Source Dipole Analysis of the Early Components of the RREP

Occlusion of the inspiratory airway produces a series of early RREP components. The predominant early positive and negative peaks are seen over the parietal and frontal scalp respectively and have been hypothesised to represent parallel activation of somatosensory and motor cortices in a manner similar to electrically produced SEP components. An alternative hypothesis is that both components are produced by somatosensory cortex, with the frontally maximal negativity reflecting the activity of a tangential dipole source. Respiratory-related evoked potentials (RREPs) elicited by brief occlusion of the inspiratory airway, were recorded using 29 scalp electrodes from six subjects. Early latency components were analysed using the Electromagnetic Source Estimation (EMSE) program for modelling equivalent electrical dipoles, in order to suggest likely generator sources. Two hypotheses were tested: first, that radial dipoles generated by both pre- (motor cortex) and post-centrally (somatosensory cortex) produce the early components; and second, that generator sources are limited to the somatosensory cortex, with activity recorded as frontally maximal reflecting volume conduction from tangential dipoles. Results were highly consistent between subjects and suggested that Nf-P1 was best accounted for by two post-central and two pre-central radial dipoles supporting the first hypothesis. Locations of generator sources are discussed in relation to anatomical correlates.     

Electrophysiological evidence of sustained spatial attention effects over anterior cortex: Possible contribution of the anterior insula

Spatial attention can improve performance in terms of speed and accuracy; this advantage may be mediated by brain processes at both poststimulus (reactive) and prestimulus (proactive) stages. Here, we studied how visuospatial attention affects both proactive and reactive brain functions using event‐related potentials (ERPs). At reactive stage, effects of attention on parietal‐occipital components are well documented; little data are available on anterior components. Seventeen participants performed simple and discriminative response tasks, while voluntarily and steadily attending either the left or right visual hemifield throughout one block. Response speed was faster for the attended side. At ERP level, attending to one hemifield did not produce lateralization of proactive components—that is, the BP and the pN. As for poststimulus components, we confirmed the well‐known amplitude effects on the P1, N1, and P3. More interesting are results for the prefrontal components previously neglected in tasks modulating spatial attention. Previous studies suggest that these components reflect perceptual and sensory‐motor awareness (pN1 and pP1 components), and stimulus‐response mapping (pP2 component) associated to anterior insular activity. Spatial attention enhanced the pN1 and the pP1 amplitude but had no effect on the pP2. Overall, results extend knowledge on spatial attention, showing that sustained spatial attention affects the activity of anterior areas, such as the anterior insula, in addition to the known influence on occipital‐parietal areas. Top‐down spatial attention is likely mediated by increased sensory and sensory‐motor awareness for attended events; this effect is evident in reactive, not proactive, brain activity.     

Developmental aspects of automatic word processing: language lateralization of early ERP components in children, young adults and middle-aged subjects

Reading words elicits a very early evoked potential termed "recognition potential" with a latency of about 150 ms and clearly located in left posterior regions. A review of the current literature indicates that N150 marks the automatic lexical classification of a word, is relatively independent of the task, and is followed by a later negative and more anterior component which is sensitive to the task. However, from the literature it is not clear whether the left lateralization of the neural networks involved in word recognition changes with age and experience, and how this lateralization is related with behavioral performance. To this aim, based on a previously validated paradigm [Spironelli, C., Angrilli, A., 2006. Language lateralization in Phonological, Semantic and Orthographic tasks: a slow evoked potential study. Behavioral Brain Research 175, 296-304; Spironelli, C., Angrilli, A., 2007. Influence of Phonological, Semantic and Orthographic tasks on the early linguistic components N150 and N350. International Journal of Psychophysiology 64, 190-198], we ran an experiment on three samples of subjects, 28 children (mean: 10 years), 22 young adults (23 years) and 20 middle-aged subjects (59 years). Subjects had to read the same sample of words in three blocked tasks, Orthographic, Phonological and Semantic, while EEG was recorded from 38 scalp locations. Analysis performed on N150 and four regions of interest/quadrants revealed typical significant left posterior negativity in young and aged subjects, but reversed lateralization and greater right negativity in children compared with the two adult groups. Analysis of the later N350 revealed a significant three-way group x laterality x task interaction, showing greater left negativity on the Phonological task only in the two adult groups, and a bilateral component in children. Results indicate that the functional lateralization of linguistic neural networks involved in automatic word recognition and in phonological processing is not yet developed in linguistically competent children aged 10 years, whereas the observed lateralization is relatively stable and not degraded in moderately aged subjects. Results are discussed in view of their implications for age-related linguistic pathologies.     

