Auditory event related potentials and source current density estimation in phonologic/auditory dyslexics.

OBJECTIVE: To determine the generality of auditory processing impairment in phonologic dyslexics by studying their auditory Event-Related Potentials (ERPs) and the spatio-temporal distribution of their brain activity to auditory linguistic and non-linguistic stimuli with temporal and spectral discriminating cues. METHODS: Fourteen adult phonologic dyslexics and 14 normal reading students, all with high academic achievements, were compared. ERP waveform analysis and current density source estimation (Low resolution Electromagnetic Tomographic Analysis-LORETA) were conducted on 21-channel records from subjects who passively listened or actively discriminated 4 types of auditory stimuli: linguistic and non-linguistic stimuli that differed in spectral or temporal characteristics. RESULTS: Significant differences were found for all ERP latencies (N1, P2, N2, P3) in response to all stimuli, with dyslexics presenting longer latencies compared to normal readers. Current density distributions and their time courses also differed significantly, regardless of stimulus type or attention allocation. Among normal readers, early activity (around N1) was characterized by a rapid change of maximum activity from right to left temporal lobe. Later activity (around P3) was characterized by a stable temporal activity with bilaterally synchronous peak activity. Among the dyslexics, the early N1 activity was stable with left hemisphere prominence, with no alternation between the hemispheres, while the later P3 activity peaked earlier in the right hemisphere than in the left. CONCLUSIONS: Dyslexics were different from controls in processing all auditory stimuli: verbal and non-verbal stimuli with temporal as well as with spectral discriminating cues. The differences mainly consisted of latency and time courses of current density distributions, beginning as early as N1 and extending to the late P3. SIGNIFICANCE: Differences in processing auditory stimuli by phonologic dyslexics are not restricted to linguistic (phonological) stimuli, supporting a general auditory processing impairment in phonologic dyslexia.     

Fronto‐temporal alterations within the first 200 ms during an attentional task distinguish major depression,non‐clinical participants with depressed mood and healthy controls: A potential biomarker?

Attentional impairment in depression is a cardinal feature of depression and has been proposed as a candidate endophenotype for major depressive disorder. Event-related potentials (ERPs) elicited by oddball signal detection tasks provide objective markers of selective stimulus processing, and are pertinent endophenotypic markers for depression. While previous studies have sought to determine objective markers for attentional impairment in depression, evidence is inconsistent and may involve heterogeneity in relatively small samples. Here, we brought together oddball ERP recording with source localization of neural correlates of selective attention in outpatients with major depressive disorder (MDD; n = 78) and participants with depressed mood (PDM; n = 127) relative to healthy controls (CTL; n = 116). The key finding was a dimensional exaggeration of the P200 (140-270 ms) to both target (signal) and non-target (noise) stimuli, most pronounced in MDD, followed by PDM, relative to CTL. This exaggeration was coupled with slower and more variable response times, suggesting that neural systems are attempting to compensate for a difficulty in discriminating signal from noise. P200 alterations were localised to limbic (hippocampal), temporal and ventral prefrontal regions, key components of the signal detection network. A subsequent reduction and delay in the P300 was also revealed for MDD indicating that the pronounced lack of discrimination in clinical depression may also lead to impaired stimulus evaluation. This P200 increase in depression could provide a potential mechanism for the attentional impairment frequently observed in depression and consequent alterations in the P300 may differentiate clinically significant depression.     

Sources of cortical rhythms in adults during physiological aging: a multicentric EEG study

