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PubMed1985

Anticipatory response-relevant muscle activity, CNV amplitude and simple reaction time.

The present experiment was aimed at whether subjects, performing a forewarned simple reaction time (RT) task, do voluntarily tense agonist and antagonist muscles during the foreperiod; if so, would such muscle tension co-vary with CNV amplitude or RT? Although excessive eye movements caused 30% of the subjects to be removed from the analysis, it was still possible after the experiment to differentiate between subjects who gradually tensed their agonist during the foreperiod and subjects who did not. The former group showed higher CNV early and late wave amplitudes as compared with the latter group. A similar effect was found on the N1 amplitude of the potential evoked by the warning stimulus. The increased EMG in the agonist muscle at the end of the foreperiod was not concomitant with faster RTs. In addition, fast RTs were preceded by higher CNV late wave amplitudes at pre- and postcentral electrode positions. The observed relationships between CNV, EMG, and RT were discussed in terms of specific and general motor preparation.

Adolescent↗
PubMed1986

Terminal CNV in the absence of motor response.

We addressed the question of whether the terminal CNV, or E-wave, can be obtained in the absence of a motor response. In our design, the stimuli served only to reduce uncertainty with respect to a prior prediction, so that no response to S2 was required. In one experiment, the location of uncertainty reducing information was manipulated: in S1 alone or in S2 alone. When S2 reduced uncertainty, the pre-S2 E-wave was larger than when S2 did not reduce uncertainty. Similarly, when S1 reduced uncertainty, a pre-S1 negativity (whose topography did not differ from that of the pre-S2 E-wave) was larger than when S1 did not reduce uncertainty. The pre-S1 results also indicated that a prior experimenter-generated warning signal is not necessary for a non-motoric negativity to be obtained. In another experiment, the S1-S2 interval was manipulated (1 sec versus 3 sec). For the pre-S2 E-wave, onset was later and duration was longer for the longer S1-S2 interval. Peak amplitude and time of termination after S2 did not differ for short and long duration E-waves. Apparently, the timing of the E-wave is related to when in time the process it reflects is 'needed.' The dependence of the amplitude and timing of the pre-stimulus negativity on the temporal location of information, in conjunction with its independence of motor response requirement, suggests that the pre-stimulus negativity reflects some operation in the domain of expectancy, anticipation or 'mental preparation' for the informational stimulus.

Adolescent↗
PubMed1987

Differences between REM and NREM sleepiness measured by event-related potentials (P300, CNV), MSLT and subjective estimate in narcolepsy-cataplexy.

Differences between 'REM sleepiness' and 'NREM sleepiness' states in wakefulness studied respectively prior to REM-containing and NREM-only multiple sleep latency test (MSLT) naps were compared by complex evoked potentials (P300, CNV), subjective estimate (Stanford Sleepiness Scale, SSS) and MSLT measures in 12 untreated patients with narcolepsy-cataplexy. The EP paradigms lasted about 7 min each and were done during the 10 min immediately before MSLT naps at 10.00, 12.00, 14.00, 16.00 and 18.00 h. SSS forms were completed immediately before and after the EP studies and MSLT naps. Patients were studied on 2 days and performed either the P300 or CNV paradigm on each day. 'REM sleepiness' was found to be subjectively and objectively (shorter mean sleep latency on MSLT) greater. Although subjects were sleepier in REM sleepiness, the subsequent REM nap was relatively more refreshing and reduced SSS estimates to levels equivalent to those after NREM-only naps. EP measures also showed differences between the 2 sleepiness states. REM sleepiness was associated with a significantly larger P2 component (in both the P300 paradigm and the CNV paradigm), a strong but not significant trend towards reduced amplitude of the P3 component, and almost total suppression of the slow negative components of the CNV. REM sleepiness and NREM sleepiness therefore appear to be district and differentiable cerebral states.

Adult↗
PubMed1987

Cocaine effects on electroencephalographic cognitive event-related potentials and performance.

