[Experimental modification of the terminal phase of the CNV].
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Adult↗
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[The influence of interference on the post-imperative phase of the CNV].
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Brain↗
[Electrophysiologic definition of sensory integration in the aphasic, (Evoked potentials, Slow potentials)].
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Aphasia↗
[Slow potentials related to events].
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Age Factors↗
[Comparative study of the CNV and the quantitative EEG during a simple motor task (author's transl)].
The purpose of this study was to evaluate CNV amplitude variability and its degree of covariance with the spontaneous EEG (quantified by FFT algorithm) and the reaction time. 14 healthy male subjects made from atypical for one hour, and they had to keep their eyes closed. Recordings were during this period. CNV experimental paradigm was performed (S1--S2 = 1500 msec). The major findings of this study were that: 1) the CNV amplitude progressively decreased during the first part of the test (habituation) and then tended to stabilize. While not correlated with the vigilance index of spontaneous EEG (alpha/theta + delta index) the CNV amplitude was significantly related to the alpha reactivity index (% alpha of spontaneous EEG--% alpha of the S1--S2 EEG), 2) the CNV slope (calculated by drawing two points situated at 600 msec and 1400 msec after S1) showed significant relationship to both these EEG indices and the reaction time. These data are discussed in terms of Cooper's distinction between "scopeutic" and "categoric" processes (1978) and in terms of the Tecce model of the CNV (1972).
Adult↗
[Emotional and attentive interferences and slow cerebral potentials (CNV-P 300) (author's transl)].
A study was conducted to establish possible correlations between electrophysiological indices and performance under neutral situations and those involving completing a double task of increasing complexity, by studying CNV and P 300 in young healthy men. The results demonstrated that: 1. After habituation, the CNV amplitudes were not related to performance. A significant correlation was noted only during the most complex tasks. 2. The CNV appears to depend mainly on endogenous factors, that is to say the aptitude and readiness of an individual to treat the information, rather than on the performance resulting from this treatment. 3. The amplitude of the P 300 is related to performance, as a function of detection rate and the complexity of the tasks. The functional duality of the CNV and the differences between it and the P 300 have been emphasized. The indices obtained from slow potentials appear to be of value for an evaluation of behaviour. Rather than analyzing the characteristics of the potentials in a supposedly "neutral" situation it would appear preferable to establish, from the indices, profiles of individual reactivity and adaptation to different experimental situations.
Action Potentials↗
[Study of CNV in patients with chronic respiratory insufficiency (author's transl)].
Chronic respiratory insufficiency (CRI) has physiological and psychological aspects that we have tried to examine with the CNV. The study is related to the CNV of 15 CRI patients and 14 control subjects (Cir.). The duration and amplitude of the CNV are more developed in CRI patients. The latter show an increased frequency of prolonged CNV and also a predominance of negative phenomena during the post-imperative period of the CNV. 'Delayed CNV' are very rare among CRI patients, but they are present among 60% of Ctr. subjects. The 'field dependency CNV' are not more frequent in either group. Various factors, most likely related to those CNV modifications, are discussed (aetiologies, chronicity, adaptation, personality).
Adult↗
[Quantified EEG and CNV changes during inhalation of nitrous oxide].
The present study constitutes an approach to the action mechanisms of nitrous oxide (N2O) by assessing both the subjective effects induced by the inhalation of this anaesthetic gas, and their electrophysiological correlates, i.e., spontaneous EEG, analyzed by a Fourier algorithm, AEP and CNV. The experiment was conducted single blind in 9 volunteers under 3 recording conditions: inhalation of air, of a mixture of 25% N2O--75% O2, and of a mixture of 50% N2O--50% O2. A latin-square design was used. Polymorphic effects of N2O were evidenced on behaviour and on CNS: some of the behavioural manifestations could evoke a depression of SNC: muscle relaxation with difficulty of motor initiation, psychomotor slowing, slower EEG with diminution of the percent alpha component and increase in the percent theta and delta, loss of amplitude of both exogenous (N1) and endogenous (P300) components of the AEP. Conversely, other manifestations were observed that are compatible with an activation of the CNS: increase of sensory perceptions, appearance of perceptual illusions, maintenance of a high CNV amplitude and lengthening of its duration. This dual effect of N2O suggests a dissociative action at the different levels of the CNS.
