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PubMed2007

Predicting coma and other low responsive patients outcome using event-related brain potentials: a meta-analysis.

OBJECTIVE: A meta-analysis was performed to estimate the predictive power (odd ratio, OR) for awakening of auditory event-related potential (ERP) components in low responsive patients with stroke or hemorrhage, trauma, anoxic, post-operative, and metabolic encephalopathy etiologies. METHODS: We reviewed MEDLINE and analyzed citations for retrieved articles. Logistic regressions were applied on patient samples (Glasgow Coma Scale <12) across and for separate etiologies. RESULTS: For stroke and hemorrhage the ORs with 95% confidence intervals were: 2.05 [1.12-3.75] (N100), 4.47 [1.92-10.44] (MMN), 10.29 [2.00-52.79] (P300), for trauma: 1.63 [0.70-3.80] (N100), 4.72 [1.35-16.44] (MMN), 12.89 [4.82-34.43] (P300), anoxic: 8.03 [2.83-22.75] (N100), 15.50 [4.27-56.26] (MMN), 5.93 [2.38-14.77] (P300), post-operative: 10.66 [1.98-57.50] (N100), metabolic encephalopathy: 2.12 [0.34-13.13] (N100), 3.60 [0.28-46.36] (MMN), 7.71 [0.75-79.77] (P300), and all etiologies: 2.85 [1.91-4.27] (N100), 6.53 [3.55-12.01] (MMN), and 8.79 [4.88-15.83] (P300). Based on six N100 studies (N=548 patients), five MMN studies (N=470), and six P300 studies (N=313), the N100, MMN, or P300, when present, significantly predicted awakening, P300 and MMN being significantly better predictors than N100. CONCLUSIONS: The MMN and P300 appear to be reliable predictors of awakening. SIGNIFICANCE: The prognostic assessment of low responsive patients with auditory ERP should take into account both MMN and P300.

Coma↗
PubMed2004

What is common to brain activity evoked by the perception of visual and auditory filled durations? A study with MEG and EEG co-recordings.

EEG and MEG scalp data were simultaneously recorded while human participants were performing a duration discrimination task in visual and auditory modality, separately. Short durations were used ranging from 500 to 900 ms, among which participants had to discriminate a previously memorized 700-ms "standard" duration. Behavioral results show accurate but variable performance within and between participants with expected modality effects: the percentage of responses was greater and the mean response time was shorter for auditory than for visual signals. Sustained electric and magnetic activities were obtained correlatively to duration estimation, but with distinct spatiotemporal properties. Electric CNV-like potentials showed fronto-central negativity in both modalities, whereas magnetic sustained fields were distributed with respect to the modality of the interval to be timed. Time courses of these slow brain activities were found to be dependent on stimulus duration but not on its modality nor on the recording signal (EEG or MEG). Source reconstruction demonstrated that these sustained potentials/fields were generated by superimposed contributions from visual and auditory cortices (sustained sensory responses, SSR) and from prefrontal and parietal regions. By using these two complementary techniques, we thus demonstrated the involvement of frontal and parietal cerebral cortex in human timing.

Acoustic Stimulation↗
PubMed2004

Changes in emotional tone and instrumental timbre are reflected by the mismatch negativity.

The present study examined whether or not the brain is capable to preattentively discriminate tones differing in emotional expression or instrumental timbre. In two event-related potential (ERP) experiments single tones (600 ms) were presented which had been rated as happy or sad in a pretest. In experiment 1, 12 non-musicians passively listened to tone series comprising a frequent (standard) single musical tone played by a violin in a certain pitch and with a certain emotional connotation (happy or sad). Among these standard tones deviant tones differing in emotional valence, either in instrumental timbre or in pitch were presented. All deviants generated mismatch negativity (MMN) responses. The MMN scalp topography was similar for all of the three deviants but latency was shorter for pitch deviants than for the other two conditions. The topography of the mismatch responses was indistinguishable. In a second experiment, subjects actively detected the deviant tones by button press. All detected deviants generated P3b waves at parietal leads. These results indicate that the brain is not only able to use simple physical differences such as pitch for rapid preattentive categorization but can also perform similar operations on the basis of more complex differences between tones of the same pitch such as instrumental timbre and the subtle timbral differences associated with different emotional expression. This rapid categorization may serve as a basis for the further fine-grained analysis of musical (and other) sounds with regard to their emotional content.