The effects of cocaine on electroencephalographic indices, information processing and motor performance were measured in 12 normal volunteers. They were tested with an auditory continuous performance task before, 60 and 180 min after a 3 mg/kg oral dose of cocaine hydrochloride or placebo in a double-blind counterbalanced crossover design. EEG from Fz, Cz and Pz were averaged for the eye movement-free correct trials. N100, P200, P300 components and CNV were measured. Cocaine increased N100 amplitude for the warning stimulus and CNV amplitude. P300 amplitude and latency, reaction time and sensory sensitivity (d') were not altered by cocaine. The increase in N100 and CNV amplitude may reflect mobilization of additional attentional resources to produce optimal performance on the task when subjects were distracted by the cardiovascular, subjective and other cocaine effects.

Adult↗
PubMed1988

Distribution of slow brain potentials related to motor preparation and stimulus anticipation in a time estimation task.

Subjects had to press a button at regular intervals of 20 sec. Two seconds after each button press a stimulus was presented indicating the length of the past interval. EEG was analysed from 2500 msec preceding the button press until the presentation of the stimulus. Preceding the button press a readiness potential (RP) was recorded with amplitudes that were larger over the hemisphere contralateral to the movement side. Preceding the stimulus negative waves were recorded which were larger over the right hemisphere, irrespective of the movement side. In a warned reaction time experiment, the CNV late wave represents both motor preparation and stimulus anticipation. In the present study motor preparation and stimulus anticipation are no longer confounded factors. Thus, it is shown that stimulus anticipation is indeed reflected by negative activity, as is motor preparation. The potential distribution of the RP, however, is different from the stimulus-preceding negativity (SPN), a pointing to a different electrophysiological source. The potential distribution of the SPN has been investigated and a right hemisphere preponderance of the SPN has been found.

Adolescent↗
PubMed1991

Effects of the anticonvulsant benzodiazepine clonazepam on event-related brain potentials in humans.

The effects of the benzodiazepine clonazepam (a drug used as anticonvulsant) on event-related brain potentials were investigated in healthy human subjects. Thirty-six male student volunteers (mean age 30 years) received clonazepam or a placebo in a double-blind setting. VEPs (visual evoked potentials) were obtained from the standard checkerboard reversal procedure; AEPs (auditory evoked potentials) and slow cortical potentials (CNV) were measured during a 2-stimulus reaction time paradigm, in which the quality of the acoustic S1 signalled whether the acoustic S2 would follow after 2 sec or after 6 sec. Each S2 requested a speeded button press. Compared to placebo, clonazepam significantly reduced P100 amplitude of the VEP and the amplitudes of the AEP components N1 and P3. On the other hand, clonazepam boosted the development of a distinct N2 which was not apparent in placebo subjects. The CNV was significantly reduced and reaction time increased under clonazepam compared to placebo. Specific versus non-specific damping effects of the benzodiazepine are discussed, comparing the present result with the pattern of ERP effects of the anticonvulsant carbamazepine that had been obtained using the same experimental paradigms.

Adult↗
PubMed1991

Reduced attention-related negative potentials in schizophrenic children.

ERPs were recorded from normal and schizophrenic children during performance of a reaction time task (RT) followed by a complex visual discrimination, the span of apprehension task (Span), sensitive to vulnerability factors in schizophrenia. Subjects responded rapidly to the onset of the visual arrays in the RT condition and differentially to the presence of 1 of 2 target letters in the Span condition. The EEG was recorded at 19 scalp sites and ERPs included activity 1 sec before through 1 sec after Span array onset. Difference potentials (Span-RT) were computed to remove unvarying exogenous activity, thus isolating endogenous activity associated with the processing demands of the Span task. When RT and Span task ERPs are compared, schizophrenic children produced a significantly smaller than normal increment in endogenous negative activity. This endogenous negativity differed in its topography and time course from the exogenous components (P1, N1 and P2), and most likely reflects attentional effort associated with serial search, pattern recognition and stimulus identification. We believe that the current results support the position that schizophrenics are impaired in their ability to allocate adequate attentional resources for the processing of the Span stimuli. It is important to note that this deficit is apparent quite early in discriminative processing.

Analysis of Variance↗
PubMed1992

Frontocentral DC-potential shifts predicting behavior with or without a motor task.

