Robert E. Dustman

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.

Differences in visually evoked responses in albino versus hoded rats

Abstract Single and summed visually evoked cortical responses of albino and hooded rats were compared before and after monocular occlusion or enucleation to determine if differences in optic tract terminations between strains of rats could be detected by variation in the electrical input recorded at the cortex. Peak latencies were earlier in the hooded than the albino rat under all conditions. The minimum flash intensity at which primary components appeared in the summed evoked response was lower for the albino than for the hooded rat. The response contralateral to the intact eye following enucleation was of much larger amplitude, although no differences were apparent in the background EEG. The ipsilateral response was more like the contralateral response in the hooded than in the albino rat. The latter finding is consistent with anatomical and behavioral reports.

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.

Visually evoked responses in the rat, guinea pig, cat, monkey, and man

Abstract Visually evoked responses were recorded, before and after enucleation of one eye, from the visual cortex of rats, guinea pigs, and cats, and from the scalp of stump-tailed monkeys and human subjects selected from a population of men who had lost one eye. The evoked response of each species was unique with certain distinguishing characteristics. However, the visually evoked responses of the the rat and guinea pig were similar as were those of monkey and man, although the monkey generally lacked the late afterdis-charge activity often seen in the human response. Changes in the waveform of the visually evoked responses recorded from each hemisphere following ocular enucleation varied among species. These changes could be related to the proportion of nondecussating optic fibers and anatomical differences of the visual systems of the various species.

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.

Age effects on heart rate, sustained potential, and P3 responses during reaction-time tasks.

Relationships between physiological responses and slowed reaction time (RT) among elderly subjects were tested in 48 healthy young, middle-aged, and elderly men (mean ages 24, 45, and 71 years) using simple and choice RT tasks. There were age reductions in P3 amplitude and heart rate (HR) deceleration, but no effects of age on P3 latency. Sustained potential (SP or CNV) amplitude paradoxically increased with age, possibly indicating weaker inhibitory function. P3 amplitude, SP amplitude, and HR deceleration were most strongly correlated with RT among younger subjects, but SP amplitude was correlated with RT in the elderly group during the choice task. HR deceleration shared a small amount of variance with SP amplitude and RT in the young group. There was no HR-SP-RT relationship in the older groups. Choice-simple task differences in P3 amplitude and RT were correlated in the young and elderly groups. The results suggest that HR, SP, and P3 responses may reflect physiological processes related to the slower RTs of healthy elderly subjects.

Effects of alcohol on visually evoked responses in rats during addiction and withdrawal

Abstract The time course of visually evoked responses (VERs) recorded at the cortex were studied in rats during addiction and withdrawal. Data for peak-to-peak amplitudes, latencies and photic afterdischarges (PhADs) were collected on the fifth, eleventh and seventeenth days of addiction, on the day of withdrawal and on the first, second and seventh days postwithdrawal. For the ethanol group during the addiction phase, amplitude and PhAD measures were depressed at the first recording session (day 5) and remained so throughout the addiction phase. Latency data, however, revealed a progressive increase to major peaks throughout the addiction phase that reached significance for P2 on day 17. VER amplitudes and PhAD excursion values were depressed and latencies increased, relative to controls, at the end of the addiction phase. On the day of withdrawal (day 0), P3-N3 amplitudes and PhAD excursion values remained significantly depressed relative to controls. Amplitude measures for other individual components had returned to control levels but had not yet exhibited rebound (neural hyperexcitability). Latency measures remained unchanged during day 0 testing and demonstrated a recovery to control levels by day 1 or 2 postwithdrawal. On day 1 postwithdrawal, amplitude and PhAD measures reflected neural hyperexcitability that remained throughout the seventh day although the decline in amplitudes between the second and seventh day of postwithdrawal testing suggested a trend toward neural recovery. The time course of VER amplitudes and latencies and the PhAD during addiction and withdrawal are discussed.

Naloxone-induced electrographic seizures in the primate

Electrographic seizure activity was recorded shortly following naxolone injections in artificially ventilated, methadone-treated stump-tailed macaques. Plasma-methadone concentrations prior to seizure activity were many times higher than those that have produced respiratory depression and death in nonventilated monkeys. The duration of seizure activity was clearly related to the dose of naloxone. Naloxone was without epileptogenic properties in animals that had not been pretreated with methadone. The results suggest that methadone and naloxone have additive epileptogenic properties when high blood levels of methadone are achieved in the artificially ventilated primate. Naloxone was devoid of antagonistic properties with respect to opiate-induced electroencephalographic spiking activity.

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.