Acoustic Stimulation↗
PubMed2005

The nature of switch cost: task set configuration or carry-over effect?

The primary goal of the present study was to differentiate variants of each class of hypothetical models of task switching. Two event-related potentials, the lateralized readiness potential (LRP) and P300 were analyzed to infer the roles of advance reconfiguration and carry-over effect upon task switching. Participants performed two tasks in a random order, so that on each trial, they either repeated the task from the previous trial or switched to another task. Pre-cues that preceded each stimulus were either informative (task-cueing conditions), specifying which of the two tasks to perform, or uninformative (no task-cueing conditions). The results showed that the mean reaction time (RT) and the interval between stimulus onset and LRP onset were longer for switch than for repeat trials. This suggested that task switching affected processes before LRP onset (including stimulus identification and response selection). A further analysis of P300 confined task switching to the process after the stimulus identification stage. Task cueing, meanwhile, influenced both the latency and peak amplitude of P300, suggesting that the cueing effect occurred prior to the response selection stage. The model of configuration-execution with moderate modifications is a candidate to explain the present results.

Adolescent↗
PubMed2005

Source analysis of the N2 in a cued Go/NoGo task.

Previous source analyses of event-related potential (ERP) data elicited in Go/NoGo tasks have suggested that the anterior cingulate cortex (ACC) plays an important role in response inhibition. So far, however, source models were derived for the difference wave Go stimulus minus NoGo stimulus. This difference wave is confounded with motor- and attention-related activity. To avoid these confounds, we alternatively derived source models for NoGo stimuli only. The problem of the NoGo-N2 being superimposed on a positive deflection was addressed in two ways. First, a baseline correction was applied using the time points just preceding and succeeding the NoGo-N2. Second, a separate source model was derived at the maximum amplitude of this positive deflection. Subjects were presented with a cued version of the continuous performance task (CPT; ABX). In a second study, the probability of the Go stimulus was gradually increased to heighten subjects' tendency to respond and, as a consequence, to enhance the amplitude of the NoGo-N2. The source models of the NoGo-N2 consistently indicated bilateral dipole pairs in medial frontal regions. This is in accordance with a generator in the anterior cingulate cortex.

Adult↗
PubMed2005

Electrophysiological evidence implicates automatic low-level feature detectors in perceptual asymmetry.

Perceptual asymmetry has been demonstrated behaviorally using frequency modulated (FM) stimuli: a modulated tone is easier to detect among unmodulated distracters than the converse. We demonstrate perceptual asymmetry for FM tones in the mismatch negativity (MMN) component of the event-related potential, regardless of whether the participant attends to the tones. These results suggest that perceptual asymmetry reflects the automatic activation of low-level feature detectors in the auditory system.

Acoustic Stimulation↗
PubMed2005

Preattentive representation of feature conjunctions for concurrent spatially distributed auditory objects.

The role of attention in conjoining features of an object has been a topic of much debate. Studies using the mismatch negativity (MMN), an index of detecting acoustic deviance, suggested that the conjunctions of auditory features are preattentively represented in the brain. These studies, however, used sequentially presented sounds and thus are not directly comparable with visual studies of feature integration. Therefore, the current study presented an array of spatially distributed sounds to determine whether the auditory features of concurrent sounds are correctly conjoined without focal attention directed to the sounds. Two types of sounds differing from each other in timbre and pitch were repeatedly presented together while subjects were engaged in a visual n-back working-memory task and ignored the sounds. Occasional reversals of the frequent pitch-timbre combinations elicited MMNs of a very similar amplitude and latency irrespective of the task load. This result suggested preattentive integration of auditory features. However, performance in a subsequent target-search task with the same stimuli indicated the occurrence of illusory conjunctions. The discrepancy between the results obtained with and without focal attention suggests that illusory conjunctions may occur during voluntary access to the preattentively encoded object representations.

