Life-span changes in EEG spectral amplitude, amplitude variability and mean frequency.

OBJECTIVES: The objectives were to assess life-span alterations in intrasubject variability of EEG spectral amplitudes and in amplitude and mean frequency computed from spectral amplitude profiles. METHODS: EEG was recorded from the central and occipital scalp of 222 healthy males aged 4 to 90 years. Amplitude spectral profiles derived from FFT procedures provided data for the computation of amplitude variability (ampCV), absolute and relative amplitude and mean frequency for each of five spectral bands. Analysis of variance, coefficient of correlation and t test were employed in data analyses. RESULTS: The ampCV measure did not provide direct evidence of age-related intrasubject changes in EEG frequency but was useful for indexing the presence of rhythmic EEG activity. Marked decreases in absolute amplitude occurred during childhood with little change thereafter. Age changes in relative amplitude were more complex and differed for slow and fast EEG activity. We also report that an algorithm frequently used to estimate mean frequency can introduce consistent bias into mean frequency computations under some conditions. CONCLUSIONS: Life-span changes in measured EEG characteristics were generally consistent with those from earlier studies. It is important that investigators validate and describe procedures used to determine mean frequency of EEG spectral data.

Life span changes in electrophysiological measures of inhibition.

Three electrophysiological findings which provide suggestive evidence of weakened inhibition in children and the elderly are reviewed. First, compared to young adults, electrophysiological recordings from old adults show a greater incidence of EEG alpha in anterior cortical areas and of somatosensory evoked potentials in occipital areas, and a reduction in heterogeneity of EEG and ERP activity across recording sites. These findings suggest a relative weakening of central inhibition in old age and a loss of functional independence of cortical centers. Second, visually evoked potentials from children and the elderly demonstrate a relative lack of differentiation between patterned and unpatterned stimuli. Inhibition is known to be important within the visual system for the detection of lines and contours. Finally, children and the elderly do not dampen (inhibit) their electrophysiological responses to sensory stimuli as effectively as subjects of an intermediate age. These age-related differences in electrophysiological responsivity appear to parallel age changes in behavioral measures which are also believed to reflect weakened inhibition. The electrophysiological measures, which reflect maturity and health of CNS structural and chemical systems, indicate that inhibition plays an increasing role in the shaping of behavior as children approach late adolescence but a diminishing role as adults live beyond the fifth decade. Recent research, however, suggests that the magnitude of inhibitory loss in old age may be related to cardiovascular health. Older men who frequently participated in vigorous physical activity showed significantly less inhibitory loss than age-matched peers who seldom exercised.

Pattern reversal evoked potentials: gender differences and age-related changes in amplitude and latency.

This report is intended to complement the current body of literature by describing pattern reversal evoked potential (PREP) component amplitudes and latencies in a larger sample than has been previously studied and providing comparisons of males and females across the lifespan. Binocular PREPs were measured from 406 normal subjects, 6-80 years of age. In general, latencies were found to decrease during maturation, stabilize across early adulthood, then begin to increase sometime after the late 20s. There were minimal gender differences in latencies during development but males tended to have longer latencies than females during adulthood. Across the lifespan, amplitudes were larger for females. Results of regression analyses using the entire data set were compared to results of separate regression analyses for developmental years (6-20) and adulthood (21-80). Separate analyses appear to provide more useful descriptions of PREP latency and amplitude changes across the lifespan. It is clear that predicted normal values can vary depending on age range and relative proportion of males and females comprising a reference sample. Appropriate clinical values should be based on age- and sex-matched normal subjects and should be specific with regard to technical and methodological variables.

The effects of videogame playing on neuropsychological performance of elderly individuals.

To determine the effects of sensory-perceptual stimulation (videogame playing) on neuropsychological performance, measures of reaction time (RT), visual sensitivity, cognition, and affect were obtained from 60 healthy 60- to 79-year-old individuals before and after their 11-week participation in videogame (VG) playing, movie viewing, or as controls. Only RT demonstrated an activity specific change, being significantly faster at posttesting for the VG subjects. The RT results indicate that the central nervous system of elderly people can be modified by activation procedures. We speculate that VG playing may improve efficiency of cell assemblies stimulated by visuomotor activities common to both VG playing and RT.