Event-related potentials suggest early interaction between syntax and semantics during on-line sentence comprehension

Event-related potentials (ERPs) were used to investigate interaction between syntactic parsing and semantic integration processes during a visual sentence comprehension task. The linguistic stimuli were Finnish five-word sentences containing morphosyntactic and/or semantic violations. Single morphosyntactic violations evoked left anterior negativity (LAN) and P600 components. Single semantic violations elicited a robust N400 effect over the left hemisphere. A later and weaker N400-like response was also observed in the right hemisphere, left-right hemispheric latency difference being 40 ms. Combined morphosyntactic and semantic violations elicited a P600 component and a negative ERP component within the latency range of the LAN and N400 components. Further analysis of these ERP effects provided evidence for early processual interaction between syntax and semantics during on-line sentence comprehension. The hemispheric distribution of the LAN and N400 components was taken to suggest lateralization of initial morphosyntactic parsing and semantic integration processes to the left hemisphere. In contrast, the later syntax-related P600 component was observed as being more pronounced over the posterior areas of the right hemisphere.     

Magnetoencephalographic recording of steadystate visual evoked cortical activity

Summary Steady-state visual evoked magnetic fields (SSVEFs) were recorded in response to a flickering light source using a 37-channel magnetometer. The SSVEF had a sinusoidal waveform having the same fundamental frequency as the driving stimulus, which was either 6.0 Hz, 11.9 Hz, or 15.2 Hz. SSVEF topographies at each frequency had a dipoloar form over the posterior head that could well-modelled by single equivalent current dipoles. The best-fit dipoles were localized in posterior occipital cortex for the SSVEFs to 6.0 and 11.9 Hz stimuli and in more anterior and ventromedial occipital cortex for the 15.2 Hz SSVEP.This work was supported by grants from the Deutsche Forschungsgemeinschaft, the U.S. Office of Naval Research (N00014-93-1-0942) and N.I.M.H. (MH-25594). The authors thank Lacey Kurelowech, Parti Quint, Joslyne Foley and Annette Sterr for their help in data recording and technical assistance. We also thank Matt Marlow for software assistance and Prof. Thomas Elbert for helpful comments on data analysis.     

Topography and source analysis of brain activity associated with selective spatial attention and memory search

Summary We investigated the topographical aspects of the ERP reflections of visual spatial attention and memory search. Spatial attention was found to enhance the amplitudes of the P1 and N1 deflections. The brain activity in the P1-N1 latency range could be modeled with a single moving equivalent dipole, or alternatively with two stationary dipoles in a spatio-temporal dipole model. The dipoles were located in mesial and lateral posterior brain regions. Similar dipole solutions were obtained for ERPs to attended and unattended stimuli. Increasing the memory search requirements of the task resulted in an increase of late negativity, which was topographically distinguishable from the P3 component.     

High frequency vibration induced gating of subcortical and cortical median nerve somatosensory evoked potentials: different effects on the cervical N13 and on the P13 and P14 far-field SEP components.

