Auditory event-related potentials in well-characterized groups of children

Sixty-eight subjects ranging in age from 6 to 23 years were studied in an ‘auditory oddball’ event-related potential (ERP) paradigm. Our results replicate other studies, finding P3 as the most consistent component of ERPs since childhood, although great variability of this component was found in the 6-year-old group. Separate age/ERP component latency and amplitude linear regressions were computed for subjects 6–14 and 6–23 years old. Our data show in both groups a significant negative and positive correlation between age and P3 latency and N1-P2 amplitude respectively. The age/P3 latency slope for the subjects under 15 years old was −19.00 msec/year versus 8.15 msec/year for all subjects (6–23 years old). Our results indicate that P3 latency during childhood decreases with age, reaching an asymptote after or during the second decade of life. No curvilinear relationship between age and P3 latency was found over the child groups, although a significant curvilinear relationship was found over the entire age range.This study showed no significant gender differences in latency at any age group. However, in the adult group females showed significantly larger amplitudes than males.     

Effects of the menstrual cycle on auditory event-related potentials

Gonadal steroids (estradiol and progesterone) can alter neuronal functioning, but electrophysiological evidence in women is still sparse. Therefore, the present study investigated event-related potentials (ERPs) to neutral stimuli over the course of the menstrual cycle. In addition, associations between ERPs and salivary estradiol and progesterone concentrations were investigated. Eighteen young healthy women were tested at three different phases of their menstrual cycle (menses, and follicular and luteal phases). ERPs (i.e., the N1 and P2 components, reflecting cortical arousal and the orienting response, the N2, P3, and the Slow Wave (SW), reflecting controlled processing) were measured using two different paradigms. In the luteal phase, early ERPs reflecting the cortical arousal response were diminished in the first stimulus block indicating an attenuated orienting response. These changes were significantly correlated with estradiol as well as progesterone levels. As to the later ERP components, the N2 latency was shorter during menses compared to the other two phases. No menstrual cycle-associated changes were apparent in other late ERP components. In sum, this study documents changes in auditory ERPs across the menstrual cycle with the most prominent changes occurring during the luteal phase. Future ERP studies therefore need to be more attentive to the issue of menstrual phase when studying female subjects or female patients.     

Long latency auditory evoked potentials: intensity, inter-stimulus interval, and habituation

Experiment 1 elicited the P1, N1, P2, and N2 components of the long latency auditory evoked potential (AEP) using a 1000 Hz tone presented at 30, 50, or 70 dB SPL and 1-, 3-, or 5-second inter-stimulus intervals to assess the relative effects of the combination of these variables on component amplitude and latency. Four blocks of 16 tone presentations each were recorded from each subject to determine if changes in the AEP would occur because of short-term habituation. Both stimulus factors interacted significantly in a systematic fashion for the amplitude measures, with increases in latency also associated with increases in intensity and inter-stimulus interval. Only minor changes across the four trial blocks for either the amplitude or latency measures were observed over the various stimulus presentation conditions. Experiment 2 employed the same tone stimulus presented at 50 dB SPL and a 3-second inter-stimulus interval. Eight blocks of 64 trials were recorded from each subject on each day for four days to investigate long-term habituation effects. No substantial changes in any of the component amplitudes or latencies were obtained across the 32 trial blocks. It was concluded that intensity and inter-stimulus interval interact to determine AEP amplitude as well as latency values and that the constituent components do not change appreciably with repeated stimulus presentations, even after several days.     

Isometric strength and endurance during the menstrual cycle.