This study was designed to investigate the predictive value of the event-related potentials (ERPs) preceding the initiation of a difficult perceptual-memory task and to investigate whether these ERPs require a motor movement on the part of the subject for their occurrence. Across 4 conditions the DC-potential shifts were recorded from 23 right-handed subjects using DC amplifiers. Although the start of each trial began with a ready signal, the conditions differed in that the subjects initiated the task by a button press in 2 conditions and the computer initiated it in 2 others without a press. The results showed that, especially in the frontocentral electrode sites, the DC-potential shifts which began those trials ending in correct performance were more negative relative to those trials ending in an incorrect response. Those conditions which required the subjects to self-initiate the trial and those which were initiated by the computer showed similar results indicating that the negative DC-potential shifts preceding correct performance are neither produced by nor depend on a task initiating motor movement. The onset of the DC-potential shifts preceded task initiation by up to 4.1 sec indicating that they were more than the Bereitschaftspotential.

Adult↗
PubMed1992

Dependence of presaccadic cortical potentials on the type of saccadic eye movement.

Premovement cortical potentials were studied with 4 types of saccadic eye movement: (a) visually triggered saccades of normal reaction time (RT; regular saccades); (b) visually triggered saccades of extremely short RT (express saccades); (c) saccades towards predicted target locations (anticipatory saccades); (d) saccades back towards predicted location of fixation point (refixation saccades). With all 4 saccade types a "presaccadic negativity" with the maximum at the vertex (Cz) was observed. A bilaterally symmetrical component contained in this potential (being smallest with almost unconsciously performed refixation saccades and smaller in trained than in naive subjects) appeared to be related mainly to the subjects' volitional effort. In addition, anticipatory and refixation saccades were preceded by an early, widespread contralateral negativity, which we relate to cortical activities that prepare, in general terms, action within or towards the hemifield containing the saccade goal. During the 60 msec before anticipatory saccades, a negativity occurred over the contralateral central lead, which may reflect neural activation in the frontal eye field (FEF) and premotor cortex. In contrast, regular saccades were preceded 30 msec before onset by a negativity over the contralateral parietal cortex, which probably reflects an activation of parietal visuo-motor neurons. No lateralization of the cortical potentials was observed before express saccades, which suggests that these saccades are generated in a reflex-like way mainly by subcortical mechanisms.

Adult↗
PubMed1993

"Probing" the nature of the CNV.

A widespread depolarization in the dendritic trees of cortical pyramidal neurons generates surface-negative potentials. In turn, such potentials may indicate facilitatory processes, while positive-going waves may result from a lowering in cortical excitability. Accordingly, we may expect the processing of "probe" stimuli presented during surface-positive waves, i.e., during phases of lesser excitability, to be inhibited and probes presented during surface-negative waves to be facilitated. This hypothesis was tested by presenting acoustic probe stimuli at various points in time during a forewarned reaction time task. The warning stimulus (WS) elicited a late positive complex followed by a negative slow potential shift (CNV). In 75% of the total of 120 trials a probe could be presented 1.5 sec prior to the WS interval, 0.5, 1, 1.5 or 2 sec after the onset of the 3 sec visual WS, and 3 sec following the imperative signal (WS offset, requiring a fast button press response), while 25% of the trials were without any probe. Only one probe occurred during a trial. The EEG was recorded along the midsagittal line; responses to the probes were evaluated by reaction time (RT) and probe-evoked potentials. RT to probes presented late in the anticipatory interval were speeded up and probe-evoked potentials were enhanced during this interval, in parallel to the development of the slow potential and the CNV in particular. Results suggest that probe stimuli presented during the development of the CNV were processed more intensely, thereby supporting the hypothesis that slow cortical potentials indicate the timing of excitability in cortical neuronal networks.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1995

Readiness to respond in a target detection task: pre- and post-stimulus event-related potentials in normal subjects.