Subcortical and cortical somatosensory evoked potentials (SEP) to median nerve stimulation were recorded before, during and after high frequency (270 Hz) vibration of the fingers 1-3 in 8 healthy subjects. A marked decrease of the amplitude of all potentials was observed. The attenuation of the sensory nerve action potential (SNAP) of the median nerve and the attenuation of SEP components N9, N11 and N13 showed no differences, while the attenuation of the subcortical P14 component was significantly higher. This is in accordance with a generator of the cervical N13 in the interneurons beside the lemniscal pathway. The cortical N20 (post-rolandic) was significantly more decreased in amplitude than P14 while P22 (pre-rolandic) remained reduced in amplitude like P14. An increased latency of the far-field subcortical P14 was observed, while P13 recorded in the same montage remained unchanged in latency. These findings suggest different generators of these peaks. A generator of P14 above the nucleus cuneatus is confirmed. A presynaptic generator of P13 is suspected.     

Sources of attention-sensitive visual event-related potentials

Summary In a study of the neural processes that mediate visual attention in humans, 32-channel recordings of event-related potentials were obtained from 14 normal subjects while they performed a spatial attention task. The generator locations of the early C1, P1, and Nl components of the visual evoked response were estimated by means of topographic maps of voltage and current source density in conjunction with dipole modelling. The topography of the C1 component (ca. 85 ms post-stimulus) was consistent with a generator in striate cortex, and this component was unaffected by attention. In contrast, the P1 and Nl components (ca. 95 and 170ms) exhibited current density foci at scalp sites overlying lateral extrastriate cortex and were larger for attended stimuli than for unattended stimuli. The voltage topographies in the 75–175 ms latency range were modeled with a 5-dipole configuration consisting of a single striate dipole and left-right pairs of dipoles located in lateral extrastriate and inferior occipito-temporal areas. This model was found to account for the voltage topographies produced by both attended and unattended stimuli with low residual variance. These results support the proposal that visual-spatial attention modulates neural activity in extrastriate visual cortex but does not affect the initial evoked response in striate cortex.This study was supported by ONR Contract N00014-89-J-1806, by grants from NIMH (MH-25594), NINCDS (NS 17778), the Human Frontier Science Program, DGICYT (PM92-0128), and by a Fulbright scholarship to the first author.     

Combined effects of alcohol and caffeine on the late components of the event-related potential and on reaction time

The effects of .7 ml/kg alcohol and 200 mg caffeine on the P200, N200, P300 and N500 difference wave components of the event-related potential and on reaction time (RT) were examined in 16 females who performed both simple and choice RT tasks. Alcohol slowed the decision time (DT) component of reaction time, lengthened the latency of the P200 and P300 components, reduced N200 amplitude, increased P300 amplitude at parietal sites, and modified the effect of sagittal site on N500 difference wave peak amplitude. Caffeine shortened DT in the choice RT task, shortened N200 latency at right hemisphere sites, and shortened N200 latency in the choice RT task in combination with alcohol compared to when alcohol was administered alone. Caffeine also increased P300 amplitude in the choice RT task and reduced the integral of the N500 difference wave at most sites when combined with alcohol. It was concluded that whereas alcohol slows attention allocation and impairs working memory, caffeine accelerated response-related decisions and enhanced cortical arousal.     

P300 topography of amplitude/latency correlations

Summary The correlational association from 19 electrode sites between peak amplitude and latency for the P3(00) event-related brain potential (ERP) for n=80 homogeneous subjects was assessed using a simple auditory discrimination task. The correlation strength varied systematically across scalp topography in different ways for the various ERP components. For the target stimuli, P3 amplitude and latency were negatively correlated and most tightly coupled over the frontal-central and right medial/lateral recording sites. In contrast, the N1 produced negative correlations that were strongest over the left and right central/lateral locations; P2 demonstrated a positive correlation that was strongest frontally and centrally; N2 demonstrated a positive correlations that was strongest over the central and parietal sites. ERPs from the standard stimuli produced generally similar patterns for the P3 and P2 components, with only weak or no reliable effects observed for the N1 and N2 potentials. Taken together, the findings suggest that analysis of amplitude/latency correlational relationships can provide information about ERP component generation. Theoretical implications are discussed.Collaborative studies on the Genetics of Alcoholism (H. Begleiter, SUNY HSCB, Principal Investigator, T. Reich, Washington University, Co-Principal Investigator) includes six different centers where data collection takes place. The six sites and Principal Investigator and Co-Investigators are: Indiana University (J. Nurnberger, Jr., P.M. Conneally); University of Iowa (R. Crow, S. Kuperman); University of California, San Diego and The Scripps Research Institute (M. Schuckit, F.E. Bloom); University of Connecticut (V. Hesselbrock); State University of New York, Health Science Center at Brooklyn (H. Begleiter, B. Porjesz); Washington University in St. Louis (T. Reich, C.R. Cloninger). This national collaborative study is supported by the National Institute on Alcohol Abuse and Alcoholism (NIAAAA) by U.S.P.H.S. grant U10AA08402-07, This paper is publication number NP10292 from The Scripps Research Institute.     