This electroencephalographic (EEG) study tested whether cortical EEG rhythms (especially delta and alpha) show a progressive increasing or decreasing trend across physiological aging. To this aim, we analyzed the type of correlation (linear and nonlinear) between cortical EEG rhythms and age. Resting eyes-closed EEG data were recorded in 108 young (Nyoung; age range: 18-50 years, mean age 27.3+/-7.3 SD) and 107 elderly (Nold; age range: 51-85 years, mean age 67.3+/-9.2 SD) subjects. The EEG rhythms of interest were delta (2-4 Hz), theta (4-8 Hz), alpha 1 (8-10.5 Hz), alpha 2 (10.5-13 Hz), beta 1 (13-20 Hz), and beta 2 (20-30 Hz). EEG cortical sources were estimated by low-resolution brain electromagnetic tomography (LORETA). Statistical results showed that delta sources in the occipital area had significantly less magnitude in Nold compared to Nyoung subjects. Similarly, alpha 1 and alpha 2 sources in the parietal, occipital, temporal, and limbic areas had significantly less magnitude in Nold compared to Nyoung subjects. These nine EEG sources were given as input for evaluating the type (linear, exponential, logarithmic, and power) of correlation with age. When subjects were considered as a single group there was a significant linear correlation of age with the magnitude of delta sources in the occipital area and of alpha 1 sources in occipital and limbic areas. The same was true for alpha 2 sources in the parietal, occipital, temporal, and limbic areas. In general, the EEG sources showing significant linear correlation with age also supported a nonlinear correlation with age. These results suggest that the occipital delta and posterior cortical alpha rhythms decrease in magnitude during physiological aging with both linear and nonlinear trends. In conclusion, this new methodological approach holds promise for the prediction of dementia in mild cognitive impairment by regional source rather than surface EEG data and by both linear and nonlinear predictors.     

注意缺陷多动障碍与智商及事件相关电位的关系

目的：研究事件相关电位(ERP)与智商(IQ)及注意缺陷多动障碍(ADHD)之间的相互关系。方法：采用肌电图诱发电位仪记录靶刺激及非靶刺激结果，结合测试智商的方法。结果：ADHD组事件相关电位靶刺激计数正确率显著低于对照组儿童；P2，P3潜伏期显著延长；NlP2峰峰值显著低于对照组；两次记录P3波重复性显著低于对照组儿童；IQ(包括总智商(FIQ)、言语智商(VIQ)、操作智商(PIQ))均显著低于对照组儿童；相关分析结果显示P2，N2，P3潜伏期与FIQ，PIQ呈显著负相关；NlP2峰峰值与FIQ，VlQ呈显著正相关。Logistic回归分析显示靶刺激计数正确率及FIQ为ADHD的显著保护因素，岛潜伏期与FIQ存在显著的交互作用。结论：ADHD患儿排除干扰的能力及认知功能显著受损。交互作用结果则显示IQ与P3潜伏期对ADHD的影响互为拮抗。提示ADHD患儿的额前区功能不成熟。     

"Aha!" effects in a guessing riddle task: an event-related potential study

Insight problem solving has been the topic of much investigation. It is believed widely that insight critically contains the process of breaking one's mental set. Recent functional magnetic resonance imaging (fMRI) research on puzzle solving showed that insight was associated with activities in anterior cingulate cortex (ACC) and other areas (Luo and Niki [2003]: Hippocampus 13:274-281). We proposed ACC might mediate processes of breaking one's mental set, given its well-known role in cognitive conflict. In the present research, high-density event-related potentials (ERPs) were recorded to examine the electrophysiologic correlates of insight problem solving. One hundred twenty interesting Chinese riddles (half difficult and half easy) were adopted as materials. For each trial, subjects were either given an easy puzzle followed by a keyword that was consistent with the subject's initial thinking ("No-aha answer"), or a difficult puzzle followed by a keyword that was consistent with an unusual interpretation, so that it broke the subject's initial mental set ("Aha answer"). Results from 14 subjects showed that Aha answers elicited a more negative ERP deflection than did No-aha answers in the time window from 250-500 msec after onset of the answer. The ERP difference wave (Aha minus No-aha answer) showed the maximum amplitude over the central site (Cz) with a peak latency of 380 msec (N380). Voltage and current density maps of the difference wave showed strong activity and current density in the frontocentral region. Dipole analysis localized the generator of the N380 in the ACC. N380 therefore probably reflects an "Aha!" effect, and the ACC generator may be involved in the breaking of mental set.     