Brain potentials were recorded from 12 normal subjects engaged in an auditory target detection task (target stimulus probability of 0.2, stimulus rate of 1 every 2 sec) when instructions were (1) to press a response button with the thumb of the dominant hand to each target or (2) to keep a mental count of each target. A pre-stimulus slow negative potential was identified before every stimulus except non-targets immediately after targets. The amplitude of the pre-stimulus negativity was significantly affected by task instructions and was up to 4 times larger during the button press than the mental count condition. In contrast, the amplitudes and latencies of the event-related components (N100, P200, N200 and P300), when slow potentials were removed by filtering, were not different as a function of press or count instructions. The immediately preceding stimulus sequence affected both the amplitude and onset latency of the pre-stimulus negativity; both measures increased as the number of preceding non-targets increased. The amplitude of the pre-stimulus negative shift to targets also increased significantly as RT speed decreased. The major portion of the pre-stimulus negative potential is considered a readiness potential (RP) reflecting preparations to make a motor response. The amplitude of the RP during the target detection task did not significantly lateralize in contrast to the RP accompanying self-paced movements.

Adult↗
PubMed1995

Frequency and phase characteristics of slow cortical potentials preceding bimanual coordination.

The aim of the present study was to derive quantities which relate behavioral and neurophysiological levels of observation during a bimanual coordination task. We recorded the scalp electroencephalographic (EEG) signal preceding a sequence of 4 bimanual finger flexions of varying response rates in 12 subjects. A slow negative-going Bereitschaftspotential (BP) displayed larger mean amplitudes and earlier onset times for the faster required response rates. The amplitude of the BP was also larger for electrode locations contralateral to the side initiating the behavioral response. A Fourier transform showed two predominant frequencies (0.5 and 2.0 Hz) to be amplitude modulated as a function of the required response rate in addition to increased power on the contralateral side of the finger initiating the response. A measure of the phase relationship between the left (C3) and right (C4) hemispheres of the fronto-central cortex at each of these spectral frequencies was calculated as well as the variance in this measure and found to correspond closely to the variance in inter-response times derived from the subjects' movements. These findings indicate that changes in the stability and rate of a patterned movement are generally preceded by similar changes in the stability and amplitude of components observed on the neurophysiological level.

Acoustic Stimulation↗
PubMed1995

Abnormalities of the Bereitschaftspotential and MRI pallidal signal in non-encephalopathic cirrhotic patients.

In cirrhotic patients, even in the non-encephalopathic state, MRI may show an increased signal in globus pallidus in T1-weighted sequences, the clinical significance of which is still poorly characterized. A dysfunction of the motor circuit of the basal ganglia might be predicted if the increased MRI signal expressed alterations in the globus pallidus activity. We compared the Bereitschaftspotential (BP) in 15 non-encephalopathic cirrhotic patients and 15 age-matched controls and found that the amplitude of the early component and the peak negativity of the BP before the electromyogram onset were significantly reduced in the patient group. The intensity of the pallidal signal was related to the plasma ammonia level but the amplitudes of the BP were not related to the pallidal signal or to ammonia. These findings indicate that a defective activity of the cortical areas implicated in the preparation of movement, not specifically related to the pallidal signal, can be present in cirrhotic patients, even in the non-encephalopathic state.

Adult↗
PubMed1994

The presaccadic cortical negativity prior to self-paced saccades with and without visual guidance.

The presaccadic negativity (PSN) of the scalp EEG potential prior to self-initiated saccades aimed either at a visual target or at the remembered position of that target in total darkness was analysed in 10 normal subjects. Under both conditions a PSN with a negligible EOG contamination was found, showing 4 characteristics: (1) In both conditions, the PSN maximum is localized at the vertex, probably containing the activity of the supplementary motor area. (2) At an electrode placed over the frontal eye field (FEF) contralateral to the saccade direction, there is a temporary, circumscribed maximum prior to saccades to the visual target, thus probably reflecting activity of the FEF. (3) Prior to saccades to the visual target, there is a statistically significant interhemispheric difference of the PSN over the parietal cortex with a larger amplitude over the hemisphere contralateral to the saccade direction; this might be attributed to directed visual attention. (4) Prior to saccades without visual guidance in darkness there is a statistically significant interhemispheric difference of the PSN over the frontal cortex with a larger amplitude over the hemisphere contralateral to the saccade direction. The amplitude of the PSN decreased in the course of the experiment, probably due to psychological factors such as attention and motivation. Our results suggest that the PSN is a readiness potential preceding voluntary saccades, containing activity related both to unspecific psychological processes and to specific movement preparation in the frontal and parietal ocular motor areas.

Adult↗
PubMed1994

Intracerebral recording of movement related readiness potentials: an exploration in epileptic patients.