性别因素对老年期神经系统变性过程的影响

目的：研究探讨正常人进入老年期后，性别和年龄对事件相关电位的交互作用影响是否仍然持续。方法：应用神经心理学测试和MRI检查筛选日本冲绳县年龄在60岁以上的正常老年人40名。其中男性17名，平均年龄是72．2±8．6岁；女性23名，平均年龄是75．7±8．2岁。应用听觉“oddball”范式诱发事件相关电位P300。分析Fz和Pz部位记录到的事件相关电位内源性成分P300和N2b。结果：P300潜伏期、P300波幅和N2b潜伏期的组间差异不显著。于Fz部位，男性组的N2b波幅低于女性组（F=4．59，P=0．039）。P300潜伏期和P300波幅与年龄的相关性，仅见于男性组（Fz-P300潜伏期：r=0．584，P=0．014；Fz-P300波幅：r=-0．782，P〈0．001；Pz—P300潜伏期：r=0．587，P=0．013；Pz—P300波幅：r=-0．657，P=0．004）。P300潜伏期和P300波幅对年龄的线性回归坡度，在两组闾均有显著性差异，在男性组更为陡峭（Fz—P300潜伏期：t=2．11，P=0．042；Fz-P300波幅：t=2．55，P=0．015；Pz-P300潜伏期：t：2．70，P=0．011：Pz-P300波幅：t=3．00，P=0．005）。结论：性别因素对老年期神经系统变性过程有显著影响。     

Hemispheric differences in auditory oddball responses during monaural versus binaural stimulation

Hemispheric lateralization of early event-related potentials (ERPs; e.g. N1) is largely based on anatomy of the afferent pathway; lateralization of later auditory ERPs (P2/N2, P250, P3b) is less clear. Using 257-channel EEG, the present study examined hemispheric laterality of auditory ERPs by comparing binaural and monaural versions of an auditory oddball task. N1 showed a contralateral bias over auditory cortex in both hemispheres as a function of ear of stimulation, although right hemisphere sources were activated regardless of which ear received input. Beginning around N1 and continuing through the time of P3b, right hemisphere temporal–parietal and frontal areas were more activated than their left hemisphere counterparts for stimulus evaluation/comparison and target detection. P250 and P3b component amplitudes, topographies, and source estimations were significantly influenced by ear of stimulation, with right hemisphere activity being stronger. This was particularly true for anterior temporal and inferior frontal sources which were more strongly associated with the later, more cognitive components (P250, P3b). Results are consistent with theories of a right hemisphere network that is prominently involved in sustained attention, stimulus evaluation, target detection, and working memory/context updating.     

