Response properties of long-latency event-related potentials evoked during NREM sleep

The experiments reported here sought to investigate whether the K-complex evoked during sleep is comprised of activity from two separate physiological systems with different response properties. To that end, the parameters of stimulation in a two tone auditory 'odd-ball' task were varied systematically as stimuli were presented to subjects during NREM sleep. During experiment 1, the frequency (pitch) of the odd-ball stimulus varied systematically while intensity (loudness) was matched between tones. During experiment 2, pitch was matched between tones while the loudness of the odd-ball stimulus was varied. The long-latency event-related potentials (ERPs) N2 and P3 could be dissociated from the K-complex (N3 and P4) in response to these parametric manipulations. Information processing occurs during sleep, and is reflected in ERPs with a morphology largely analogous to those observed under similar conditions while subjects are awake. The second (K-complex) system is sleep specific. A model was constructed to explain the activity of these two hypothesized systems. As predicted by the model, K-complex latency was longer in Stage 2 when N2 and P3 were also active, than in Stage 4 where N2-P3 activity was lessened. These results support the two-system hypothesis; electrical brain activity evoked during sleep should not be considered a unitary sleep-specific response. Furthermore, the data indicate that the K-complex is sensitive to the physical characteristics of stimuli, that the sleeping brain processes information to a high degree, and that the 'endogenous' components of the ERP observed in awake humans reflect more automatic processes than previously suspected.     

Processing of auditory stimuli during tonic and phasic periods of REM sleep as revealed by event-related brain potentials

SUMMARY The brain has been reported to be more preoccupied with dreams during phasic than during tonic REM sleep. Whether these periods also differ in terms of the processing of external stimuli was examined. Event-related brain potentials (ERPs) to a frequent standard tone of 1000 Hz ( P = 97%) and infrequent deviant tones of 1100 and 2000 Hz ( P = 1.5% for each) were recorded ( n = 13) during wakefulness and nocturnal sleep. An ERP wave (called REM-P3) resembling a waking P3 wave was larger for the 2000 Hz deviant during tonic than during phasic REM sleep. Also the P210 wave was larger during tonic than during phasic REM sleep. A reliable mismatch negativity component appeared only in wakefulness. In summary, these results support the hypothesis that the brain is more 'open' for changes in an auditory input during tonic than phasic REM sleep.     

Auditory and somatosensory event-related brain potentials in early blind humans

Previous event-related potential (ERP) studies have suggested a possible participation of the visual cortex of the blind in auditory processing. In the present study, somatosensory and auditory ERPs of blind and sighted subjects were recorded when subjects were instructed to attend to stimuli of one modality and to ignore those of the other. Both modalities were stimulated with frequent (standard) and infrequent (deviant) stimuli, which differed from one another in their spatial locus of origin. In the sighted, deviant stimuli of the attended modality elicited N2 type of deflections (auditory N2b and somatosensory N250) over the lateral scalp areas. In contrast, in the blind, these ERP components were centroposteriorly distributed, suggesting an involvement of posterior brain areas in auditory and somatosensory stimulus discrimination. In addition, the mismatch negativity, elicited by deviant auditory stimuli even when the somatosensory stimuli were attended, was larger in the blind than in the sighted. This appears to indicate enhanced automatic processing of auditory stimulus changes in the blind. Thus, the present data suggest several compensatory changes in both auditory and somatosensory modalities after the onset of early visual deprivation.     

Auditory event-related potentials in humans and rats: effects of task manipulation

The purpose of this study was to compare components of the rat and human auditory event-related potential (ERP) as generated in active oddball and passive single-stimulus tasks. The rats were trained to discriminate between target and standard stimuli in an oddball task, whereas the human subjects received instructions. Task effects on various ERP components were found in both species. Interestingly, effects on the P3 component were similar in the species with regard to amplitude: Target stimuli elicited a higher amplitude in the oddball task than did standard stimuli. This might indicate that the P3 shares the same characteristics between species. However, the first four components occurred 1.82 times earlier in rats than in humans, expecting a P3 of about 200 ms in rats. The P3 in rats appeared at 380 ms. We conclude that either the relation between human and rat peak latencies is not linear, or the P3 in rats is not the equivalent of the human P3.     

