Donald E. Shearer

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.

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.

Age differences in augmenting/reducing of occipital visually evoked potentials

Abstract Visually evoked potentials (VEPs) to 3 intensities of flash were recorded from 220 males aged 4–90 years. Amplitude-intensity slope measures of occipital VEPs revealed that most children were reducers, i.e., the amplitude of a middle latency wave attenuated in response to increased flash intensity. The tendency to ‘reduce’ VEP amplitude was strongest in the youngest children then rapidly decreased in strength with age so that by mean age 14 years they were predominantly augmenters, as were older individuals. Two groups of 15 children were studied further: those with the most negative slopes, reducers, and those with the most positive slopes, augmenters. Reducers had significantly larger VEPs than augmenters for dim flash conditions, thus supporting the theory that reducing is a CNS protective mechanism. However, reducers required significantly brighter flashes than augmenters for visual threshold determinations, suggesting that the tendency to augment or reduce sensory stimulation may be a basic perceptual phenomenon that governs the registration of even very weak stimuli. Analyses of single trial potentials (STPs) from which VEPs were averaged indicated that augmentation and reduction of VEP amplitude were more closely related to increased and decreased variability among STP wave forms than to intensity related changes in STP amplitudes. Individuals cannot be accurately classified as augmenters and reducers unless the area from which VEPs are recorded is specified since for some subjects, especially children, VEPs can augment at central scalp while reducing at occipital scalp.

Phencyclidine-induced alterations of rat electrophysiology

Phencyclidine (PCP) at high doses causes both excitation and depression in the rat. The visual evoked potential (VEP) was measured in rats following PCP administration in doses ranging from 1 mg/kg to 56 mg/kg. Consistent lengthening of VEP latencies suggests that PCP has an unusual inhibitory effect on visual function in the presence of the excitatory signs of bilaterally synchronous cortical spiking. The epileptogenic properties of PCP are quite evident in rats.

Aerobic Fitness May Contribute to CNS Health: Electrophysiological, Visual and Neurocognitive Evidence:

Relationships between aerobic fitness and CNS functioning, as defined by performance on neuropsychological and electrophysiological measures, were investigated in an exercise intervention study and in a cross-sectional study of young and older men with high and low fitness levels. The intervention study revealed that a 4-month walking program resulted in a 27% increase in maximum oxygen utilization (V02max) for previously sedentary 55-70 year old men and women. This increase in aerobic fitness was accompanied by significant improvement in response time, visual sensitivity, and performance on a battery of cognitive tests. The cross-sectional study showed: 1) that physically active older men could achieve and maintain V02max levels higher than those of sedentary men 30 years younger; 2) that aerobic fitness was generally associated with superior performance on measures of EEG, event-related potentials, visual sensitivity, and cognitive efficiency; and 3) that significant decrements in performance on ourelectrophysiological and neuropsychological measures had occurred by 50-62 years of age in healthy men. The positive relationships we observed between aerobic fitness and our dependent measures suggest that the practice of aerobic exercise may contribute to better CNS functioning, perhaps the result of exercise induced increases in cerebral oxygenation.

Methadone-induced changes in the visual evoked response recorded from multiple sites in the cat brain.

Visual evoked responses (VERs) and EEG were recorded following the i.p. administration of five doses of methadone (0.5–4 mg/kg) to 12 adult cats, which were implanted with cortical and subcortical electrodes. Additional cats, subjected to the same drug regimen, were used to evaluate plasma methadone concentrations. Doses of methadone that produced plasma concentrations between 80 and 190 ng/ml differentially affected VERs recorded from cortical and subcortical sites. Of the subcortical structures evaluated, the limbic system, specifically the hippocampus, was the most sensitive to the effects of the drug. These effects appeared to be primarily depressant. Responses recorded from the reticular formation and centromedian were affected only by the highest dose of methadone, while VERs recorded from cortical sites were reliably altered following the two highest doses and appeared to reflect both excitation and depression. Behavioral changes, however, were clearly evidenced in some cats at lower doses of methadone. Therefore, the data suggest (1) that those structures evaluated electrophysiologically did not reflect the full force of the drugs action as evidenced by its effect on behavior, (2) that cortical and subcortical recording sites have differential sensitivities, and (3) that one clearly defined, principal site of action of methadone is absent in the cat.

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.

Effects of dipropylacetic acid on late components of the photically evoked potential and afterdischarge in rat

The effects of dipropylacetic acid (DPA) on primary, secondary and afterdischarge waves of the photically evoked potential were examined. It was observed that DPA selectively attenuated late wave components and afterdischarge. A thalamic locus of action for these effects is postulated.

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.

Prolonged electrophysiological and behavioral alterations following a single injection of methadone in the cat.

Abstract Visual evoked potentials (VEPs), EEG, plasma methadone concentrations, blood gas values, and behavioral ratings were recorded periodically for 4 days following a single injection (4 mg/kg IP) of methadone in cats. Most measurements indicated a prolonged drug effect which lasted into the 4th day. Independent alterations of VEP component amplitudes suggested site-specific variations in the time-course of the drug effects. An early component, reflecting activity of classical ascending pathways, was quite resistant to the drug effects immediately following injection. Only after 31 hours was this component significantly attenuated. The amplitude approached predrug values at the time of final measurement. A late VEP component was quickly suppressed following methadone and returned to predrug values after 55 hours. Decreases in EEG frequency, on the other hand, evidenced no time-dependency following drug administration. All animals were behaviorally normal after 55 hours with no further evidence of mania. The results confirm the prolonged effects of methadone in a species known for its unusual and complex response to opiates. Sites within the visual system are apparently highly sensitive to the drug and are differentially altered over time following methadone injection. These alterations are, for the most part, correlated with plasma methadone concentration.