meniscus, due to a deeper thermal effect in this group.     

The relationship between a night's sleep and subsequent daytime functioning in older poor and good sleepers

Those suffering insomnia symptoms generally report daytime impairments. However, research has not assessed whether this relationship holds on a nightly basis, despite the strongly held belief that a night of poor sleep impairs mood and functioning the following day. The objective of this study was to test this relationship in a group of older poor sleepers with insomnia symptoms compared with good sleepers. This study utilized a within‐subjects design to investigate day‐to‐day subjective daytime functioning and its relation to the previous night's sleep. Seventeen older individuals (mean age: 67.5 years) were identified with a retrospective questionnaire and 2 weeks of sleep–wake diary to have poor sleep consistent with insomnia. Seventeen good sleepers (mean age: 67.8 years) were selected using the same measures. Participants reported their beliefs about sleep and daytime functioning on the Dysfunctional Beliefs and Attitudes about Sleep Scale (DBAS‐16). One week later they commenced a 14‐day period of sleep–wake diaries and concurrent responses to a modified Daytime Insomnia Symptom Scale (DISS). Results showed significant night‐to‐day covariation between sleep efficiency and daytime functioning for individuals with poor sleep (r = 0.34), but not for good sleepers (r = 0.08). Those poor sleepers who held this covariation belief most strongly were those who subsequently showed this night‐to‐day relationship the most strongly (r = 0.56). This was not true for good sleepers. For those suffering insomnia, these findings demonstrate their belief that a poor sleep is followed by an impaired daytime, consistent with their experience.     

The maturation of correlations between cardiac and respiratory measures across sleep states in normal infants.

Coordination of cardiac and respiratory measures is not mature in newborn infants but develops during early life. The course of that development is assessed in this study. Twelve-hour recordings of electrocardiogram, electroencephalogram, digastric electromyogram, electrooculogram and expired CO2 were obtained from 25 normal infants at 1 week and 1, 2, 3, 4 and 6 months of age. Each 1-minute epoch was classified as quiet sleep, rapid eye movement (REM) sleep, waking or indeterminate state. In each sleep-waking state, the correlations of heart rate with respiratory rate, heart rate with respiratory rate variability and respiratory rate with its own variability were determined on a minute-by-minute basis for each recording. The relative extents of correlations between measures and the maturational trends of these correlations were profoundly influenced by sleep-waking state. During quiet sleep, two of the three correlations weakened significantly over the first month of life, but, in the waking state, the same correlations strengthened over this period. During quiet sleep and waking, the three correlations showed similar patterns of development, but the three showed dissimilar developmental trends during REM sleep. These dissimilarities may reflect changes in the nature of REM sleep consequent to myelination of rostral brain pathways.