Individual differences discriminate event-related potentials but not performance during response inhibition

Event-related brain potentials (ERPs) were recorded from 20 normal participants while they completed a Go/NoGo response inhibition task. Previous ERP studies have implicated the N2 and P3 waveforms as the main indices of processing in this task, and functional brain imaging has shown parietal, prefrontal and anterior cingulate cortices to be involved in response inhibition. 32-channel ERP analysis revealed amplitude differences in the N2/P3 components when stimuli that required a button-press (Go stimuli) were compared with stimuli for which the response had to be withheld (No-Go stimuli), and in N2 and P3 latencies when successful withholds to No-Go stimuli were compared with unsuccessful attempts to inhibit. Further differences in the N2/P3 complex emerged when participants were grouped in terms of a measure of absentmindedness (the Cognitive Failures Questionnaire, CFQ); larger and earlier components were found for high CFQ respondents. We conclude that the latencies of the N2 and P3 may be the critical indicators of active inhibitory processes for this task, suggesting that a pattern of sequential activation rather than altered activity level in key structures may mediate success on the task. In addition, highly absentminded participants exhibited larger components for errors than did less absentminded participants when performing at the same level, which implies that the absentminded may require greater activity in the neural substrates of response inhibition in order to accomplish this task at a comparable level of performance to less absentminded participants.     

The relationship between poor sleep and inhibitory functions indicated by event-related potentials

The present study focused on the relationship between normal variations of sleep and inhibitory functions as reflected in event-related potentials. For this reason one night of 21 healthy participants was analysed. After waking up all participants completed a visual Go/Nogo task. On the basis of a sleep disturbance index (SDI) the participants were separated into 8 SDI-good and 13 SDI-poor sleepers using a cluster analysis. The results showed that Nogo-N2 amplitude was smaller and Nogo-P3 latency longer in SDI-poor sleepers. Moreover, Go-P3 amplitude was smaller in SDI-poor sleepers. Performance parameters were not influenced by poor sleep. We concluded that poor sleep specifically affects the intensity of pre-motor inhibitory processes (Nogo-N2 amplitude), the speed to inhibit a motor response (Nogo-P3 latency) and the intensity of task-relevant information processing (Go-P3 amplitude). In further studies, it should be explored under which conditions such subliminal deficits also become relevant for overt behaviour.

Visual event-related potentials and depression in the elderly

Event-related potentials (ERPs) were recorded during a visual discrimination task from nine elderly individuals (mean=68.1 years), diagnosed as having major depressive disorder, and nine age-matched controls (mean=68.0 years). During the task, subjects pressed a switch to targets (the number 9) and ignored background (the number 6) and novel stimuli (random designs). Novel and target stimuli were both interspersed infrequently in the sequence of background stimuli. Scalp electrical activity was recorded from midline frontal (F_z), central (C_z), and parietal (P_z) sites. Depressives were characterized by lengthened response times and increased number of errors across the session. Speed of response was also found to vary directly with clinical status. Additionally, ERP correlates of depression in the elderly were found: N₁ was more prolonged for target than non-target stimuli in the depressed group; P₂ was larger for all conditions; N₂ was uniformly small across the scalp, whereas the controls showed small N₂ amplitudes only at F_z; large P₃s appeared in trials following the novel stimuli in the depressed but not in the control group. These results are interpreted in terms of the symptomatology associated with depression (i.e., distractability, impaired short-term memory or concentration, indecisiveness) and possible age-related changes in the ERP scalp distribution.     