Acoustic Stimulation↗
PubMed2005

A neurophysiological study of the detrimental effects of alprazolam on human action monitoring.

In order to adapt their behavior to different unexpected situations, humans need to be able to monitor their performance and detect and correct errors. Benzodiazepines have long been shown to impair performance in humans, but the performance-related neurophysiological processes targeted by these drugs remain largely unknown. In the present article, we assessed the impact of alprazolam administration on relevant aspects of action monitoring, i.e., the monitoring of response conflict and the detection and correction of errors by means of neurophysiological measures. Multichannel event-related brain potentials (ERPs) were recorded to assess the impact of the benzodiazepine alprazolam (0.25 mg and 1.00 mg) on action monitoring and motor preparation in a group of twelve healthy male volunteers who participated in a double-blind cross-over placebo-controlled clinical trial involving a letter flanker task. Error detection was evaluated using the error-related negativity (ERN); response conflict on correct trials was measured by means of the N2 amplitude difference between congruent and incongruent trials; motor preparation was assessed by means of the lateralized readiness potentials (LRPs); and post-error adjustments were assessed by measuring post-error slowing in reaction time. Alprazolam significantly reduced the amplitude of the ERN and the number of corrective responses and increased reaction time and LRP latencies. The drug had no effect on amplitude differences in the N2 component between congruent and incongruent trials or on post-error slowing. Thus, alprazolam was shown to affect brain correlates of error detection (ERN) and motor preparation (LRPs), while it did not disturb conflict monitoring on correct trials (N2) or post-error adjustments of behavior.

Adult↗
PubMed2005

Horizontal and vertical Simon effect: different underlying mechanisms?

Reaction times are usually faster when stimulus and response occur at the same location than when they do not, even if stimulus location is irrelevant to the task (Simon effect). This effect was found with both horizontal and vertical stimulus-response arrangements. The same mechanisms have been proposed to be involved in either case. Here, we compared a horizontal and a vertical Simon task by means of a RT time-course analysis of the Simon effect. Also, we analysed the lateralised readiness potential (LRP), an index of covert response-preparation processes. In the horizontal task, the Simon effect decays over time and pre-activation occurs above the motor cortex ipsilateral to the stimulus. In contrast, the Simon effect does not decay over time and no early incorrect LRP deflection is observed in the vertical task. These findings suggest that typical activation accounts can fit only the horizontal Simon effect, while a translation explanation is more suitable for the vertical Simon effect.

Adult↗
PubMed2006

Volition and the idle cortex: beta oscillatory activity preceding planned and spontaneous movement.

Prior to the initiation of spontaneous movement, evoked potentials can be seen to precede awareness of the impending movement by several hundreds of milliseconds, meaning that this recorded neural activity is the result of unconscious processing. This study investigates the neural representations of impending movement with and without awareness. Specifically, the relationship between awareness and 'idling' cortical oscillations in the beta range (18-24Hz) was assessed. It was found that, in situations where there was awareness of the impending movement, pre-movement evoked potentials were associated with a decrease in beta range oscillations. In contrast, when awareness of the impending movement was not present, the onset of the pre-movement potential was associated with tonic levels of beta range oscillations. A model is considered where by distributed neural activity remains outside of conscious awareness through the persistence of tonic slow wave cortical oscillations.

Adult↗
PubMed2006

The effects of music exposure and own genre preference on conscious and unconscious cognitive processes: a pilot ERP study.