Readiness potentials (RPs) preceding voluntary self-paced limb movements were recorded intracerebrally in 13 patients suffering drug resistant, intractable epilepsy. Multilead depth electrodes were positioned using the Talairach's coordinate system; they allowed simultaneous recording from the external and mesial cortices and from the interposed white matter during self-paced unilateral hand or plantar flexions. Our intracerebral explorations have shown RPs in the primary motor cortex (MC) contralateral to the movement and in both supplementary motor areas (SMAs), indicating that at least 3 cortical sites become active before the movement. At variance with the scalp RPs recorded in the same patients, the intracerebral potentials were either negative, or positive, depending on the recording site. No consistent differences in duration and time of onset could be established between the MC and the SMA RPs, at least with the used time resolution. RPs were only occasionally observed in the parietal cortex and hippocampus and none were recorded from the amygdala, the temporal, temporo-occipital, prefrontal, frontal and cingular cortices. The wide topographical distribution of the scalp RPs may not be fully explained by the above intracortical findings, leaving the possibility that other generators exist, whose locations remain to be determined.

Adolescent↗
PubMed1994

A spatio-temporal dipole model of the readiness potential in humans. I. Finger movement.

Preceding unilateral finger movements readiness potentials (RPs) were recorded in 9 right-handed subjects. The data are presented as time series, potential maps and spatio-temporal dipole models. The latter are interpreted with respect to the underlying generators of the RP. Explicit hypotheses about the unilateral or bilateral activation of particular sensorimotor areas preceding unilateral movements are addressed. The choice for the best spatio-temporal dipole model was guided by a test on the orthogonality of the individual residuals and by a priori neurophysiological evidence. From the final model it is concluded that the initial bilateral symmetrical part of the RP is generated in the posterior walls of the precentral gyrus bilaterally, whereas the later lateralized components originate from the crown of that same gyrus contralaterally. This confirms and extends data from subdural recording, magnetoencephalography (MEG) and EEG.

Adult↗
PubMed1994

A spatio-temporal dipole model of the readiness potential in humans. II. Foot movement.

Readiness potentials (RP) have been recorded in 9 subjects who performed voluntary unilateral plantar flexions with the right or left foot. These show a paradoxical ipsilateral dominance. Spatio-temporal dipole models were obtained for these data, by iterative parameter estimation. The non-uniqueness of the inverse problem leads to several models which describe the data almost equally well, and which all pass orthogonality tests for the individual residuals and source waves. In these dipole models the ipsilateral preponderance is attributed to generators in the contralateral hemisphere, which agrees with results from MEG recording. According to these models the main generators of the RP are in the primary motor cortex, one bilaterally in its posterior wall and the other in the contralateral crown. This agrees with earlier results for finger RPs. However, for foot RPs, it was difficult to distinguish individual sub-components in both the observed scalp potentials and the estimated temporal activation patterns of the dipoles. Some of the presented models include a fronto-central dipole which possibly represents activity of the supplementary motor area. It is concluded that this finding is at best suggestive and needs further investigation.

Adult↗
PubMed1995

Alterations of intrahippocampal cognitive potentials in temporal lobe epilepsy.

During presurgical evaluation event-related potentials were recorded with depth electrodes located longitudinally within the hippocampus in 25 patients suffering from unilateral temporal lobe epilepsy. Rare stimuli in a visual oddball paradigm elicited a pronounced negativity ("NO") in the hippocampal body. Amplitudes were significantly reduced on the side of the primary epileptogenic area. Visual presentations of words in a recognition paradigm evoked an earlier negativity ("ENW") in anterior and a later negativity ("LNW") in posterior hippocampal structures. Both were sensitive for recognition effects and showed reduced amplitudes on the side of the primary epileptogenic area. Relating the differences of left and right hippocampal "NO" and "ENW" amplitudes proved to be a sensitive method for topological diagnosis and allowed a correct lateralization of the primary epileptogenic area in all patients. Amplitudes of the hippocampal ENW, evoked in the dominant hemisphere by first presentations, strongly correlated with the recognition rate, when the primary epileptogenic area was situated in the contralateral temporal lobe. This correlation was reduced by the presence of ipsilateral epileptogenic foci.

Adolescent↗