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PubMed1989

Effect of DSP4, a neurotoxic agent, on attentive behaviour and related electrocortical activity in cat.

Six behaving cats were administered N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4) (i.p. 10 mg/kg), a neurotoxic agent known to destroy noradrenergic endings in the CNS. They were placed, both before (control) and after treatment in 3 different situations, each time for 90 min: (1) a 'neutral' one (N) with no significant stimuli; (2) another one eliciting focused attention (F); (3) a third one, creating a situation of 'expectancy of an event to occur' (E), with the animal usually displaying a posture of quiet waking. Simultaneously, the electrocorticogram (ECoG) was recorded from the sensorimotor and parietal cortex through implanted electrodes. We already knew and were able to confirm that the normal animals (i.e. before treatment) displayed distinct behavioural patterns depending on the situation and distinct accompanying parietofrontal ECoG activities, with a dominance of drowsiness and sleep during N, that of a 36-Hz 'beta' rhythms in condition F, and of 14-Hz 'mu' rhythms in condition E. It was shown that the prevailing attitude of the animals after treatment was now, in all 3 situations, that of 'quiet waking and/or expectancy-like watching', with a large if not exclusive dominance of only one ECoG pattern, namely mu. These changes were considered as due to a release of the mu system from a noradrenergic modulatory blockade, in accordance with some of our previous data. An immunohistochemical study with anti-tyrosine hydroxylase antibody was also performed; it confirmed that after DSP4 treatment there were substantial alterations in the immunoreactivity of locus coeruleus cells, the structure which is likely to be involved in this NAergic control of the mu rhythms and of its concomitant behaviour.

Animals↗
PubMed2001

Anticipatory attention: an event-related desynchronization approach.

This paper addresses the question of whether anticipatory attention--i.e. attention directed towards an upcoming stimulus in order to facilitate its processing--is realized at the neurophysiological level by a pre-stimulus desynchronization of the sensory cortex corresponding to the modality of the anticipated stimulus, reflecting the opening of a thalamocortical gate in the relevant sensory modality. It is argued that a technique called Event-Related Desynchronization (ERD) of rhythmic 10-Hz activity is well suited to study the thalamocortical processes that are thought to mediate anticipatory attention. In a series of experiments, ERD was computed on EEG and MEG data, recorded while subjects performed a time estimation task and were informed about the quality of their time estimation by stimuli providing Knowledge of Results (KR). The modality of the KR stimuli (auditory, visual, or somatosensory) was manipulated both within and between experiments. The results indicate to varying degrees that preceding the presentation of the KR stimuli, ERD is present over the sensory cortex, which corresponds to the modality of the KR stimulus. The general pattern of results supports the notion that a thalamocortical gating mechanism forms the neurophysiological basis of anticipatory attention. Furthermore, the results support the notion that Event-Related Potential (ERP) and ERD measures reflect fundamentally different neurophysiological processes.

Acoustic Stimulation↗
PubMed2002

Phase-coupling of theta-gamma EEG rhythms during short-term memory processing.

Because of the importance of oscillations as a general phenomenon of neuronal activity the use of EEG spectral analysis is among the most important approaches for studying human information processing. Usually, oscillations at different frequencies occur simultaneously during information processing. Thus, the question for synchronisation of different frequencies by phase coupling and its possible functional significance is of primary importance. An answer may be given by bispectral analysis. Estimation of the (cross-) bispectrum allows to identify synchronised frequencies and possibly, the existence of non-linear phase coupling of different oscillators. Previous studies have demonstrated the simultaneous occurrence of slow (4-7 Hz) and fast (20-30 Hz) oscillations at frontal and prefrontal electrode positions during memory processing. However, interrelations between these rhythms have not been investigated up to now. In order to test short-term memory, the Sternberg task with random figures and number words was carried out on 10 female subjects. During the task EEG was recorded. Power and bispectral analyses from frontal, prefrontal and frontopolar regions were performed off-line. Increased power was found in both the theta and the gamma bands. Strong phase-coupling between theta at Fz and gamma at F3 and at Fp1, respectively, was shown for memorising number words by means of cross-bicoherence. A possible reason for this is an amplitude modulation of gamma frequencies by slow oscillations. The correspondent coherence analysis between the envelope of gamma frequencies at Fp1 and the raw EEG at Fz supports this presumption. This finding is interpreted as an EEG aspect of the functional linking between the prefrontal areas and the G.cinguli (as part of the limbic system), which are both extremely important for memory functions.