Flow of activation from V1 to frontal cortex in humans

This study provides a time frame for the initial trajectory of activation flow along the dorsal and ventral visual processing streams and for the initial activation of prefrontal cortex in the human. We provide evidence that this widespread system of sensory, parietal, and prefrontal areas is activated in less than 30 ms, which is considerably shorter than typically assumed in the human event-related potential (ERP) literature and is consistent with recent intracranial data from macaques. We find a mean onset latency of activity over occipital cortex (C1(e)) at 56 ms, with dorsolateral frontal cortex subsequently active by just 80 ms. Given that activity in visual sensory areas typically continues for 100-400 ms prior to motor output, this rapid system-wide activation provides a time frame for the initiation of feedback processes onto sensory areas. There is clearly sufficient time for multiple iterations of interactive processing between sensory, parietal, and frontal areas during brief (e.g., 200 ms) periods of information processing preceding motor output. High-density electrical mapping also suggested activation in dorsal stream areas preceding ventral stream areas. Our data suggest that multiple visual generators are active in the latency range of the traditional C1 component of the ERP, which has often been taken to represent V1 activity alone. Based on the temporal pattern of activation shown in primate recordings and the evidence from these human recordings, we propose that only the initial portion of the C1 component (approximately the first 10-15 ms; C1(e)) is likely to represent a response that is predominated by V1 activity. These data strongly suggest that activity represented in the "early" ERP components such as P1 and N1 (and possibly even C1) is likely to reflect relatively late processing, after the initial volley of sensory afference through the visual system and involving top-down influences from parietal and frontal regions.     

Aging effects on selective attention-related electroencephalographic patterns during face encoding

Previous electrophysiological studies revealed that human faces elicit an early visual event-related potential (ERP) within the occipito–temporal cortex, the N170 component. Although face perception has been proposed to rely on automatic processing, the impact of selective attention on N170 remains controversial both in young and elderly individuals. Using early visual ERP and alpha power analysis, we assessed the influence of aging on selective attention to faces during delayed-recognition tasks for face and letter stimuli, examining 36 elderly and 20 young adults with preserved cognition. Face recognition performance worsened with age. Aging induced a latency delay of the N1 component for faces and letters, as well as of the face N170 component. Contrasting with letters, ignored faces elicited larger N1 and N170 components than attended faces in both age groups. This counterintuitive attention effect on face processing persisted when scenes replaced letters. In contrast with young, elderly subjects failed to suppress irrelevant letters when attending faces. Whereas attended stimuli induced a parietal alpha band desynchronization within 300–1000 ms post-stimulus with bilateral-to-right distribution for faces and left lateralization for letters, ignored and passively viewed stimuli elicited a central alpha synchronization larger on the right hemisphere. Aging delayed the latency of this alpha synchronization for both face and letter stimuli, and reduced its amplitude for ignored letters. These results suggest that due to their social relevance, human faces may cause paradoxical attention effects on early visual ERP components, but they still undergo classical top–down control as a function of endogenous selective attention. Aging does not affect the face bottom–up alerting mechanism but reduces the top–down suppression of distracting letters, possibly impinging upon face recognition, and more generally delays the top–down suppression of task-irrelevant information.     

Sequence-sensitive subcomponents of P300: Topographical analyses and dipole source localization

P300 amplitude and reaction time (RT) are strongly affected by the sequence of events preceding the eliciting stimulus. Sommer, Leuthold and Soetens (1999) found that robust sequential effects in P300 amplitude could be dissociated from more variable sequential effects in RTs. However, global changes in P300 amplitude and topography gave rise to the suggestion that sequential effects are specific for a subcomponent of P300 that is separate from and anterior to the classical parietal P300. Here, confirming evidence for dissociable subcomponents of P300 is reported from two experiments. Independent component analysis separated a centrally distributed sequence-sensitive subcomponent from a more parietal subcomponent. Subsequent dipole source analysis indicated a deep mesial source for the sequence-sensitive subcomponent. Overlap with reafferent somatosensory activity appears to be responsible for an apparent lateralization of this component towards the hemisphere ipsilateral to the responding hand.     

Changes in Evoked Potentials on Increases in the Difficulty of Visual Searches in Humans

Monopolar evoked potentials (EP) in the frontal, parietal, temporal, and occipital leads in 16 young healthy subjects were analyzed during visual searches of increasing difficulty. Increases in the complexity of the visual search and addition of “noise” to visual stimuli added significant difficulty to the image recognition task, which was reflected in increases in search times and errors. Correlation of changes in EP and search parameters was seen mainly in the frontal leads: there were significant positive relationships between the N2 and P4 components and the SN–SP difference wave on the one hand and search difficulty on the other; there was a negative relationship with the P3 component, probably due to an increase in the duration and amplitude of the preceding N2 component. The N2 and P4 components were most marked in the frontal leads. We suggest that these data provide evidence of increasing dominance of frontal structures in the attention control system as the visual task increases in difficulty.     