Seven healthy young women, 3 whom had been taking oral contraceptives, were examined during the course of 2 menstrual cycles to assess their isometric strength, their endurance during a series of 5 fatiguing isometric contractions at a tension of 40% MVC, and their blood pressures and heart rates during those fatiguing contractions. Two sets of experiments were performed, one in which the subject's forearm temperature was allowed to vary as a function of T A, and one with the muscle temperature stabilized by immersion of the forearm in water at 37 degrees C. During exposure to ambient temperatures, isometric strength and both the heart rate and blood pressure responses at rest and at the end of a fatiguing, sustained isometric exercise, were not significantly different during any phase of the menstrual cycle in any subject. In contrast, the isometric endurance in the women not taking oral contraceptives varied sinusoidally in all 5 contractions with a peak endurance midway through the ovulatory phase and the lowest endurance mid-way through the luteal phase of the menstrual cycle. The isometric endurance of the women taking oral contraceptives did not vary during their menstrual cycle. After stabilization of the temperature of the muscles of the forearm in water at 37 degrees C, the isometric endurance of the normal subjects showed a hyperbolic response with the maximal endurance at the beginning and end of their cycles, and the shortest endurance at mid-cycle. Here again, however, the isometric endurance of the women taking oral contraceptives did not vary after immersion of their forearms in the 37 degree C water.     

Depressive Symptoms and Oral Contraceptives

Of 261 women who completed a self-rating scale for measuring depression, 168 were taking oral contraceptives and 93 were using physical methods of contraception. Of the group of women taking oral contraceptives 6·6% were more severely depressed than any of the control group. There was a significant variation in the depth of depression related to the day of the menstrual cycle in the control group. This association was not found in the oral contraceptive group, where premenstrual depression was limited to the one or two days preceding menstruation.Women taking a contraceptive containing lynoestrenol 2·5 mg. and mestranol 0·075 mg. showed a significantly increased incidence of pessimism, feelings of dissatisfaction, crying, and tension, compared with women taking other oral contraceptives and the control group.     

Effect of sleep stage on somatosensory evoked potentials by median nerve stimulation

The effects of sleep stage on early cortical somatosensory evoked potentials (SEPs) and short-latency components elicited by median nerve stimulation were studied in 12 normal volunteers. The latency of P13 in the awake stage was not significantly different from that in any sleep stage. The latencies of N16, N20 and P20 were significantly prolonged while the amplitude of N20 was decreased during the non-rapid eye movement (NREM) sleep stage. P22, P23 and N24 components showed double peaks (P23a, P23b, N24a, N24b) during the NREM sleep stage in 6 subjects, while N24 showed a single peak and only P22 and P23 showed double peaks in 5 other subjects. The latencies and morphologies of SEPs during rapid eye movement sleep stage were almost the same as those during the awake stage. These findings suggest that NREM sleep affects the latency, amplitude and morphology of N16 and early cortical components.     

Altered haemorheology in oral-contraceptive users.

The haemorheological profile of the menstrual cycle was determined in 12 women who did not take oral contraceptives and compared with that in two groups of women (n = 8 and n = 30) who had been taking oral contraceptives for at last six months. Packed cell volume, platelet count, erythrocyte deformability, plasma fibrinogen concentration, and plasma and whole-blood viscosity varied cyclically throughout the menstrual cycle in the 12 non-users. This variation was abolished by the use of oral contraceptives, and the values of these indices were raised by an amount likely to predispose to thrombosis.     

Fatty acid reesterification but not oxidation is increased by oral contraceptive use in women.