Orienting and maintenance of spatial attention in audition and vision: an event-related brain potential study

We examined the effects of orienting and maintenance of attention on performance and event-related brain potentials (ERPs) in audition and vision. Our subjects selectively attended to sounds or pictures in one location (Maintenance of attention) or alternated the focus of their auditory or visual attention between left and right locations (Orienting of attention) in order to detect and press a response button to infrequent targets among the attended stimuli. Reaction times were longer in the Auditory Orienting condition and hit rates were lower and false alarm rates higher in the Visual Orienting condition than in the corresponding Maintenance conditions. Comparison of ERPs to the attended and unattended stimuli in the Auditory and Visual Orienting and Maintenance conditions revealed attention-related modulations of ERPs. In each modality, ERPs to attended stimuli were negatively displaced in relation to unattended stimuli at 100-250 ms from stimulus onset. These negative differences (Nds) showed modality-specific distributions and they were larger over the hemisphere contralateral to the attended sounds and pictures than over the ipsilateral hemisphere. Moreover, the Nd was larger in the Auditory Orienting condition than in the Auditory Maintenance condition, while no such difference was observed in the visual modality. In addition to the Nd, attended visual stimuli elicited a late positive response (LPR) in both Orienting and Maintenance conditions. In contrast to our recent functional magnetic resonance imaging (fMRI) study employing the same experimental paradigm and indicating orienting-related activity in the frontal and parietal cortices, no ERP responses specifically related to orienting were found in either modality.     

The neural basis of analogical reasoning: an event-related potential study

The spatiotemporal analysis of brain activation during the execution of easy analogy (EA) and difficult analogy (DA) tasks was investigated using high-density event-related brain potentials (ERPs). Results showed that reasoning tasks (schema induction) elicited a more negative ERP deflection (N500-1000) than did the baseline task (BS) between 500 and 1000 ms. Dipole source analysis of difference waves (EA-BS and DA-BS) indicated that the negative components were both localized near the left thalamus, possibly associated with the retrieval of alphabetical information. Furthermore, DA elicited a more positive ERP component (P600-1000) than did EA in the same time window. Two generators of P600-1000 were located in the medial prefrontal cortex (BA10) and the left frontal cortex (BA6) which was possibly involved in integrating information in schema abstraction. In the stage of analogy mapping, a greater negativity (N400-600) in the reasoning tasks as compared to BS was found over fronto-central scalp regions. A generator of this effect was located in the left fusiform gyrus and was possibly related to associative memory and activation of schema. Then, a greater negativity in the reasoning tasks, in comparison to BS task, developed between 900-1200 ms (LNC1) and 2000-2500 ms (LNC2). Dipole source analysis (EA-BS) localized the generator of LNC1 in the left prefrontal cortex (BA 10) which was possibly related to mapping the schema to the target problem, and the generator of LNC2 in the left prefrontal cortex (BA 9) which was possibly related to deciding whether a conclusion correctly follows from the schema.     

Selective anterior cingulate cortex deficit during conflict solution in schizophrenia: an event-related potential study

BACKGROUND: Schizophrenia research has gained a new focus on identification and further characterization of neurocognitive deficits in the search for behavioural endophenotypes of this disorder. The objective of this study was to explore differential cortical processing during executive control in schizophrenia as assessed with the attention network test (ANT). METHODS: Sixteen schizophrenic patients and sixteen healthy controls matched for gender, age, education, and nicotine consumption were tested with the ANT while recording 29-channel-electroencephalogram (EEG). Visual event-related potentials (ERP) N200 and P300 were topographically analyzed and cortical mapping using low resolution brain electromagnetic tomography (LORETA) was applied to localize neuroelectric generators of ERP. RESULTS: Behaviourally, significant differences between schizophrenic patients and controls were found only for the conflict condition (p<0.05) and for conflict adjusted by mean reaction time (p<0.01). Examining ERP of control subjects, N200 failed to show robust flanker congruency effects. P300 amplitude was reduced at Pz (p<0.05) and P300 latency was increased at Cz (p<0.005) for the conflict condition. Schizophrenic patients differed significantly in P300 latency at Cz during late conflict processing (p<0.005). Source analysis revealed a deficit in anterior cingulate cortex (p<0.05). CONCLUSION: Our results are in line with previous reports about dysfunctional ACC activation in schizophrenia and argue in favour of a selective deficit of cortical conflict resolution. It is further proposed that dysfunctional ACC activation during executive processing may be a neurophysiologic endophenotype candidate of schizophrenia.     