Adult↗
Self-regulation of slow cortical potentials in epilepsy: a retrial with analysis of influencing factors.
Twenty sessions of biofeedback training were carried out with 12 drug-resistant patients with focal epilepsy who learned to produce either negative or positive shifts of their slow cortical potentials (SCPs) at vertex. Feedback trials were interspersed with transfer trials in which only a discriminative stimulus (signalizing whether positivity or negativity was required) was presented, without feedback signal. Patients were able to differentiate significantly between the conditions of cortical positivity and cortical negativity, with larger differentiation scores being obtained in feedback trials than in transfer trials. The amplitude of positivity generated in the positivity condition increased linearly across sessions both in feedback and in transfer trials. The largest negativity was produced in the 5th session; after this, more transient negativities were generated, whose amplitude decreased towards the end of trial. The mean severity of seizures, estimated as the frequency of seizures weighted by their subjective 'strength', decreased significantly after training as compared to the pre-training phase. The data suggest that (1) patients could learn to achieve a state of cortical disfacilitation and (2) with progressed learning, they became less motivated for (or afraid of) producing considerable negative shifts, since extensive negativity may reflect cortical over-excitation and therefore be associated with early signs of seizures. The inability of producing cortical negativity is however not necessarily a bad predictor.
Adult↗
Discrepant target detection and action monitoring in obsessive-compulsive disorder.
Obsessive-compulsive disorder (OCD) has been related to altered mechanisms of action monitoring and target detection, and it has been hypothesized that hyperactive striatal-cortical circuits constitute the underlying pathophysiology. This study used event-related brain potentials (ERPs) to explore this hypothesis. A choice reaction time experiment was carried out in a group of OCD patients and a normal comparison group. The P3b component of the ERP to targets was taken as an indicator of the target-evaluation process and the response-locked error-related negativity (ERN) served as an indicator of action monitoring. We hypothesized that the OCD group would show a shortened P3b latency and an amplitude-enhanced ERN. Consistent with our expectations, the P3b latency was shorter and the ERN amplitude was higher in the OCD group. Unexpectedly, we also observed a prolonged ERN latency in the OCD group and a more posterior topography of this component. The data provide partial support for the hypothesis of a hyperactive neural network in OCD. In addition the disorder must involve pathophysiological processes that are presumably related to other aspects of its complex and heterogeneous clinical hallmarks.
Adult↗
Syntax-related ERP-effects in Dutch.
In two studies subjects were required to read Dutch sentences that in some cases contained a syntactic violation, in other cases a semantic violation. All syntactic violations were word category violations. The design excluded differential contributions of expectancy to influence the syntactic violation effects. The syntactic violations elicited an Anterior Negativity between 300 and 500 ms. This negativity was bilateral and had a frontal distribution. Over posterior sites the same violations elicited a P600/SPS starting at about 600 ms. The semantic violations elicited an N400 effect. The topographic distribution of the AN was more frontal than the distribution of the classical N400 effect, indicating that the underlying generators of the AN and the N400 are, at least to a certain extent, non-overlapping. Experiment 2 partly replicated the design of Experiment 1, but with differences in rate of presentation and in the distribution of items over subjects, and without semantic violations. The word category violations resulted in the same effects as were observed in Experiment 1, showing that they were independent of some of the specific parameters of Experiment 1. The discussion presents a tentative account of the functional differences in the triggering conditions of the AN and the P600/SPS.
Brain Mapping↗
Switching between simple response-sets: inferences from the lateralized readiness potential.