Aerobic capacity of older adults: a training study.

The effects of a four month aerobic conditioning program on heart rate, blood pressure, maximal oxygen consumption (VO2max), and physical work capacity of 55-70 year old sedentary individuals were evaluated. Twenty-eight men and women participated in either 4 months of supervised fast walking or jogging at a prescribed target heart rate or stretching exercises for one hour, three days per week. Gains in VO2max (ml/kg/min) obtained during a Balke maximal treadmill test in aerobic and exercise control subjects were 27% and 9%, respectively. At posttesting subjects in both groups demonstrated improved maximal work rate, increased treadmill time, and experienced lower resting and recovery heart rates, lower resting systolic blood pressure, and fewer premature ventricular depolarizations during exercise testing. In 67 physician-supervised maximal exercise tests, only one subject did not achieve VO2max due to exercise induced arrhythmias. No events of morbidity or mortality occurred as a result of the exercise testing and training. Subjects were contacted 4 years after study participation to determine if they were adhering to an exercise program. Sixty-four percent reported exercising at least 3 days per week in large muscle activities. We conclude that four months of supervised aerobic and nonaerobic exercise training is sufficient to improve aerobic capacity and other indicators of fitness in older, sedentary men and women, and that these previously sedentary people are likely to continue exercising on an individual basis once they have experienced improved physical capacity.

Age and fitness effects on EEG, ERPs, visual sensitivity, and cognition.

Measures of EEG, event-related potentials (ERPs), visual sensitivity, and cognition were obtained from 30 young (20-31 years) and 30 older (50-62 years) healthy men. Age groups were evenly divided between subjects with low and high fitness levels documented by VO2max during a maximal exercise test. Age comparisons revealed that, compared to young adults, the older men had reduced visual sensitivity, delayed ERP latencies, greater homogeneity of EEG activity across recording sites, more positive visual-evoked potential (VEP) amplitude-intensity (A/I) slope, and poorer performance on a battery of neurocognitive tests. The EEG and VEP A/I slope findings are believed to reflect weakened central inhibition for the older men. In general, the measures that differentiated groups on the basis of age were also sensitive to differences in aerobic fitness. Compared to low fit men, the physically active men had shorter ERP latencies, stronger central inhibition, better neurocognitive performance, and better visual sensitivity. We speculate the performance superiority of the physically active men was, at least in part, the result of more oxygen being available for cerebral metabolism.

P3 latency and symbol digit performance correlations in aging.

Relationships among age, P3 latency, and Symbol Digit Modalities Test (SDMT) performance were investigated for 172 subjects ranging from 20 to 79 years. Age-related increases in P3 latency were most evident for older normal subjects (greater than 55 years) and for a subset of subjects with low physical fitness levels, but were negligible for a subset of subjects with high physical fitness levels. A similar relationship was found between age and SDMT. P3 latency and SDMT performance were significantly correlated for older subjects with low fitness levels but not for young (less than 55 years) subjects or subjects with high fitness levels. Partial correlation analyses indicated a significant relationship between P3 latency and SDMT performance that was independent of age. These results agree with previous studies suggesting that P3 latency provides a sensitive measure of age- and/or health-related processes affecting CNS function and cognitive performance. Careful attention to nonpathologic subject variables and use of age-adjusted norms are important considerations for clinical use of P3 latency.

Cardio-respiratory fitness of young and older active and sedentary men.

Physiological profiles are described for 30 healthy young (20-31 years) and 30 healthy older (50-62 years) men. Half of the individuals in each group reported that during the previous five years they participated frequently in strenuous physical exercises; the other half reported sedentary lifestyles. A treadmill exercise test was used to determine maximal aerobic power (VO2 max). Heart rate and blood pressure were measured during rest, maximal exercise and recovery. The active older men demonstrated significantly lower resting heart rates, lower resting systolic and diastolic blood pressures, higher VO2 max, lower maximal exercise diastolic blood pressure and lower recovery heart rates than the age-matched sedentary men. Compared with the young sedentary men, the older active men had lower resting heart rates and higher VO2 max, walked longer on the treadmill, had lower recovery heart rates and weighed less. Older active men also had higher VO2 max levels than young sedentary men. In summary, physiological profiles of the older active men more closely resembled profiles of active men who were 30 years younger than those of older sedentary men. These results emphasize the range of benefits associated with exercise.

