***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Experimental data indicate a role for the prefrontal cortex in mediating normal sleep physiology , dreaming and sleep-deprivation phenomena . During nonr and om-eye-movement ( NREM ) sleep , frontal cortical activity is characterized by the highest voltage and the slowest brain waves compared to other cortical regions . The differences between the self-awareness experienced in waking and its diminution in dreaming can be explained by deactivation of the dorsolateral prefrontal cortex during REM sleep . Here , we propose that this deactivation results from a direct inhibition of the dorsolateral prefrontal cortical neurons by acetylcholine , the release of which is enhanced during REM sleep .  Sleep  deprivation influences frontal executive functions in particular , which further emphasizes the sensitivity of the prefrontal cortex to sleep STUDY OBJECTIVE To investigate the associations between sleep stage distributions and subsequent decline in cognitive function in older men over time . DESIGN A population -based prospect i ve sub study of the Osteoporotic Fractures in Men Study . SETTING S Six sites in the United States . PARTICIPANTS Community-dwelling men aged 67 y or older ( n = 2,601 ) , who were free of probable dementia at sleep visit . Follow-up averaged 3.4 y. MEASUREMENT AND RESULTS Sleep stages were identified by in-home polysomnography  at the initial sleep visit ( 2003 - 2005 ) . Cognitive outcomes were assessed with the  Trail Making Test Part B and Modified Mini-Mental State Examination ( 3MS ) at sleep visit and two follow-up visits . After adjusting for multiple confounders compared with men in the lowest quartile of percent of sleep time spent in Stage N1 , those in the highest quartile had a twofold increase in cognitive decline for both cognitive tests ( adjusted annualized percent change/y : Trail Making Test Part B Q1 = 1.06 , Q4 = 2.45 , P = 0.01 ; 3MS Q1 = -0.27 , Q4 = -0.48 , P = 0.03 ) . In addition , compared with men in the highest quartile , men in the lowest quartile of percent of sleep time in Stage R revealed more cognitive decline on the 3MS ( adjusted annualized percent change/y : Q1 = -0.49 , Q4 = -0.22 , P = 0.003 ) . These findings were consistent even after further adjustment of total sleep time and sleep disordered breathing . No significant relationships between other sleep stages ( N2 , N3 ) and cognitive change were found . CONCLUSION Increased time in Stage N1 and less time in Stage R are associated with worsening cognitive performance in older men over time OBJECTIVES 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 study ing healthy older adults who provide an example of the effects of age independently from those of disease . METHODS 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 ) . RESULTS 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 . CONCLUSIONS 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 The effect of sleep deprivation ( 40 h ) on topographic and temporal aspects of electroencephalographic ( EEG ) activity during sleep was investigated by all night spectral analysis in six young volunteers . The sleep-deprivation-induced increase of EEG power density in the delta and theta frequencies ( 1 - 7 Hz ) during nonREM sleep , assessed along the antero-posterior axis ( midline : Fz , Cz , Pz , Oz ) , was significantly larger in the more frontal derivations ( Fz , Cz ) than in the more parietal derivations ( Pz , Oz ) . This frequency-specific frontal predominance was already present in the first 30 min of recovery sleep , and dissipated in the course of the 8-h sleep episode . The data demonstrate that the enhancement of slow wave EEG activity during sleep following extended wakefulness is most pronounced in frontal cortical areas OBJECTIVE To investigate whether age-related and experimental reductions in SWS and sleep continuity are associated with increased daytime sleep propensity . METHODS Assessment of daytime sleep propensity under baseline conditions and following experimental disruption of SWS .  Healthy young ( 20 - 30 y , n = 44 ) , middle-aged ( 40 - 55 y , n = 35 ) and older ( 66 - 83 y , n = 31 ) men and women , completed a 2-way parallel group study . After an 8-h baseline sleep episode , subjects were r and omized to 2 nights with selective SWS disruption by acoustic stimuli , or without disruption , followed by 1 recovery night .  Objective and subjective sleep propensity were assessed using the  Multiple Sleep Latency Test ( MSLT ) and the Karolinska Sleepiness Scale ( KSS ) . FINDINGS During baseline sleep , SWS decreased ( P < 0.001 ) and the number of awakenings increased ( P < 0.001 ) across the 3 age groups . During the baseline day , MSLT values increased across the three age groups ( P < 0.0001 ) with mean values of 8.7 min ( SD : 4.5 ) , 11.7 ( 5.1 ) and 14.2 ( 4.1 ) in the young , middle-aged , and older adults , respectively . KSS values were 3.7 ( 1.0 ) , 3.2 ( 0.9 ) , and 3.4 ( 0.6 ) ( age-group : P = 0.031 ) . Two nights of SWS disruption led to a reduction in MSLT and increase in KSS in all 3 age groups ( SWS disruption vs. control : P < 0.05 in all cases ) . CONCLUSIONS Healthy aging is associated with a reduction in daytime sleep propensity , sleep continuity , and SWS . In contrast , experimental disruption of SWS leads to an increase in daytime sleep propensity . The age-related decline in SWS and reduction in daytime sleep propensity may reflect a lessening in homeostatic sleep requirement . Healthy older adults without sleep disorders can expect to be less sleepy during the daytime than young adults The relationship between habitual sleep and cognition in older adults with sleep complaints is poorly understood , because research has focused on younger adults , used experimental or retrospective quasi-experimental design s , and generally produced equivocal results . Prospect i ve studies using sleep diaries are rare , but may provide important insights into this relationship as they offer greater ecological validity and allow for examination of the impact of night-to-night variability in sleep ( an often overlooked aspect of sleep ) on cognitive