Behavioral studies have documented that task switching incurs a longer reaction time than task repetition, and that advance cueing information about the forthcoming task reduces mean reaction time. The present study used P300 peak latency and two lateralized readiness potential (LRP) intervals--stimulus-locked and response-locked--to infer the loci of task switch and task-cueing effects and how they may interact in the basic task processing chain. 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. In one condition, each stimulus was preceded by a cue informing participants which of the two tasks to perform; and in the other condition, each stimulus was preceded by a non-informative cue. Results indicated that both mean reaction times and the stimulus-locked LRP intervals were longer for switch than repeated trials, whereas P300 peak latencies and response-locked LRP intervals were identical for both trials. Similarly, both reaction times and the stimulus-locked LRP intervals were longer for no task-cueing than for task-cueing conditions, and P300 peak latencies and the response-locked LRP intervals were identical for both conditions. Finally, task switch and task-cueing effects appeared to be approximately additive, indicating the two factors influence distinct stage processes. We suggest that task switching resulted in prolongation of the response selection process by carry-over priming effects from the previous task, whereas task-cueing shortened the duration of the earlier process before response selection on both switch and repeated trials.
Adult↗
The early component of the premovement readiness potential and its behavioral determinants.
Fifteen healthy subjects were asked to randomly select a tick of a mechanical clock which was operating throughout the experiment and to flex their wrist at the chosen tick. The individual averages of EEG recordings collected during the period of the putative decision to begin the task exhibited steep slopes of negativity followed by plateaus. These slopes preceded the selection of the signal sound at varying intervals, the longest interval was 3 s. The grand average of individual averages depicted a waveform whose shape was identical to the early component of the classical readiness potential. Another interesting finding came from experiments with mental counting of clock sounds, which demonstrated that the generation of the first mentally-counted number is preceded by a distinct negative potential shift.
Acoustic Stimulation↗
Cortical processing of complex tone stimuli: mismatch negativity at the end of a period of rapid pitch modulation.
In this study, synthesised instrumental tones were used to examine human auditory cortical processes engaged at the end of a period of rapid pitch modulation. It was previously [S.J. Jones, O. Longe, M. Vaz Pato, Auditory evoked potentials to abrupt pitch and timbre change of complex tones: electrophysiological evidence of 'streaming'?, Electroencephalogr. Clin. Neurophysiol., 108 (1998) 131-142] suggested that the 'change-N1' produced by infrequent changes in pitch or timbre of a continuous complex tone represents the activity of a neuronal population topographically distinct from that responsible for the 'onset-N1' at the beginning of the tone. In the present study a superficially similar negativity was produced when the tone came to rest on a steady pitch after a period of rapid (8-16 changes/s) modulation; its scalp maximum was anterior to that of the two previously identified potentials but similar to that of the mismatch negativity elicited by discontinuous tones. By varying the modulation rate the latency was shown to be relatively constant with respect to the time the next pitch change was expected but failed to occur. The largest responses averaging c. 7 microV were evoked at the end of modulation sequences which were both rhythmic and repetitive, but a potential was still produced when there was no rhythmic pattern or repetition of individual notes. This response to non-occurrence of an expected but not necessarily specified change implies an automatic process for comparing the incoming sound with an extrapolated template of the preceding pattern in which timing as well as pitch information is accurately represented. We suggest this technique offers a robust method for eliciting the mismatch negativity, which may extend the opportunities for electrophysiological investigation of higher auditory processes.
Acoustic Stimulation↗
Searching for face-specific long latency ERPs: a topographic study of effects associated with mismatching features.