We evaluated the hypothesis that fatty acid reesterification would be increased during rest and exercise in the midluteal menstrual cycle phase and during oral contraceptive use, when ovarian hormone concentrations are high, compared with the early follicular phase. Subjects were eight moderately active, weight-stable, eumenorrheic women (24.8 +/- 1.2 yr, peak oxygen consumption = 42.0 +/- 2.3 ml.kg(-1).min(-1)) who had not taken oral contraceptives for at least 6 mo. Plasma free fatty acid (FFA) kinetics were assessed in the 3-h postprandial state by continuous infusion of [1-(13)C]palmitate and [1,1,2,3,3-(2)H]glycerol during 90 min of rest and 60 min of exercise at 45% and 65% peak oxygen consumption in the early follicular and midluteal menstrual cycle phases and during the inactive- and high-dose phases following 4 mo of oral contraceptive use. Plasma FFA rates of appearance, disappearance, and oxidation increased significantly from rest to exercise with no differences noted between menstrual cycle or oral contraceptive phases or exercise intensities. Compared with either menstrual cycle phase, oral contraceptive use resulted in an increase in plasma-derived fatty acid reesterification and a decrease in the proportion of plasma FFA rate of disappearance that was oxidized at rest and during exercise. Endogenous and exogenous synthetic ovarian hormones do not exert a measurable influence on plasma FFA turnover or oxidation at rest or during moderate-intensity exercise in the 3-h postprandial state when carbohydrate use predominates. The increase in whole body lipolytic rate during exercise noted previously with oral contraceptive use is not matched by an increase in fatty acid oxidation and results in an increase in reesterification. Synthetic ovarian hormones contained in oral contraceptives increase lipolytic rate, but fatty acid oxidation during exercise is determined by exercise intensity and its metabolic and endocrine consequences.     

Influence of Menstrual Cycle Phase and Oral Contraceptive Use on the Time-of-Day Effect on Maximal Anaerobic Power

This study was designed to analyse the time-of-day effect in maximal anaerobic power, and the influence of menstrual cycle phase and oral contraceptive use on any diurnal effect. Diurnal variations in maximal cycling power were studied in 11 eumenorrheic women and 10 women using monophasic oral contraceptives. Subjects were tested at 09:00, 14:00 and 18:00 hours, assigned randomly on separate days, in the mid-follicular or pseudo-follicular phase (days 7, 8, 9) and in the mid-luteal or pseudo-luteal phase (days 19, 20, 21) of the menstrual cycle. The order of test sessions was randomly assigned. Body mass was measured before, and rectal temperature after, a standardized 15-min warm-up. Maximal cycling power (Pc) was determined by a force-velocity test. Rectal temperature significantly increased from morning (09:00) to afternoon (14:00 and 18:00) in follicular and luteal phases for eumenorrheic subjects, and in days 7–9 and days 19–21 for contraceptive users (p < 0.05). No significant interaction effects (time of day × group × cycle phase) were observed for rectal temperature. In eumenorrheic subjects, Pc increased significantly from 09:00 to afternoon during the follicular phase (P < 0.05). In contrast, no significant time-of-day effects were observed during the luteal phase in eumenorrheic subjects, and at any cycle phase in contraceptive users. Analysis of variance failed to reveal any significant interaction effects for Pc. This study suggested that the time-of-day effect on maximal anaerobic power could be damped during the luteal phase of eumenorrheic women or at any cycle phase by oral contraceptive use.     

Scalp-recorded short and middle latency peroneal somatosensory evoked potentials in normals: comparison with peroneal and median nerve SEPs in patients with unilateral hemispheric lesions

Peroneal somatosensory evoked potentials (SEPs) were performed on 23 normal subjects and 9 selected patients with unilateral hemispheric lesions involving somatosensory pathways.Recording obtained from right and left peroneal nerve (PN) stimulations were compared in all subjects, using open and restricted frequency bandpass filters. Restricted filter (100–3000 Hz) and linked ear reference (A1–A2) enhanced the detection of short latency potentials (P1, P2, N1 with mean peak latency of 17.72, 21.07, 24.09) recorded from scalp electrodes over primary sensory cortex regions. Patients with lesions in the parietal cortex and adjacent subcortical areas demonstrated low amplitude and poorly formed short latency peroneal potentials, and absence of components beyond P3 peak with mean latency of 28.06 msec. In these patients, recordings to right and left median nerve (MN) stimulation showed absence or distorted components subsequent to N1 (N18) potential.These observations suggest that components subsequent to P3 potential in response to PN stimulation, and subsequent to N18 potential in response to MN stimulation, are generated in the parietal cortical regions.     