The role of the spindle in human information processing of high-intensity stimuli during sleep

Sleep spindles are 12-14 Hz oscillations in EEG, which are thought to inhibit or 'gate' information processing. Event-related potentials may be employed to probe the extent of information processing during sleep. Previous research indicates that event-related potentials elicited by moderate intensity stimuli show increased positivity (or further removal of negativity) when stimuli are presented concurrent with spindles. However, the effectiveness of spindles to inhibit the processing of much louder stimuli remains unknown. The purpose of the present study was to investigate the extent of this gating, by using a range of stimuli including those that are loud and intrusive. Eight good sleepers were recorded during a single night. Auditory stimuli were delivered randomly at 0, 60, 80 or 100 dB SPL. Trials were sorted off-line by sleep stage, stimulus intensity and spindle characteristic (i.e. spindle absent, spindle present). During the sleep-onset period, the often-reported changes in event-related potentials were observed - N1 decreased and P2 increased in amplitude. In Stage 2 sleep, P2 was affected by the presence of spindles, particularly when stimulus intensity was loud. Its amplitude was greatest when spindles occurred following the onset of the stimulus. Scalp-recorded spindles might, therefore, be a consequence of the prior thalamic inhibition of information processing, especially when confronted by loud, intrusive external stimuli.     

Changes in the scalp topography of event-related potentials and behavioral responses during the sleep onset period

Event-related potentials (ERPs) and behavioral responsiveness were investigated during the transition from wakefulness to sleep. Ten participants were presented with an auditory oddball task during repeated sleep onset periods. The EEG was recorded from 29 different scalp sites. A 1500-Hz tone pip was presented infrequently (p = .04) within a series of lower pitch 1000-Hz "standard" stimuli (p = .96). Participants were required to button press upon detection of the rare "target" stimulus. During wakefulness, almost all targets were detected. A large amplitude P300 was observed to these detected targets. This P300 was maximum over parietal areas of the scalp. During stage 1 sleep, subjects continued to respond on 47% of trials. The parietal P300 amplitude remained large to these detected targets. It was, however, much attenuated at frontal sites. When the participant failed to detect the target in either stage 1 or 2, no P300 was visible. P300 is thus associated with behavioral detection of the target stimulus, whether in wakefulness or stage 1 "sleep." Trials were also sorted by reaction time (RT), in which bins 1-3 represented increasingly long RT. In the waking state, P300 amplitude did not significantly vary across the different bins. Although mean RT latency varied by 512 ms from bin 1 to bin 3, P300 latency varied by only 25 ms. Differences in RT are thus probably due to response-related processes rather than stimulus classification time.     

Motor and nonmotor event-related potentials during a complex processing task

Identification of the necessary stimulus properties to elicit the stimulus preceding negativity (SPN) has been the impetus for numerous research studies. The current study was conducted to explore the possibility that the SPN is an index of cognitive resource allocation. An auditory warning stimulus (S1) indicated whether an easy or difficult discrimination would occur at S2. The SPN was collected before a nonmotor discrimination task (S2) that consisted of identifying the higher of two bars. To eliminate the influence of motor processing prior to S2, a button press on the side of the higher bar was held until perception of a response cue (S3). Additionally, P3, contingent negative variation (CNV), and behavioral measures were collected to assist in assessing the SPN. Results indicated that although the SPN exhibited increased negativity, no differences were observed based on task difficulty. However, task difficulty did affect P3 data for both the warning tone and the discrimination task, an effect not observed for the CNV. Overall, the data did not support that hypothesis that the SPN provides an index of cognitive demand.     