Neuropsychological performance of young nondrinkers, social drinkers, and long- and short-term sober alcoholics.

Neuropsychological performance of 23-42-year-old males with diverse drinking histories was assessed. Comparisons were made among nondrinkers, social drinkers, short-term sober (less than 30 days) alcoholics and long-term sober (greater than 30 days) alcoholics. Results of these comparisons provided little support for the notion that neurotoxic effects of chronic alcohol consumption are directly related to cognitive impairment. Instead, these results suggested that performance differences among the groups were more closely related to subclinical withdrawal symptoms or native ability than to long-term alcohol consumption. Because none of the dependent measures was related to length of abstinence, and because Wechsler's Adult Intelligence Scale-R Vocabulary differences among groups paralleled neuropsychological test performance differences, it is suggested that differences among groups may reflect differences in native ability. In addition, there were no differences between social drinkers and nondrinkers, nor were there any significant correlations among drinking variables and performance of social drinkers, providing further evidence against a direct relationship between alcohol consumption and cognitive performance.

EEG, visually evoked and event related potentials in young abstinent alcoholics.

EEG, visually evoked potentials (VEP), and event related potentials (P300) were recorded from 60 males aged 25-40 (20 abstinent alcoholics, 20 social drinkers, and 20 lifetime nondrinkers). Alcoholics were at least 1 month abstinent, medication free, and neuropsychologically normal. Residual effects of alcohol abuse were not detected in EEG power and cortical coupling analyses, or VEP amplitude, latency, and amplitude/intensity slope measures. Only P300 measures, recorded while subjects were actively engaged in a visual oddball task (20% targets), differentiated alcoholics from nonalcoholics. Alcoholics had reduced N2-P3 amplitude and delayed N2 latencies compared to social drinkers and nondrinkers. Because P300 abnormalities have been reported for individuals with positive family history for alcoholism, it is not clear whether these results reflect familial influence or residual effects of alcohol abuse. Issues relating to age, health and medication status of abstinent alcoholics, and use of social drinkers as comparison groups in studies of brain dysfunction in "recovering" alcoholics are also discussed.

The effect of age, sex and interstimulus interval on augmenting and reducing of occipital VEPs.

Three intensities of patterned and unpatterned flashes were used to elicit occipital visually evoked potentials (VEPs) from 4 groups of 15 subjects: boys and girls aged 7-9 years and boys and 15 girls aged 13-15 years. Interstimulus intervals (ISIs) of 1, 2 and 4 sec were used. Amplitude/intensity (A/I) slope was computed for each ISI and flash type condition and an estimate was made of the ability to differentiate patterned from unpatterned stimuli. The latter was inferred from coefficients of correlation which reflected the degree of similarity between VEP wave forms elicited by the two types of flashes. Responses of younger children attenuated to increasing stimulus intensity (negative A/I slope), while VEP amplitude of older subjects augmented to brighter flashes. VEP amplitude reduction may be the response of an immature brain to overstimulation. Amplitude reducing by 7-9-year-old children does not appear to be related to insufficient time between flashes for visual system recovery, since ISI did not differentially affect A/I slope of the younger and older subjects. Longer ISIs did, however, tend to produce more positive A/I slopes for all subjects, but only for patterned stimuli, suggesting that pattern detectors do not fully recover with ISIs of 1 and 2 sec. The visual system of young children was relatively less efficient than that of older children at differentiating patterned from unpatterned stimuli, indicating a differential sensitivity of pattern detectors as a function of age. Gender was not a factor in either magnitude of A/I slope or similarity of VEP wave forms.

Power spectral analysis and cortical coupling of EEG for young and old normal adults.