Did Beethoven and Mozart have more in common with each other than Clapton and Hendrix? The current research demonstrated the widely reported Mozart Effect as only partly significant. Event-related brain potentials (ERPs) were recorded from 16 professional classical and rock musicians during a standard 2 stimulus visual oddball task, while listening to classical and rock music. During the oddball task participants were required to discriminate between an infrequent target stimulus randomly embedded in a train of repetitive background or standard stimuli. Consistent with previous research, the P3 and N2 ERPs were elicited in response to the infrequent target stimuli. Own genre preference resulted in a reduction in amplitude of the P3 for classical musicians exposed to classical music and rock musicians exposed to rock music. Notably, at the pre-attentive stage of processing (N2) beneficial effects of exposure to classical music were observed for both groups of musicians. These data are discussed in terms of short and long-term music benefits on both conscious and unconscious cognitive processes.

Acoustic Stimulation↗
PubMed2005

Effects of pre-stimulus processing on subsequent events in a warned Go/NoGo paradigm: response preparation, execution and inhibition.

The cued Go/NoGo task elicits response preparation during the foreperiod, and, depending on the S2 signal, either response execution or inhibition. This study aimed to determine how processes in the foreperiod might affect or predict post-S2 processing. Thirty-two adults participated in a cued Go/NoGo task (50% Go), with a median split of mean RT producing "Fast" and "Slow" groups. ERP measures were subjected to both ANOVA and regression techniques. There were no differences in the NoGo N2 effect related to response speed, nor was the effect related to pre-S2 processes. The anterior shift of the NoGo P3 was larger in the Fast group, and while the late CNV was associated with the absolute amplitude of both Go and NoGo P3, it was not related to the anterior-posterior Go/NoGo differences. Together, these data suggest that the inhibitory process may be reflected in the NoGo P3 effect, rather than the NoGo N2 effect.

Adolescent↗
PubMed2005

Nicotinic modulation of human auditory sensory memory: Evidence from mismatch negativity potentials.

Impairment in mismatch negativity (MMN) generation is a robust biological marker of schizophrenia. Understanding the physiological and pharmacological processes involved in its generation may therefore advance our understanding of this complex disorder. The present study tested if acute administration of nicotine modulates human auditory sensory memory as measured with MMN. ERP responses to tone duration deviants were recorded using a stimulation protocol with continuously changing (roving) standard stimuli in order to measure the effect of stimulus repetitions on encoding of new stimuli (MMN memory trace effect). Twenty healthy adult volunteers were randomly assigned to receive either a nicotine gum or placebo after a baseline ERP recording. Nicotine administration augmented MMN amplitude in the treatment group compared to the baseline recording, while no MMN change was found in the placebo group. The drug effect was due to a selective enhancement of a frontal positive potential to standard stimuli (from 80-200 ms post-stimulus), while the negativity to deviants remained unaffected. Furthermore, under nicotine stimulation this repetition positivity showed a more marked increase with stimulus repetition compared to baseline and placebo. These results have potential implications for schizophrenia by suggesting that nicotinic agonists could ameliorate patients' MMN deficits by improving stimulus encoding and sensory memory trace formation.

Acoustic Stimulation↗
PubMed2006

The effect of task preparation in task switching as reflected on lateralized readiness potential.

The present study examined whether task preparation had an equivalent beneficial effect for both switch and repeat trials in the context of a task switching paradigm. A pair-wise task-switching paradigm was used where each trial was comprised of two tasks that were either the same (task repeat) or different (task switch). The effect of preparation was manipulated so that participants either performed pure repeat trials or pure switch trials in separate blocks (foreknowledge conditions) or performed both switch and repeat trials within the same block (non-foreknowledge conditions). In addition, the time interval between the response to the first task and the onset of the next task's stimulus (response-stimulus interval, RSI) was set at either 300 ms or 600 ms. Both stimulus-locked and response-locked lateralized readiness potentials were measured to examine at what stage in time that task preparation affects the task performance. The results showed that task preparation had the same amount of beneficial effect on the stage of response selection for both switch and repeat trials, regardless of whether the RSI was short or long.

Adult↗
PubMed2006

Error processing in major depressive disorder: evidence from event-related potentials.