Heritability of event-related brain potentials in families with a history of alcoholism

Event-related brain potentials (ERPs) are altered in patients with a variety of psychiatric disorders and may represent quantitative correlates of disease liability that are more amenable to genetic analysis than disease status itself. Estimates of heritability are presented for amplitude and latency of the N1 and P3 components of the ERP measured at 19 scalp locations in response to visual and auditory stimuli for 604 individuals in 100 pedigrees ascertained as part of the Collaborative Study on the Genetics of Alcoholism. Significant heritabilities were found for visual P3 amplitude in response to all stimuli and for visual P3 latency in response to target and novel, but not non-target, stimuli. Heritability of visual N1 latencies was uniformly low, whereas heritability of visual N1 amplitude was significant for all electrodes in response to the non-target stimuli but only for posterior electrodes in the other two stimulus conditions. Heritabilities for auditory target P3 were similar to those of the visual stimuli, with auditory target P3 amplitudes and latencies both demonstrating significant heritability. For auditory P2 in response to non-target stimuli, peak amplitude was heritable, but latency was not. Auditory N1 amplitude and latency were significantly heritable for both target and non-target conditions and did not demonstrate the anterior/posterior patterning obtained for visual N1 amplitude. This study represents the first systematic assessment of heritability of these potential neurophysiological markers in families with a history of alcoholism and suggests that many of these ERP phenotypes have heritabilities strong enough to justify genomic screening for loci jointly influencing ERP abnormalities and liability to alcoholism. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:383–390, 1999. © 1999 Wiley-Liss, Inc.     

Event-related potentials to tones in the absence and presence of sleep spindles

The present study focused on event-related potentials to tones in the presence and absence of sleep spindles. Six undergraduates were studied throughout an experimental night, following an adaptation session. The event-related potentials to tone stimuli were averaged for each subject. Separate averages were determined for trials on which no sleep spindle occurred 2 s before or after a tone and trials in which spindle activity was present. Both voltage distribution maps and multivariate analysis of the waveforms produced significant differences between these conditions, which could be seen as a higher initial positive component and sustained positivity over the averaged epoch in the presence of spindles. Spectral analysis indicated that this result could not solely be ascribed to residual sigma activity in the spindle-present average. The results may provide insights into the functional role of sleep spindles in humans in addition to that suggested by a neurophysiological model of inhibition.     

Changes in direct current potentials during sleep deprivation

Previous research reported changes in steady-state brain electrical activity during sleep. However, due to the quasi-linear nature of the Direct Current (DC) changes, artifact contamination was a potential confound. The present study was performed to further explore DC potentials and to help establish its validity. Twenty-five male university students (13 control and 12 sleep-deprived; mean age 19 y (range 17–27 y) served as subjects. During wakefulness, subjects were tested every hour while standard EEG activity recordings were made, as well as DC measurement. Split plot analyses of variance (ANOVAs) revealed that changes in DC activity levels differed between the two groups. The control subjects showed the same pattern of decreasing DC observed previously with a return to baseline levels during waking hours. The sleep-deprived subjects showed a smaller decrease in DC level through the night, followed by a rise in DC level that continued until the end of the 24 h study. It was concluded that DC measurement reflects changes in brain state associated with fatigue that are not attributable to artifactual processes.     

Visual event-related brain potentials in 4-month-old infants at risk for neurodevelopmental impairments

The recording of event-related potentials (ERPs) is an electrophysiologic technique that has been used to evaluate the functional maturation of neural pathways responsible for recognition memory systems in infants and children. The purpose of this study was to evaluate ERP correlates of visual recognition memory in 4-month-old infants at risk for later cognitive impairments. We compared ERPs using a test of shape recognition at 4 months of age (adjusted for prematurity) in 16 high-risk, neonatal intensive care unit (NICU) survivors and 16 healthy full-term infants. ERPs were recorded while infants were familiarized with one stimulus (a red cross, 15 trials), then tested with 60 trials of this familiar stimulus and a novel stimulus (a red corkscrew). Both the NICU and control groups' ERPs demonstrated evidence of differential processing of the two stimuli, but the NICU groups' ERP patterns were distinctly different from those of the control group. In the NICU group, the novel stimulus elicited parietal positivity at 1000–1700 ms poststimulus, whereas in the control group the novel stimulus elicited occipital and frontal negativity at 500–1700 ms poststimulus. The ERP pattern demonstrated by the NICU group was atypical as it has not been previously described in healthy infants. The results of the study indicate that the ERP technique can be used to demonstrate altered patterns of neural activity during tasks of visual recognition memory in high-risk infants. We speculate that the atypical ERP patterns described in this study may indicate that patterns of synaptic organization were altered by neonatal events. © 1997 John Wiley & Sons, Inc. Dev Psychobiol 30 : 11–28, 1997     