performance . Seventy-two older adults ( Mage = 70.18 years , SDage = 7.09 years ) completed fourteen consecutive days of sleep diaries and paper/pencil self-administered cognitive tasks , including measures of processing speed ( Symbol Digit ) and reasoning ( Letter Series ) . Regression analyses revealed increased average total wake time ( TWT ) during the night was associated with higher Symbol Digit scores , β = 0.45 , P < 0.05 . Night-to-night variability in either total sleep time ( TST ) or TWT was not associated with either cognitive measure . Implication s and potential explanations for these initially counterintuitive findings are discussed STUDY OBJECTIVES Older adults and patients with dementia often have disrupted circadian activity rhythms ( CARs ) . Disrupted CARs are associated with health declines and could affect cognitive aging . We hypothesized that among older women , weaker CARs would be associated with poorer cognitive function 5 y later . DESIGN Prospect i ve observational study . SETTING Three US clinical sites . PARTICIPANTS There were 1,287 community-dwelling older women ( 82.8 ± 3.1 y ) participating in an ongoing prospect i ve study who were free of dementia at the baseline visit . MEASUREMENTS AND RESULTS Baseline actigraphy was used to determine CAR measures ( amplitude , mesor , and rhythm robustness , analyzed as quartiles ; acrophase analyzed by peak activity time < 13:34 and > 15:51 ) . Five years later , cognitive performance was assessed with the Modified Mini-Mental Status Examination ( 3MS ) , California Verbal Learning Task ( CVLT ) , digit span , Trail Making Test B ( Trails B ) , categorical fluency , and letter fluency  . We compared cognitive performance with  CARs using analyses of covariance adjusted for a number of health factors and comorbidities . Women in the lowest quartile for CAR amplitude performed worse on Trails B and categorical fluency compared to women in the highest quartile ( group difference ( d ) = 30.42 sec , d = -1.01 words respectively , P < 0.05 ) . Women in the lowest quartile for mesor performed worse on categorical fluency ( d = -0.86 words , P < 0.05 ) . Women with a later acrophase performed worse on categorical fluency ( d = -0.69 words , P < 0.05 ) . Controlling for baseline Mini-Mental State Examination and sleep factors had little effect on our results . CONCLUSION Weaker circadian activity rhythm patterns are associated with worse cognitive function , especially executive function , in older women without dementia . Further investigation is required to determine the etiology of these relationships Low frequency ( < 1 Hz ) delta EEG in sleep is of increasing interest as it indicates cortical reorganization , especially in the prefrontal cortex ( PFC ) . Other research shows that delta power in sleep is positively linked to waking cerebral metabolic rate . Such findings suggest that < 1 Hz activity may reflect waking performance at neuropsychological tests specific to the PFC . We investigated this unexplored area .  Sleep EEGs ( Fp1-F3 , Fp2-F4 , O1-P3 , O2-P4 ) were recorded in 24 healthy 61 - 75-year-olds . We found significant associations between 0.5 - 1.0 Hz power from the left frontal EEG channel , in the first non-REM period , and performance at tasks more specific to the left PFC ( e.g. , nonverbal planning and verbal fluency ) . This association was absent from the posterior channels . Neither age nor response times were confounding factors . This potential sleep EEG marker for PFC neuropsychological function in healthy , older people also points to further uses of the sleep EEG in underst and ing the role of sleep BACKGROUND Functional impairment in community-dwelling older adults is common and is associated with poor outcomes . Our goal was to compare the contribution of impairment in executive function or global cognitive function to predicting functional decline and mortality . METHODS We studied 7717 elderly women enrolled in a prospect i ve study ( mean age 73.3 years ) and identified women with poor baseline executive function ( score > 1 st and ard deviation [ SD ] below the mean on the Trail Making Test B ( Trails B ; n = 957 , 12.4 % ) , poor global cognitive function ( score > 1 SD below the mean on a modified Mini-Mental State Examination [ mMMSE ] , n = 387 , 5.0 % ) , impairment in both ( n = 249 , 3.2 % ) , or no impairment ( n = 6124 , 79.4 % ) . We compared level of functional difficulty ( Activities of Daily Living [ ADLs ] and Instrumental ADLs [ IADLs ] ) at baseline and at 6-year follow-up and survival at follow-up . We also determined if the association was independent of age , education , depression , medical comorbidities , and baseline functional ability . RESULTS At baseline , women with Trails B impairment only or impairment on both tests reported the highest proportion of ADL and IADL dependence compared to the other groups . At the 6-year follow-up after adjusting for age , education , medical comorbidities , depression , and baseline ADL or IADL , women with only Trails B impairment were 1.3 times more likely to develop an incident ADL dependence ( adjusted odds ratio [ OR ] = 1.34 ; 95 % confidence interval [ CI ] , 1.07 - 1.69 ) and 1.5 times more likely to develop a worsening of ADL dependence ( adjusted OR = 1.48 ; 95 % CI , 1.16 - 1.89 ) when compared to women with no impairment on either test . In addition , women with only Trails B impairment had a 1.5-fold increased risk of mortality ( adjusted hazard ratio [ HR ] = 1.48 ; 95 % CI , 1.21 - 1.81 ) . In contrast 
    Output:
    
Results suggest that multiple sleep parameters differ in the way they benefit or impair EF .
Parameters such as greater wake after sleep onset and lower sleep efficiency , in addition to circadian fragmentation of sleep , showed more consistent results and are potentially correlated with worsening in EF measures .
However , other results seem inconclusive .
Conclusion These findings were discussed based on the prefrontal circuitry vulnerability model , in which sleep has been identified as a beneficial factor for prefrontal cortex functioning and hence for EF , which relies mostly on this brain area and its related networks