Effects of aging on event-related brain potentials (ERPs) in a visual detection task

Event-related brain potentials (ERPs) were recorded from 74 subjects (45 men) between 18 and 82 years of age in a simple visual detection task. On each trial the subject reported the location of a triangular flash of light presented briefly 20° laterally to the left or right visual field or to both fields simultaneously. ERPs to targets exhibited a similar morphology including P1, N1, P2, N2, and P3 components across all age groups. The principal effects of advancing age were (1) a marked reduction in amplitude of the posterior P1 component (75–150 latency) together with an amplitude increase of an anterior positivity at the same latency; (2) an increase in amplitude of the P3 component that was most prominent over frontal scalp areas; and (3) a linear increase in P3 peak latency. These results extend the findings of age-related changes in P3 peak latency and distribution to a non-oddball task in the visual modality and raise the possibility that short-latency ERPs may index changes in visual attention in the elderly.     

Influence of menstrual cycle and oral contraceptives on tolerance to uncompensable heat stress

In this study we examined the influence of menstrual cycle phase and oral contraceptive use on thermoregulation and tolerance during uncompensable heat stress. Eighteen women (18-35 years), who differed only with respect to oral contraceptive use (n = 9) or non-use (n = 9), performed light intermittent exercise at 40 degrees C and 30% relative humidity while wearing nuclear, biological and chemical protective clothing. Their responses were compared during the early follicular (EF, days 2-5) and mid-luteal (ML, days 19-22) phases of the menstrual cycle. Since oral contraceptives are presumed to inhibit ovulation, a quasi-early follicular (q-EF) and quasi-mid-luteal (q-ML) phase was assumed for the users. Estradiol and progesterone measurements verified that all subjects were tested during the desired phases of the menstrual cycle. Results demonstrated that rectal temperature (Tre) was elevated in ML compared with EF among the non-users at the beginning and throughout the heat-stress trial. For the users, Tre was higher in q-ML compared with q-EF at the beginning, and for 75 min of the heat-stress exposure. Tolerance times were significantly longer during EF [128.1 (13.4) min, mean (SD)] compared with ML [107.4 (8.6) min] for the nonusers, indicating that these women are at a thermoregulatory advantage during the EF phase of their menstrual cycle. For the users, tolerance times were similar in both the q-EF [113.0 (5.8) min] and q-ML [116.8 (11.2) min] phases and did not differ from those of the non-users. It was concluded that oral contraceptive use had little or no influence on tolerance to uncompensable heat stress, whereas tolerance was increased during EF for non-users of oral contraceptives.     

Short-latency somatosensory evoked potentials following median nerve stimulation in Down's syndrome

Short-latency somatosensory evoked potentials (SEPs) following median nerve stimulation were recorded in 42 patients with Down's syndrome and in 42 age- and sex-matched normal subjects. There were no significant differences between the 2 groups in the absolute peak latencies of N9, N11 and N13 components. However, interpeak latencies, N9-N11, N11-N13 and N9-N13, were prolonged significantly in Down's syndrome. These findings suggest impaired impulse conduction in the proximal part of the brachial plexus, posterior roots and/or posterior column-medial lemniscal pathway. Interpeak latency N13-N20, representing conduction time from cervical cord to sensory cortex, was not significantly different between the 2 groups. Cortical potentials N20 and P25 in the parietal area and P20 and N25 in the frontal area were of significantly larger amplitude in Down's syndrome. P25 had double peaks in 16 of 42 normal subjects, but these were not apparent in any of the patients.     

Express Attentional Re-Engagement but Delayed Entry into Consciousness Following Invalid Spatial Cues in Visual Search

Background

In predictive spatial cueing studies, reaction times (RT) are shorter for targets appearing at cued locations (valid trials) than at other locations (invalid trials). An increase in the amplitude of early P1 and/or N1 event-related potential (ERP) components is also present for items appearing at cued locations, reflecting early attentional sensory gain control mechanisms. However, it is still unknown at which stage in the processing stream these early amplitude effects are translated into latency effects.