Adult↗
PubMed1996

The reliability of event-related desynchronisation: a generalisability study analysis.

The aim of this study was to examine the spatio-temporal reliability of EEG power during the baseline period of an event-related desynchronisation (ERD) experiment. The data were analysed using ideas from generalisability theory. The largest sources of variance were found to be associated with differences between subjects (subject main effect), and to idiosyncratic topographical distributions (subject x electrode interaction). The resulting spatio-temporal reliabilities exceeded 0.7, except in theta and the absolute power values were relatively stable. Overall, this study gives further support for the reliability of quantitative EEG measures in general and for the method of ERD in particular.

Adult↗
PubMed1996

Event-related desynchronization (ERD) and the Dm effect: does alpha desynchronization during encoding predict later recall performance?

Based on previous research which has shown that event-related desynchronization (ERD) in the lower and upper alpha band reflects attentional and semantic processing respectively, the present study examines the hypothesis whether event-related shifts in the two alpha bands are capable of predicting later recall performance. In an incidental memory paradigm, subjects first had to judge the category membership for a set of 96 words. Later, without prior warning, subjects were asked to recall the words. The results show that for good performers, the extent of ERD in the lower alpha band during the semantic encoding for words is significantly larger for remembered as compared to not remembered words, whereas for bad performers the ERD in the upper alpha band is significantly more pronounced. This type of Dm effect is particularly strong over parietal recording sites in both hemispheres. In referring to the proposed interpretation of the lower and upper alpha band, the present findings seem to indicate that in contrast to good performers, bad performers are less attentive or alert during encoding. Event-related potentials (ERPs) also yielded significant Dm effects at parietal recording sites.

Adult↗
PubMed1996

Pre- and post-stimulus processes in affective task and event-related desynchronization (ERD): do they discriminate anxiety coping styles?

The present investigation was designed to study whether pre-stimulus (as measured by EEG power in the time interval before the stimulus presentation) and post-stimulus (as measured by event-related desynchronization (ERD)) processes of alpha components in two frequency bands (8-10 and 10-12 Hz) and their scalp distribution discriminate among anxiety coping styles in an affective task. We investigated this question by using a sample of 30 college students who were split into three groups consisting of 10 low-anxious (LA) and 10 high-anxious (HA) subjects, and 10 repressors (RE). In the present study, positive and negative emotions were operationalized by winning and losing certain amounts of money in gambling situation while measuring ERD to positive and negative feedback stimuli. The main findings of the prestimulus data analyses suggest that the prestimulus level of alpha power is sensitive to the anxiety coping styles. In terms of ERD effects, HA individuals were marked by relatively larger left-hemisphere activation compared to low-anxious subjects and repressors. Further, in contrast to LA and RE, the phenomena observed in our experiment of increased and extended ERD over time in HA in response to negative feedback stimulation implies that threatening information (loss of money) is more persistently activated in subjects with high anxiety. Although preliminary, the reported findings are of potential importance because they could lead to the development of a new psychophysiological measure of relevance to personality.

Adaptation, Psychological↗
PubMed1999

The sensitivity of instantaneous coherence for considering elementary comparison processing. Part II: Similarities and differences between EEG and MEG coherences.

The EEG (electroencephalogram) coherence depends on EEG deviation type. A high level of sensitivity of instantaneous coherence for investigating elementary cognitive tasks could be shown in the case of unipolar reference (ear lobe reference). In order to validate of this result the same investigations were performed for MEG (magnetoencephalogram) coherence, where EEG and MEG were measured simultaneously. A strong correlation between time intervals with high EEG and MEG coherence could be shown. The equivalence of the sensitivity of EEG and MEG coherence for the description of the dynamic behaviour of information processing and the distinction between different elementary cognitive tasks is proven statistically.

Adult↗
PubMed2002

Long-term enhancement of excitatory synaptic inputs to layer V parahippocampal neurons by low frequency stimulation in rat brain slices.