Power spectral analysis and cortical coupling were computed on eyes closed EEG recorded from 80 normal volunteers: 20 females and 20 males aged 25-35 years and 20 females and 20 males aged 55-70 years. Recordings were from Fz, Cz, C3, Pz and Oz areas. The results indicate that with increased age there was a greater uniformity of EEG activity across the brain. Magnitude of EEG power was significantly less variable across recording sites for the old than for the young. In addition, cortical coupling values were reliably higher for the older subjects indicating a greater congruity among EEG patterns. The EEG power and cortical coupling measures were significantly correlated and thus may indicate an underlying mechanism common to both. The results support a theory of decreased central inhibitory function in old age and may reflect an age-related breakdown of functional autonomy of cortical areas. Gender had no significant effect on either EEG power or cortical coupling.

Aging and respond-withhold tasks: effects on sustained potentials, P3 responses and late activity.

Differences in late event-related potentials (ERPs) during active respond-withhold tasks were tested with 16 young, 16 middle-aged, and 16 elderly subjects (mean ages were 30, 50 and 69 years, respectively). All subjects were selected for good health. While monopolar electroencephalograms were recorded from FZ, CZ, and PZ, subjects performed a signaled respond-withhold task to allow measurement of sustained potentials (SPs) and a non-signaled respond-withhold task for measurement of P3 responses and late activity (LA) which follows the P3. Respond and withhold trials were presented randomly with a probability of 0.5 in both tasks. Compared with younger subjects, the elderly group produced significantly larger negative mean SP amplitude during respond trials at CZ, significantly larger negative mean LA during respond trials at CZ, and significantly larger positive LA during withhold trials at all electrode locations. The elderly group also produced significantly larger P3 amplitude at FZ. The results are discussed in relation to the hypothesis that inhibition may be weaker in elderly subjects. Two further possible interpretations of the larger ERPs in elderly subjects are suggested: (1) the elderly group may have been more challenged by the tasks and their larger ERPs may reflect greater neural effort; and/or (2) the health selection procedures may have produced a group of elderly 'survivors' whose large ERPs may be characteristic of robust individuals or may reflect adaptations to aging-related changes in neural function.

Naloxone-induced augmentation of the photically evoked afterdischarge in conscious rats.

Naloxone, at subconvulsive dose levels, from 1 to 15 mg/kg were administered to conscious rats. Significant increases in photically evoked afterdischarge occurrence were seen at naloxone dose levels above 5 mg/kg with no clinical evidence of seizure activity being observed. Typically photically evoked afterdischarge augmentation is only observed following the administration of convulsive drugs.

The effects of renal hemodialysis on pattern reversal evoked potentials.

PREP P100 latency was significantly prolonged in patients maintained on renal hemodialysis. P100 latency also failed to show changes related to time past dialysis. PREPs may be of use in evaluating the progression of uremic induced dysfunction.

Aerobic exercise training and improved neuropsychological function of older individuals.

The effects of a four month aerobic exercise conditioning program on neuropsychological test performance, depression indices, sensory thresholds, and visual acuity of 55-70 year old sedentary individuals were evaluated. Aerobically trained subjects were compared with two age-matched control groups of subjects: those who trained with strength and flexibility exercises and others who were not engaged in a supervised exercise program. The aerobically trained subjects demonstrated significantly greater improvement on the neuropsychological test battery than did either control group. Depression scores, sensory thresholds, and visual acuity were not changed by aerobic exercise. The pattern of results suggests that the effect of aerobic exercise training was on central rather than on peripheral function. We speculate that aerobic exercise promoted increased cerebral metabolic activity with a resultant improvement in neuropsychological test scores.

Pattern reversal evoked potential amplitudes: life span changes.

Pattern reversal evoked potentials (PREPs) were recorded from people whose ages ranged from 4 to 90 years. Dramatic reductions in PREP amplitudes occurred between childhood and adolescence. These changes were most evident in females. Following adolescence there were no significant changes in amplitudes, even to old age. Latencies, on the other hand, have been shown to change most dramatically between adulthood and old age. PREP amplitudes and latencies, therefore, appear to provide different and unique information regarding development and aging. One cannot ignore PREP amplitudes without sacrificing information regarding early development.