Methodology/Principal Findings

Here, we measured the latency of two ERP components, the N2pc and the sustained posterior contralateral negativity (SPCN), to evaluate whether visual selection (as indexed by the N2pc) and visual-short term memory processes (as indexed by the SPCN) are delayed in invalid trials compared to valid trials. The P1 was larger contralateral to the cued side, indicating that attention was deployed to the cued location prior to the target onset. Despite these early amplitude effects, the N2pc onset latency was unaffected by cue validity, indicating an express, quasi-instantaneous re-engagement of attention in invalid trials. In contrast, latency effects were observed for the SPCN, and these were correlated to the RT effect.

Conclusions/Significance

Results show that latency differences that could explain the RT cueing effects must occur after visual selection processes giving rise to the N2pc, but at or before transfer in visual short-term memory, as reflected by the SPCN, at least in discrimination tasks in which the target is presented concurrently with at least one distractor. Given that the SPCN was previously associated to conscious report, these results further show that entry into consciousness is delayed following invalid cues.     

Normative data on scalp responses evoked by infraorbital nerve stimulation

Normative data concerning the waves W1, W2, W3, P4, N5, P6 and N7 recorded from the scalp after stimulation of the infraorbital nerve have been collected from 96 healthy subjects, selected according to age and sex. Peak latency, inter-peak intervals, side-to-side asymmetry of inter-peak intervals, amplitude, amplitude ratio of some components versus W1 and side-to-side asymmetry of such ratio have been analysed as functions of age and sex. None of these parameters appeared to be affected by sex; computation of the correlation coefficient showed a significant (P < 0.01), though slight, increase of value of the inter-peak intervals W1–W2 and W1–W3 with age. This increase was partially confirmed by analysis of variance. However, such differences are too small to be useful for practical applications, so only a single normative value is proposed for each parameter. The influence of stimulus strength on the amplitude of the W1 component has been studied in 10 more subjects; amplitude saturation of this wave has been found to take place at intensities between 4 and 6 times the sensory threshold. Increasing the stimulus rate from 1 to 3 pulses/sec did not affect any of the components. It is remarked that components W1, W2, W3 and, to a lesser extent, P4 are the ones to be considered useful in clinical practice.     

Pain-related and cognitive components of somatosensory evoked potentials following CO2 laser stimulation in man

We recorded cortical potentials evoked by painful CO₂ laser stimulation (pain SEP), employing an oddball paradigm in an effort to demonstrate event-related potentials (ERP) associated with pain. In 12 healthy subjects, frequent (standard) pain stimuli (probability 0.8) were delivered to one side of the dorsum of the left hand while rare (target) pain stimuli (probability 0.2) were delivered to the other side of the same hand. Subjects were instructed to perform either a mental count or button press in response to the target stimuli. Two early components (N2 and P2) of the pain SEP demonstrated a Cz maximal distribution, and showed no difference in latency, amplitude or scalp topography between the oddball conditions or between response tasks. In addition, another positive component (P3) following the P2 was recorded maximally at Pz only in response to the target stimuli with a peak latency of 593 msec for the count task and 560 msec for the button press task. Its scalp topography was the same as that for electric and auditory P3. The longer latency of pain P3 can be explained not only by its slower impulse conduction but also by the effects of task difficulty in the oddball paradigm employing the pain stimulus compared with electric and auditory stimulus paradigms. It is concluded that the P3 for the pain modality is mainly related to a cognitive process and corresponds to the P3 of electric and auditory evoked responses, whereas both N2 and P2 are mainly pain-related components.     