Auditory event-related potentials reflect dedicated change detection activity for higher-order acoustic transitions

The processing of auditory changes at cortical level relies partly on dedicated change-detectors whose activity is reflected in the elicitation of the N1 and P2 event-related potentials (ERPs). In previous studies, N1 and P2 have been found only for first-order frequency transitions (i.e. constant-to-glide) but not for higher-order transitions (i.e. glide-to-constant). We tested whether this asymmetry is due to the complete lack, or the smaller number of dedicated higher-order change detectors compared to first-order change detectors by recording ERPs to constant-to-glide and glide-to-constant frequency transitions within pure and complex tones. For constant-to-glide transitions ERP amplitudes increased with the rate of frequency change and spectral complexity. Importantly, for glide-to-constant transitions, N1 was elicited, even though only for spectrally rich tones when the frequency-change rate was fastest. Thus, the asymmetry in auditory change-related N1 elicitation is attributable not to the lack of higher-order change detectors, but to their relatively low number.     

Event-related potentials during forced awakening: a tool for the study of acute sleep inertia

Sleep propensity and sleep inertia were assessed in 43 patients with excessive daytime sleepiness (EDS) and 21 sleep-deprived controls, using a forced awakening test under continuous electroencephalographic (EEG) recording. Event-related potentials (ERPs) were first obtained in waking, while participants performed a target detection auditory task. Subjects were then allowed to take a nap with lights off and sleep latency was calculated. After 3 min of continuous sleep, frequent and rare tones were suddenly presented again (and ERPs recorded) in a forced awakening condition, which was repeated a second time if patients fell asleep. ERPs in pre-nap wakefulness did not differ in patients and controls. On forced awakening, almost half (48%) of EDS patients retained morphologically normal ERPs, but showed a significant delay of P300 relative to waking. In the other half of the patients (and none of the controls), the N200/P300 complex to targets was replaced on forced awakening by high-amplitude negative waves ('sleep negativities'). Single subject analysis showed that 65% of patients had abnormal responses during forced awakening (significant P3 delay or sleep negativities), while only three of them (7%) had abnormal ERPs on wakefulness. The presence of sleep negativities was associated with shorter sleep latencies and increased target detection errors on forced awakening. Sleep negativities were more prevalent in narcolepsy and idiopathic hypersomnia than in EDS associated to psychiatric disorders. By combining sleep latency and ERP measures, the forced awakening test provided a robust and relatively rapid tool (45-60 min) to evaluate both sleep propensity and sleep inertia within a single recording session. The test allows each subject to act as his/her own control, thus increasing sensitivity. In the present series, it proved to be much more discriminative than waking ERPs alone to demonstrate specific abnormalities in patients complaining of excessive daytime sleepiness.     