Transient human cortical responses during the observation of simple finger movements: a high-resolution EEG study

High-resolution event-related potentials (ERPs) were used to model the hemispherical representation of the transient cortical responses relating to the observation of movement during execution (right or left aimless finger extension). Subjects were seated in front of the observed person and looked at both their own and the observer's hand to receive similar visual feedback during the two conditions. In a visual control condition, a diode light moved at the observed person's hand. A first potential accompanying the movement execution peaked at about +110 msec over the contralateral somatomotor areas. It was followed by a potential (P300) peaking at about +350 msec over the central midline. In contrast, the potentials accompanying the movement observation peaked later over parietal-occipital other than somatomotor areas (N200 peak, +200 msec; P300 peak, +400 msec). Notably, the N200 was maximum in left parietal area whereas the P300 was maximum in right parietal area regardless the side of the movement. They markedly differed by the potentials following the displacement of the diode light. These results suggest a rapid time evolution (approximately 200-400 msec) of the cortical responses characterizing the observation of aimless movements (as opposite to grasping or handling). The execution of these movements would mainly involve somatomotor cortical responses and would be scarcely founded on the visual feedback. In contrast, the observation of the same movements carried out by others would require dynamical responses of somatomotor and parietal-occipital areas (especially of the right hemisphere), possibly for a stringent visuospatial analysis of the motor event.     

The effects of stress and statistical cues on continuous speech segmentation: an event-related brain potential study

The study of the processes involved in speech segmentation has gained special relevance in recent years by trying to establish what type of information listeners use to segment the speech signal into words. An event-related brain potential experiment was conducted in order to understand how two of these cues (statistical and stress cues) interact. The experiment consisted of the presentation of artificial speech streams in which words were marked either by statistical cues alone, or by a combination of statistical and stress cues. As a baseline, comparison streams were also created with the same syllables but organized in random order. Results showed an N400 component that marks the on-line segmentation of speech into words, and an increased positivity (P2 component) for languages that include both types of cues. Possible implications of these results for the process of speech segmentation are discussed.     

事件相关电位N400神经发生源研究

目的事件相关电位(event-related potentials,ERPs)N400是与语境歧义处理相关的高级认知电位,研究应用于精神分裂症的认知功能障碍。有关N400神经发生源,国内外均少有研究报道。本研究应用“低分辩率电磁断层扫描术(low resolution electromagnetic tomography,LORETA)”技术研究 N400的神经发生源。方法ERPs应用汉词语词对(S1-S2)诱发。S1-S2的关系为:语义关联对、语义非关联对和汉词-人造词对。脑电信号应用17导电极记录。被试为18例正常健康者,男9,女9,平均年龄25．2±4．4岁。应用LORETA软件中内含的“统计学非参数地形图(statistical non-parametric mapping,SnPM)”程序分析被试处理不同类语词时所激活的脑功能区差异。结果与语义关联词对中S2诱发ERPs相比,语义非关联词对中S2诱发出潜伏期在300-500 ms左右的负向偏转成分N400。分别比较S2开始后300-350 ms、350-400 ms、400-450 ms和450-500 ms时间窗内两类刺激语词激活的脑功能区,发现具有显著性差异的脑功能区集中在左半球的颞上回、颞中回、岛回、梭状回、后扣带回和海马旁回等区域。结论事件相关电位N400的神经发生源位于优势半球的颞叶及扣带回-海马结构。     

Frontal attentional responses to food size are abnormal in obese subjects: An electroencephalographic study