Amenorrhoea after Discontinuing Combined Oestrogen-Progestogen Oral Contraceptives

Out of 210 women seen at the Middlesex Hospital with secondary amenorrhoea the 63 who developed it after stopping oral contraceptives were fully investigated. Five had organic disease sufficient to account for the amenorrhoea (one had severe diabetes, one a pituitary tumour, and three premature ovarian failure); two patients had galactorrhoea (one of whom also had the pituitary tumour); two had anorexia nervosa.Of the 63 women 40 (63%) had suffered from amenorrhoea or prolonged or irregular menstrual cycles before taking the pill, and this suggested that combined oestrogen-progestogen oral contraceptives should be used with caution for women with irregular menstruation.Nineteen patients wished to become pregnant and 12 have so far done so after treatment with clomiphene or gonadotrophins.In another study 204 women recorded when their first menstrual cycle occurred after stopping the pill. Seventy-four had a cycle longer than five weeks but only five exceeded three months, and only one of the five had more than six months'' amenorrhoea. These results confirm that the incidence of amenorrhoea after stopping oral contraceptives is low.     

Amplitude-time parameters of long-latency components (N1, N2 and P300) of acoustic evoked potential of healthy examinees of young and mature age

The aim of study was to track a cumulative changes of amplitude-time parametres of components N1, N2 and P300 of acoustic evoked potential in experimental situations different in complexity (at the account and listening of sounds) and to compare the received distinctions at examinees of young and mature age. ERP were recorded at 12 healthy subjects from 18 to 22 ages and 12 subjects from 32 to 59 ages. The two-stimuli oddball paradigm was used. It is revealed that components N1, N2 and P300 recorded in the situation of the listenings of sounds without any preliminary instruction do not differ at persons of young and mature age. At examinees of younger age the biger amplitude of component N1 is noted at the account of sounds in comparison with listening whereas the latency of the one do not change depending on complexity of the task. It is shown that component N2 has stability of latency in relation to age and an experimental situation. The amplitude of component N2 is above at the account of sounds in both age groups. The amplitude-time parametres of component P300 do not differ at examinees of different age in a problem of listening of sounds. The revealed features of components N1, N2 and P300 at examinees of young and mature age in experimental situations different in complexity, allow to assume that with the years at the person adaptive mechanisms which allow carrying out successfully of the task.     

Pattern ERG: effects of reference electrode site,stimulus mode and check size

We studied monocular pattern ERG (PERG) in 10 normal subjects and a patient with optic neuritis. No clinically significant PERG could be recorded from the occluded eye with any reference (ipsilateral ear or temple, or midfrontal), indicating that cross-contamination is not present with binocular testing. Ipsilateral temple reference minimized VEP (P100/N100) contribution to the PERG N95 which occurred with ipsilateral ear or midfrontal reference. The conclusions were confirmed by results from the patient, who had marked monocular delay of a normal amplitude P100. Twenty-four subjects were tested with monocular and binocular stimulation using an ipsilateral temple reference. There were differences in PERG latencies and amplitudes although the interside amplitude ratio showed smaller differences with binocular stimulation. Increasing check size (17, 35 and 70 min) decreased P50 and N95 latencies and increased P50 amplitude.     

ERPs to subclasses of nouns and verbs

The present findings show the existence of significant differences in latency and amplitude of some waves of ERPs to three subclasses of nouns or verbs. Latency LP3 of ERPs to action verbs was shorter than latency of the same wave to abstract verbs. In nouns the relation was a similar (manipulable objects versus abstract ones). The amplitude of early positive components (P1, P2) and BN3 wave also depended on semantic attributes of nouns and verbs. Some waves of ERPs to motion verbs in our experiment had significantly higher amplitude than the same waves of ERPs to nonmanipulable objects. Also revealed was interaction between some ERP features and the subject's gender. It was primarily the amplitude of BP2, the size of which depended on gender in all cases--BP2 amplitude was significantly higher in females then in males. In the other components (BP1, BP4, BN2 and BN4) there were fewer significant differences and if they do occurred, then their amplitude was higher in males than in females. In some cases, gender also affected latency of waves LP2, LN1 and LN4 of ERPs to the same noun or verb subclass--latencies of these waves were shorter in females.