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.

Amplitudes of visually evoked potentials to patterned stimuli: age and sex comparisons.

Electrophysiological age and sex differences in visual pattern responsivity were investigated. Pattern reversal evoked potentials (PREPs) and visual evoked potentials (VEPs) to patterned and unpatterned flashes were recorded from 20 normal subjects in each of 4 groups: young females and males aged 25-35 years and older females and males aged 55-70 years. PREP waves N70-P100 and P100-N150 from the older women were significantly larger than those from subjects in the other groups; mean amplitudes for the young females, young males and older males were not different. A similar effect, unusually large potentials for the older women, was obtained for VEPs, but only for VEPs elicited by patterned flashes and recorded from occipital scalp, i.e., an area overlying visual cortex which is sensitive to lines and edges. Our findings suggest that the visual system of older females is unusually responsive to patterned stimuli.

Cerebrovascular accident alters P300 event-related potential characteristics.

P300 event-related potentials to counted (target) and uncounted (background) visual stimuli were recorded from subjects who had sustained either a right or a left middle cerebral artery cerebrovascular accident (CVA) and from appropriate normal control subjects. Subjects were asked to count target stimuli and to ignore non-target stimuli. Standard measurements of the amplitude and latency of P300 components as well as intercorrelations among P300 wave forms from 3 brain regions (Fz, Cz, Pz) were collected. Amplitudes of N1-P2 and N2-P3 components as well as overall amplitude of the ERP wave form were reliably reduced by a CVA, but component latencies were not significantly affected. The amplitude reduction associated with a CVA cannot be simply interpreted as evidence for reduced cognitive efficiency because overall amplitudes and intercorrelations between brain regions of CVA patients were reduced for both counted and uncounted stimuli. The intercorrelations between brain regions were particularly reduced if the CVA was localized in the right hemisphere. For CVA patients, reduced component amplitudes may reflect decreased cortical intercommunication associated with damage to subcortical brain structures.

Pattern reversal evoked potentials: age, sex and hemispheric asymmetry.

Binocular pattern reversal evoked potentials (PREPs) and EEG power were recorded bilaterally from occipital scalp of 50 boys and 50 girls aged 5-14. PREP latency was unaffected by either age or gender. Amplitudes, however, were consistently larger for girls than boys, with differences diminishing by adolescence. Significant electrophysiological asymmetries were also found; larger PREP amplitudes were measured at the right occipital electrode than the left for the two waves investigated. These asymmetries were apparent in both girls and boys across all ages, although they tended to diminish with maturation. EEG alpha asymmetry did not correlate with PREP amplitude asymmetry. PREPs elicited by half-field stimulation of 8 girls aged 9-10 years determined that 'paradoxical lateralization' of the half-field response was the same for both left and right half-fields, thus failing to account for the asymmetry of the full-field binocular response.

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.

Remote effects of cerebrovascular accidents: visual evoked potentials and electrophysiological coupling.

Performance on two electrophysiological tasks, EEG and VEP, of patients who had sustained either a right or left middle cerebral artery CVA was examined. The occurrence of a stroke disrupted electrophysiological functioning of brain regions beyond the ischemic focus of the CVA, and these remote effects persisted beyond the period of transient diaschisis. CVA reduced the electrophysiological concordance between brain regions as reflected in EEG coupling and VEP intercorrelation procedures, and the disruption was more severe if the CVA affected the right as opposed to left middle cerebral artery. Techniques for characterizing the abnormal event-related potentials of CVA subjects are reviewed, and some possible theoretical explanations of the functional communication and remote effects are offered.

Age-related decrements in Stroop Color Test performance.

Administered a modified Stroop Color-Word Test to 80 healthy males aged 21-90 years as part of a study of neuropsychological functioning. No age differences were demonstrated on simple reading tasks; however, significant age effects were observed for the color naming and interference tasks (ps less than .001). Ss in the oldest age groups (61-70 and 71-90 years) performed more slowly than younger individuals on both of these. Of a variety of tests administered, performance on the Stroop Test was most affected by age. Because impairment on Stroop color naming and interference tests appears to be a concomitant of normal aging, caution should be exercised when one is interpreting Stroop test results from older patients with suspected cerebral dysfunction.

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.