ObjectiveAre obese subjects characterized by a reduction of attentional cortical responses to the enlargement of food or body images?MethodsElectroencephalographic data were recorded in 19 obese and 15 normal-weight adults during an “oddball” paradigm. The subjects were given frequent (70%) and rare (30%) stimuli depicting faces (FACE), food (FOOD), and landscapes (CONTROL), and clicked the mouse after the rare stimuli. These stimuli depicted the same frequent stimuli graphically dilated by 25% along the horizontal axis. Bioelectrical impedance indexed subjects’ body fat percentage. Cortical attentional responses were probed by the difference between positive event-related potentials peaking around 400–500 ms post-stimulus for the rare minus frequent stimuli (P300). Low resolution electromagnetic source tomography (LORETA) estimated P300 sources.ResultsIn the FOOD condition, the amplitude of medial prefrontal P300 sources (Brodmann area 9) was lower in the obese than normal-weight subjects, and there was a negative correlation between the body fat percentage and the amplitude of these sources in all subjects as a single group.ConclusionsThese results disclose that prefrontal attentional processes to food size are abnormal in obese subjects.SignificanceThe present study motivates future research evaluating the effects of cognitive rehabilitation in obese subjects.     

Resting state eyes-closed cortical rhythms in patients with locked-in-syndrome: An eeg study

Objective

Locked-in syndrome (LIS) is a state of complete paralysis, except for ocular movements, which results from ventral brainstem lesions. Patients typically are fully conscious. Here we tested the hypothesis that electroencephalographic (EEG) rhythms are abnormal in LIS patients, possibly due to an impaired neural synchronization between brainstem and cerebral cortex.

Methods

Resting state eyes-closed EEG data were recorded in 13 LIS subjects and 15 cognitively normal control subjects. With reference to the individual alpha frequency (IAF), the bands of interest were delta (IAF-8 to IAF-6 Hz), theta (IAF-6 to IAF-4 Hz), alpha 1 (IAF-4 to IAF-2 Hz), alpha 2 (IAF-2 to IAF Hz), and alpha 3 (IAF to IAF + 2 Hz). Furthermore, beta 1 (13–20 Hz) and beta 2 (20–30 Hz) bands were also considered. Cortical EEG sources were estimated by low-resolution electromagnetic tomography (LORETA).

Results

The power of alpha 2 and alpha 3 sources in all regions was lower in patients with LIS compared to controls. The power of delta sources in central, parietal, occipital and temporal regions was higher in patients with LIS compared to controls.

Conclusions

These results suggest that cortical sources of resting state eyes-closed alpha and delta rhythms are abnormal in LIS patients.

Significance

LIS is accompanied by a functional impairment of cortical neuronal synchronization mechanisms in the resting state condition.     

Levels of error processing in Huntington's disease: a combined study using event-related potentials and voxel-based morphometry

Huntington's Disease (HD) is a neurogenetic disorder accompanied by an atrophy of the striatum and hence of the dopaminergic (DA) system. Neural processes subserving error processing presumably depend on the DA system. We assessed error processing in manifest HD and in presymptomatic HD-gene-mutation-carriers (pHD) with event-related potentials reflecting error processing (the error negativity or error-related negativity and the error positivity derived from a flanker-task. We found a reduction of the Ne in the case of HD compared to pHD reflecting dopamine system pathology. Despite the Ne being reduced in HD, behavioral adaptation was possible. In addition, the error-rates did not differ between the groups. Optimized voxel-based morphometry revealed that grey matter volume in the medial frontal gyrus is correlated with the Ne amplitude in symptomatic patients. In addition, the effect of a Ne-reduction was related to the grey matter underneath the medial frontal gyrus, which is in line with two theories of the Ne. In contrast, the Pe did not differ between the groups, suggesting that the Pe is decoupled from the DA system. Interestingly we found a reduction of a late slow negativity on correct responses, which possibly reflects decreased preparatory processes in HD compared to pHD as induced by the DA alterations in HD. In conclusion a deterioration in error processing in HD compared to pHD is mainly reflected by the Ne. The deterioration might rely on two factors: a neurofunctional and a neuroanatomical.     