In a previous study [E. Olivares, M.A. Bobes, E. Aubert, M. Valdés-Sosa, Associative ERPs effects with memories of artificial faces, Cogn. Brain Res. 2 (1994) 39-48] we reported the presence of a negativity associated with mismatching features when subjects carried out a face-feature matching task whilst their evoked potentials were recorded. Since the stimuli used were learned faces (realistic drawings), for which the subjects possessed no semantic information or associated verbal labels, the mismatch negativity obtained was considered a face-specific N400. In this work we present a new experiment to study the topographic distribution of these mismatch effects. As in the above-mentioned study, in each trial the subjects observed previously an incomplete (without the eyes/eyebrows fragment) familiar face, which served as a structural context for the face recognition. The face was then completed by grafting either matching (learned) features or mismatching features (from another face). In line with neuropsychological studies on prosopagnosia and electrophysiological findings in humans and non-human primates, we found as one of the most relevant items of data that the most-posterior (principally, left occipital) cortices appear to be a region in which are located the possible neural generators of the negativity associated with the detection of incongruencies in the structure of familiar faces. We also reported a late positivity, distributed in more anterior regions, which follows the mismatch negativity. This complex N-P is interpreted as reflecting a dual process of retrieval and integration of information in memory.
Adult↗
Pre-attentive detection of vowel contrasts utilizes both phonetic and auditory memory representations.
Event-related brain potentials (ERP) were recorded to infrequent changes of a synthesized vowel (standard) to another vowel (deviant) in speakers of Hungarian and Finnish language, which are remotely related to each other with rather similar vowel systems. Both language groups were presented with identical stimuli. One standard-deviant pair represented an across-vowel category contrast in Hungarian, but a within-category contrast in Finnish, with the other pair having the reversed role in the two languages. Both within- and across-category contrasts elicited the mismatch negativity (MMN) ERP component in the native speakers of either language. The MMN amplitude was larger in across- than within-category contrasts in both language groups. These results suggest that the pre-attentive change-detection process generating the MMN utilized both auditory (sensory) and phonetic (categorical) representations of the test vowels.
Acoustic Stimulation↗
Magneto-encephalographic correlates of the lateralized readiness potential.
To determine the onset of movement-related EEG activity accompanying stimulus-induced movements, it is commonly isolated from overlapping stimulus-related activity by a subtraction procedure, yielding the lateralized readiness potential (LRP). In order to elucidate the generation of the LRP and to explore whether magnetoencephalographic (MEG) measures have advantages over the LRP as a measure of response selection, MEG activity was recorded in four healthy adults during self-paced and stimulus-induced hand movements. Self-paced movements were preceded by readiness fields in all subjects, explained by sources in contralateral and (for 2/8 response sides) also ipsilateral hemispheres. Movement-related activity preceding stimulus-induced movements could only be modeled adequately when stimulus-related activity was removed by subtracting MEG signals for left and right hand movements. Thus identified source locations showed no systematic deviation from the sources for readiness fields, supporting a generation of the movement-related activity in primary motor cortex. The corresponding source waveforms allowed latency determinations of motor cortex activity as markers for response-choice timing. MEG thus provides information on the time course of hand-specific motor cortex activation for each hemisphere separately, where the electro-encephalographic LRP provides a composite measure for both hemispheres.
Adult↗
[Spatiotemporal study of event-related desynchronization during self-paced movement].
The desynchronization of Alpha band components during a self-paced movement of the thumb was studied in 7 subjects. The EEG was recorded from 23 electrodes located on the frontocentral, central, and parietocentral regions, referred to the right mastoïde, 4 s before and 2 s after movement onset. The data were then transformed to obtain 11 source derivations. The temporal evolution of the power of the signal within the Alpha band, every 250 ms, associated to the non parametric statistic test of Wilcoxon, authentifies the event-related desynchronization (ERD). The spatiotemporal analysis of ERD underlines on the central regions, two principal locations of ERD: one controlateral to the movement, starting more than 1 s before the movement; the other, ipsilateral, shorter, during the movement. However, no significance desynchronization was underlined on the vertex. The ANOVA used to analyse these results confirms the principal location of ERD on the central region, and seems to indicate a right lateralisation during the right or the left movement.
Adult↗