Excitatory inputs to layer V neurons of the parasubiculum and medial entorhinal cortex were examined in rat brain slices with intracellular and field potential recordings. Single extracellular stimuli to layer V evoked subthreshold excitatory postsynaptic potentials (EPSPs) or a long duration (>100 ms) depolarization that sustained high frequency firing. Repetitive stimulation at low frequencies (from 1/10 s to 1/min) induced stable long-lasting decreases in the threshold for firing in individual cells or population events, and also induced stable long-lasting increases in evoked intracellular or field response amplitudes. More stimuli were required to produce the equivalent changes in threshold and amplitude in the presence of MCPG (200 microM). Smaller changes in amplitude, but equivalent changes in threshold were elicited in the presence of CPP (10 microM), or CPPG (20 microM). No changes in threshold or amplitude were detected in the presence of CNQX (10 microM), even when used in combination with picrotoxin (100 microM). EPSP facilitation was enhanced greatly by firing in postsynaptic cells. It is suggested that stable changes in excitatory inputs to layer V parahippocampal neurons involve the activation of NMDA and metabotropic glutamate receptors, but requires AMPA receptor activation and postsynaptic cell firing.

Action Potentials↗
PubMed1998

A method for the calculation of induced band power: implications for the significance of brain oscillations.

A method for the calculation of significant changes in induced band power (IBP) is presented. In contrast to traditional measures of event-related band power (ERBP) which are composed of evoked and not evoked EEG components, the proposed measure for IBP is deprived from phase locked (or evoked) EEG activity. It is assumed that changes in IBP reflect the modulation of brain oscillations that are largely independent from ERPs. The results of a visual oddball task show that significant changes in IBP can be observed in response to the presentation of a warning signal (preceding a target or nontarget) and the imperative stimulus (i.e. a target or nontarget) in the alpha, theta and delta band. Only a few significant changes in IBP were obtained for the warning signal in the theta band although highly significant changes in ERBP were found. Our findings document that changes in IBP may be considered a phenomenon that is largely independent from the occurrence of ERPs. They underline the significance of oscillatory processes and suggest that induced rhythms are modulated by stimuli and/or events in a not phase locked way.

Adult↗
PubMed2001

Event-related beta desynchronization indicates timing of response selection in a delayed-response paradigm in humans.

Voluntary movements are preceded by event-related desynchronization (ERD) of alpha and beta activity. The present study used magnetoencephalography to investigate the relationship between motor preparation and the time course of beta ERD in a delayed response paradigm. Depending on the task, the required response (left or right finger lifting) was cued either spatially by the lateralization of a sound at trial onset, or verbally by the content of a midline auditory event. Beta ERD appeared over sensorimotor regions contralaterally to the response side about 200 ms earlier for the spatial than the verbal cue task. This suggests a close relationship between the latency of beta ERD onset and the duration of cognitive processes involved in selecting a motor response.

Acoustic Stimulation↗
PubMed2001

Magnetoencephalography and stereopsis: rhythmic cortical activity in humans recorded over the parieto-occipital cortex.

We have studied human stereopsis by analysing magnetoencephalographic signals during the presentation of stereograms using frequency analysis. The study of synchronised firing of cortical neurones is a new way of understanding information processing in the brain and it is hypothesised that frequencies greater than 35 Hz are used for higher-order processing. We report the response of cortical neurones involved in stereopsis recorded from over the occipital and parietal cortices using a single channel axial superconducting quantum interference device neuromagnetometer. Our main result was increased cortical activity in the gamma-band at frequencies apparently related to stereopsis and the perception of depth. Our results are consistent with reports in the literature that suggest that frequencies above 40 Hz are involved in attention, pattern recognition and higher order visual activity.

Adult↗
PubMed2002

The effects of probability and relative direction on human somatomotor electroencephalographic rhythms.

Classical views on the preparation of voluntary movement involve separate motor and cognitive processes. Recent neurophysiological evidence challenges this dichotomy. Recordings from within the motor cortices have demonstrated that cognitive factors modulate neural activity. This issue was examined in event-related desynchronizations (ERDs) by using a goal-directed pointing paradigm. The ERD, which is typically recorded in response to self-paced finger movements, has been demonstrated to reflect specific movement parameters. Cognitive factors were introduced by manipulating probability and the relative direction of the responses in a choice reaction time task. The results demonstrated that probability influences the 20 Hz ERD.