Event-related potential correlates of perceptual and functional categories: comparison between stimuli matching by identity and equivalence

Event-related potentials (ERPs) correlates of two test criteria of an abstract category task were dissociated. In a stimulus equivalence task, 10 subjects observed pairs of figures presented serially in three conditions: reflexivity (generalized identity), equivalence (arbitrary derived relations from a previous training), and unrelated pairs. They were instructed to decide whether the second item in a pair matched or mismatched the first one. Participants' performance in reflexivity matching tests was faster and more accurate than in equivalence matching or mismatching responses. In the three conditions, an occipital P2, a frontal N2 and a parietal P3 ERP component were elicited. The earlier components P2 and N2 exhibited reflexivity matching effects, while the later component (P3) exhibited the only equivalence matching effect. In addition, the subtracted ERP components from unrelated minus identity and unrelated minus equivalence trials were computed within two time windows: 150-250ms (dN300) and 350-450ms (dN400). While both dN300 waves were not significantly different, the comparison of both dN400 waves showed statistical differences. Correlates of partially perceptual (but contextually abstract) concepts are elicited earlier than those of pure abstract concepts. These ERPs correlates of stimulus equivalence relation tests of semantic categories are in concordance with the behavioral data.     

Does electroconvulsive therapy (ECT) affect cognitive components of auditory evoked P300?

Electroconvulsive therapy (ECT), as a treatment tool for psychiatric disorders, is believed to be safe and effective. Nevertheless, it has a negative impact on cognitive functioning, especially on memory, causing both retrograde and anterograde amnesia. However, ECT effects on more subtle stages of information processing are not studied enough. Event-related potentials, and especially P300, are thought to reflect physiology of cognition. Thus, we aimed to evaluate the effects of ECT treatment on parameters of endogenous components (N2, P3) of the P300 potential. Seventeen patients suffering from schizophrenia, schizoaffective disorder and recurrent depressive disorder participated at the study. After the course of ECT, significant increase of N2 amplitude in parietal midline region and prolongation of P3 latency in frontal midline region, of which the magnitude positively correlated with the number of ECT procedures, have been obtained.     

Paradoxical scalp lateralization of the P100 cognitive somatic potential in humans: a magnetic field study

In somatic selective attention, electrical brain mapping disclosed a P100 cognitive electrogenesis with a scalp field paradoxically lateralized ipsilaterally to the target finger stimulus. We used 64 sensors magnetoencephalography (MEG) and source localization software in six normal humans to identify the P100 neural generator. Calculated dipole sources for P100 were iteratively compared with the recorded MEG data. The equivalent dipole at somatic P100 latency was located in the parietal lobe contralateral to the finger stimulus and had an oblique positive gradient pointing towards the ipsilateral side, thus explaining the paradoxical positivity in electrical brain mapping. It is suggested that the somatic P100 is generated in parietal area 7b which indeed appears to be specialized for cognitive processing within the somatic modality rather than for multimodal association.     

Do Task and Sex Differences Influence the Visual Evoked Potential?

Visual evoked potentials were recorded from each hemisphere of both male and female subjects at a parietal and a central site while concurrent spatial or verbal mental tasks were performed. The data were analyzed by means of an automated procedure for peak identification and each component's latency and amplitude was submitted to analysis of variance. No convincing taskhemisphere interactions were found, although several components, particularly the later ones, showed either task or hemisphere related effects. At both sites, females showed greater amplitude of the N2 component for both hemispheres and both cognitive tasks. Sex differences also emerged on components P6 and N6 which were consistent with the idea that females show differential hemisphere involvement in spatial tasks.