大学生情绪标签与性别标签加工时程差异的事件相关电位研究

目的:比较大学生情绪标签与性别标签的加工差异,探讨情绪标签的时程.方法:选取17名在校大学生,进行情绪标签任务和性别标签任务,分别记录选择正确的情绪标签词和性别标签词的正确率与反应时.同时收集脑电数据进行事件相关电位参数分析,包括P1、早期负后波(EPN)和晚正波(LPP)三个脑电成分.其中,LPP由于时间窗口跨度宽,以50ms为间隔,分为7段(450～500 ms、500～550ms、550～600 ms、600～650ms、650 ～ 700 ms、700～750ms、750～ 800 ms).结果:情绪标签反应时长于性别标签[(1095.6±218.1)msvs.(1007.6±219.3) ms,P＜0.01],但两者的正确率差异无统计学意义[(92.1±5.8)％vs.(91.5±4.6)％,P＞0.05].情绪标签仅在550～600 ms的时间窗口内,LPP波幅大于性别标签[(5.9±3.2)μv vs.(4.8±2.8) μ.v,P＜0.05].其他脑电成分及其他时间窗口内的LPP,情绪标签与性别标签的波幅差异均无统计学意义(均P＞0.05).结论:本研究提示,与性别标签相比,情绪标签可能在某一时间段内存在情绪的符号加工过程,从而导致LPP波幅先上升,而标签情绪之后,又使LPP波幅下降,形成内在的情绪调节过程.     

Event-related potentials in an auditory semantic oddball task in humans

Whenever rare target stimuli are presented interspersed by frequent irrelevant stimuli (standards), the targets elicit a late parieto-central positive wave called P3. Usually standards and targets differ by a simple physical feature (e.g. tone pitch). Less consistent are the data obtained in semantic tasks, in which standards and targets are represented by different word classes. Given an equal number of words in the target and standard categories, each individual standard is more frequent than each target, that is, the frequency of the category is confounded with that of individual stimuli. In the present study participants were presented five semantic classes each being represented by 15 words. Words belonging to one particular class should be counted. Thus targets were rare (20%), although the frequencies of each word and of each semantic class were equal. A highly significant P3 was recorded. Its latency was longer, and the amplitude was smaller, than when standards and targets were two tones. These data indicate that brain waves recorded in semantic tasks are not necessarily manifestations of specific semantic processing.     

Age- and performance-related differences in source memory retrieval during early childhood: Insights from event-related potentials

Across early childhood, children's ability to remember individual items and the details that accompany these items (i.e., episodic memory) improves greatly. Given that these behavioral improvements coincide with increases in age, effects of age and performance are often confounded. This study used event-related potentials (ERPs) to investigate age- and performance-related differences in the neural processes underlying the development of memory for details during early childhood. Using a source memory paradigm, ERP components related to episodic memory, the negative component (Nc), and late slow wave (LSW) were examined in 4- to 8-year-old children. Analyses focused on trials for which children correctly remembered the source related to an item versus trials where the item was remembered but the source was forgotten. Results revealed LSW, but not Nc, differed as a function of age and performance. Specifically, LSW effects were similar across source correct and source incorrect trials in all high-performing children and in low-performing older children; however, LSW effects differed across conditions in low-performing younger children. Results show developmental differences in retrieval processes across early childhood and highlight the importance of considering age and performance when examining electrophysiological correlates of episodic memory during development.     

Effects of aging on event-related brain potentials and reaction times in an auditory oddball task

Auditory event-related potentials (ERPs) were recorded from 71 healthy individuals between 18 and 82 years of age during performance of a disjunctive reaction time task in an auditory oddball paradigm. The effects of aging on reaction times and on the latencies, amplitudes, and distributions of each of the main ERP components were examined. No significant slowing of the reaction times of the elderly subjects was observed in relation to the younger ones. The peak latencies of both the N1 and P2 components elicited by standard tones were slightly but significantly slowed with age. In the ERPs of target tones, the later, endogenous components (N2, P3, and SW) showed linear increases in latency as a function of age; the later the component, the longer the age-related delay. In general, aging was associated with less negativity (both N2 and SW) and more positivity (P3) over the anterior scalp, together with a smaller P3 and a more pronounced N2 over posterior scalp areas. Most of the effects observed in target ERPs were also evident in the difference waves derived from subtraction of the standard from the target ERPs, although the slope of the age-related latency increase of N2 was shallower and that of the P3 was steeper in the difference ERPs. These findings are discussed in relation to previous accounts of ERP changes with aging.