The cerebral correlates of subliminal emotions: an electroencephalographic study with emotional hybrid faces

In a high‐resolution electroencephalographic study, participants evaluated the friendliness level of upright and inverted ‘hybrid faces’, i.e. facial photos containing a subliminal emotional core in the low spatial frequencies (< 6 cycles/image), superimposed on a neutral expression in the rest of the spatial frequencies. Upright happy and angry faces were judged as more friendly or less friendly than neutral faces, respectively. We observed the time course of cerebral correlates of these stimuli with event‐related potentials (ERPs), confirming that hybrid faces elicited the posterior emotion‐related and face‐related components (P1, N170 and P2), previously shown to be engaged by non‐subliminal emotional stimuli. In addition, these components were stronger in the right hemisphere and were both enhanced and delayed by face inversion. A frontal positivity (210–300 ms) was stronger for emotional than for neutral faces, and for upright than for inverted faces. Hence, hybrid faces represent an original approach in the study of subliminal emotions, which appears promising for investigating their electrophysiological correlates.     

Intersubject variability of functional areas in the human visual cortex

Intersubject variability of striate and extrastriate areas was mapped by conjoined use of positron emission tomography (PET) and magnetic resonance imaging (MRI). We used two dynamic bowtie-shaped random-dot patterns centered symmetrically around the vertical- and horizontal-meridian, respectively, presented during sequential PET scans in 11 subjects. Control condition was simple fixation on a central dot in absence of a surrounding random dot pattern. V1, V2, VP, V3, V3a, V4, V5, and “wordform” areas were identified. After spatial normalization to Talairach atlas space, mean locations and standard deviations about these mean locations for x-, y-, and z-axes were calculated for each area in both hemispheres and compared for differences. The mean standard deviation for all axes across all areas tested was found to be small (4.9 mm). No significant differences were found in the mean standard deviations for the x-, y-, and z-axes in the left hemisphere vs. their counterparts in the right hemisphere. However, when mean standard deviations in both hemispheres were polled together by axis, the mean standard deviation for the y-axis (5.3 mm) was found to be significantly different from the mean standard deviation for the x-axis (4.3 mm). Furthermore, in the left hemisphere, the mean standard deviation for the z-axis (5.7 mm) was significantly greater than the mean standard deviation for the x-axis (3.9 mm). The values reported in this study for mean location and standard deviation of visual areas can be used to establish confidence intervals for distinguishing normal variations from pathology and consequent brain reorganization. Hum. Brain Mapping 6:301–315, 1998. © 1998 Wiley-Liss, Inc.     

The role of Broca's area in regular past-tense morphology: an event-related potential study

It has been suggested that damage to anterior regions of the left hemisphere results in a dissociation in the perception and lexical activation of past-tense forms. Specifically, in a lexical-decision task in which past-tense primes immediately precede present-tense targets, such patients demonstrate significant priming for irregular verbs (spoke-speak), but, unlike control participants, fail to do so for regular verbs (looked-look). Here, this behavioral dissociation was first confirmed in a group of eleven patients with damage to the pars opercularis (BA 44) and pars triangularis (BA 45) of the left inferior frontal gyrus (i.e., Broca's area). Two conditions containing word-onset orthographic-phonological overlap (bead-bee, barge-bar) demonstrated that the disrupted regular-verb priming was accompanied by, and covaried with, disrupted ortho-phonological priming, regardless of whether prime stimuli contained the regular inflectional rhyme pattern. Further, the dissociation between impaired regular-verb and preserved irregular-verb priming was shown to be continuous rather than categorical; priming for weak-irregular verbs (spent-spend) was intermediate in size between that of regular verbs and strong verbs. Such continuous dissociations grounded in ortho-phonological relationships between present- and past-tense forms are predicted by single-system, connectionist approaches to inflectional morphology and not predicted by current dual-system, rule-based models. Event-related potential data demonstrated that N400 priming effects were intact for both regular and irregular verbs, suggesting that the absence of significant regular-verb priming in the response time data did not result from a disruption of lexical access, and may have stemmed instead from post-lexical events such as covert articulation, segmentation strategies, and/or cognitive control.