In a previous study we showed that errors following errors activate a strategic (prefrontal) mechanism. In an error trial (trial n) following an erroneous previous trial (trial n - 1) healthy control subjects were found to have enlarged (more negative) amplitudes of the error related negativity (ERN)/error negativity (Ne), an electrophysiological correlate of response monitoring, in response to a negative feedback signal. Contrary to that, patients with major depressive disorder showed smaller (less negative) ERN/Ne amplitudes. It has been discussed controversially whether errors of choice (e.g., pressing an incorrect response button in an Eriksen flanker task) and errors of commission (e.g., pressing a button when one is not supposed to in a Go/Nogo task) are related to different ERN/Ne mechanisms. In the present study, we examined whether our previous result only holds for errors of choice in an Eriksen flankers task or extends to errors of commission in a Go/Nogo task, as well. Ten patients with DSM-IV major depressive disorder and 10 matched controls participated in a Go/Nogo task with performance feedback which signaled monetary reward. Patients with major depressive disorder again showed a less negative ERN/Ne amplitude in error trials following error trials. This result might reflect impaired response monitoring processes in major depressive disorder resulting from an impaired activation of a central reward pathway and/or a deficit in strategic reasoning.

Adult↗
PubMed2004

Suprasegmental speech cues are automatically processed by the human brain: a mismatch negativity study.

This study investigates the electrical brain activity correlates of the automatic detection of suprasegmental and local speech cues by using a passive oddball paradigm, in which the standard Hungarian word 'banán' ('banana' in English) was contrasted with two deviants: a voiceless phoneme deviant ('panán'), and a stress deviant, where the stress was on the second syllable, instead of the obligatory first one. As a result, we obtained the mismatch negativity component (MMN) of event-related brain potentials in each condition. The stress deviant elicited two MMNs: one as a response to the lack of stress as compared to the standard stimulus, and another to the additional stress. Our results support that the MMN is as valuable in investigating processing characteristics of suprasegmental features as in that of phonemic features. MMN data may provide further insight into pre-attentive processes contributing to spoken word recognition.

Acoustic Stimulation↗
PubMed2005

Transient gamma-band response is dissociated from sensory memory as reflected by MMN.

The auditory gamma-band transient oscillatory response has been considered to reflect early cognitive processing and attention triggering, as has been suggested of the mismatch negativity (MMN). We examined whether the auditory gamma-band response was related to sensory memory as reflected by MMN. During the electroencephalogram (EEG) recordings, approximately 2000 click sounds were presented to nine healthy adult subjects with constant SOA of 120 or 170 ms in an ignored condition. At a probability of 10%, a click sound was randomly omitted from the stimulus sequence. EEG epochs responding to omitted clicks and to click sounds were averaged for analysis, respectively, and then those were convoluted by Gabor wavelet for the gamma-band response calculation. The MMN to a deviant omission in a sequence of click sounds was elicited with SOA of 120 ms which was shorter than the duration of temporal window of integration, whereas no MMN was elicited with SOA of 170 ms. In contrast with the MMN, the transient gamma-band response clearly commenced after the stimuli but not after the omissions, regardless whether SOA was short or long. The findings indicate that the brain process underlying the transient gamma-band response should be dissociated from the sensory memory function.

Adult↗
PubMed2005

Human auditory event-related potentials predict duration judgments.

Internal clock models postulate a pulse accumulation process underlying timing activities, with more accumulated pulses resulting in longer perceived durations. We investigated whether this accumulation is reflected in the amplitude of event-related brain potentials (ERPs) elicited by auditory stimuli with durations of 400-600 ms. In a duration discrimination paradigm, we found more negative amplitudes to physically identical stimuli when they were judged as longer than the memorized standard duration (500 ms) as compared to being classified as shorter. This sustained negativity was already developing during the first 100 ms after stimulus onset. It could not be explained as a bias to respond with a particular hand (lateralized readiness potential), but rather reflects a processing difference between the tones to be judged as shorter or longer. Our results are in line with models of time processing which assume that higher numbers of accumulated pulses of a temporal processor result in an increase in perceived duration.

Acoustic Stimulation↗