Cognition↗
PubMed2002

Parallel distributed processing neuroimaging in the Stroop task using spatially filtered magnetoencephalography analysis.

Parallel distributed processing neuroimaging in the Stroop color word interference task in five healthy subjects was studied. The total reaction time was set at 650 ms with a time window of 200 ms in steps of 50 ms. Spatially filtered magnetoencephalography analysis, as used in synthetic aperture magnetometry, was used. Neural activation began in the left posterior parietal-occipital area (150-250 ms post-stimulus), followed by the right prefrontal polar area (250-350 ms), the left dorsolateral prefrontal cortex (250-400 ms), and the mid- to lower- primary motor area (350-400 ms). Successive and temporally overlapping activation of various cortical regions were successfully estimated within a short 200 ms time interval, contrary to previous positron emission tomography and fMRI studies.

Adult↗
PubMed1997

Motor imagery activates primary sensorimotor area in humans.

The spatiotemporal patterns of Rolandic mu and beta rhythms were studied during motor imagery with a dense array of EEG electrodes. The subjects were instructed to imagine movements of either the right or the left hand, corresponding to visual stimuli on a computer screen. It was found that unilateral motor imagery results in a short-lasting and localized EEG change over the primary sensorimotor area. The Rolandic rhythms displayed an event-related desynchronization (ERD) only over the contralateral hemisphere. In two of the three investigated subjects, an enhanced Rolandic rhythm was found over the ipsilateral side. The pattern of EEG desynchronization related to imagination of a movement was similar to the pattern during planning of a voluntary movement.

Adult↗
PubMed1999

Force level modulates human cortical oscillatory activities.

We studied the relationship between cortical and muscular oscillatory activities and muscular force level during a tonic contraction task using electroencephalography (EEG). Within the weak to moderate force level, the normalized power in the alpha band in the contralateral sensorimotor areas was inversely linearly correlated with the force. Cortical-muscular coherence was observed in the beta band and its magnitude was not affected by the force. In contrast, during strong contractions, EEG power in the gamma band increased and was partly correlated with the Piper rhythm in the electromyogram. Our results show that the multiple oscillatory activities in the cortex are correlated with the force level in different ways. Cortical gamma band oscillation may reflect both focused attention and the efferent drive to the muscle during very strong tonic contraction.

Adult↗
PubMed2003

Spontaneous field potentials influence the activity of neocortical neurons during paroxysmal activities in vivo.

Field-potential recordings with macroelectrodes, and extra- and intracellular potentials with micropipettes were used to determine the influence of spontaneous field potentials on the activity of neocortical neurons during seizures. In vivo experiments were carried out in cats under anesthesia. Strong negative field fluctuations of up to 20 mV were associated with electroencephalogram "spikes" during spontaneously occurring paroxysmal activities. During paroxysmal events, action potentials displayed an unexpected behavior: a more hyperpolarized firing threshold and smaller amplitude than during normal activity, as determined with intracellular recordings referenced to a distant ground. Considering the transmembrane potential (the difference between extra- and intracellular potential) qualified this observation: firing threshold determined from the transmembrane potential did not decrease, and smaller action-potential amplitude was associated with depolarized firing threshold. The hyperpolarization of intracellular firing threshold was thus related to the field potentials. Similar field-potential effects on neuronal activities were observed when the paroxysmal events included very fast oscillations or ripples (80-200 Hz) that represent rapid fluctuations of field potentials (up to 5 mV in <5 ms). Neuronal firing was phase-locked to those oscillations. These results demonstrate that: (a) strong spontaneous field potentials influence neuronal behavior, and thus play an active role during paroxysmal activities; and (b) transmembrane potentials have to be used to accurately describe the behavior of neurons in conditions in which field potentials fluctuate strongly. Since neuronal activity is presumably the main generator of field potentials, and in return these potentials may increase neuronal excitability, we propose that this constitutes a positive feedback loop that is involved in the development and spread of paroxysmal activities, and that a similar feedback loop is involved in the generation of neocortical ripples. We propose a mechanism for seizure initiation involving these phenomena.

Animals↗