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Biomedical subjects

W Lutzenberger

Publications and source records attributed to W Lutzenberger.

At least 19 recordsLinked to original sources
PubMed1995

Spectral responses in the gamma-band: physiological signs of higher cognitive processes?

It has recently been proposed that brain responses in the gamma-range (> 20 Hz) include information about specific cognitive processes in the human brain. Empirical data substantiating this assumption come from EEG and MEG recordings during visual and language processing. For example, 30 Hz activity has been found to be stronger during processing of words than during processing of meaningless but pronounceable pseudo-words. However, it has been reported that power changes in the gamma-band are sometimes artefacts of changes taking place in other frequencies, such as the alpha-band. In this study, we investigated power changes in frequency bands outside the gamma-range and found no evidence that such changes are related to the dynamics in gamma-power distinguishing between words and pseudowords. These results are consistent with the view that gamma-band responses are an indicator of lexical processing and other cognitive processes related to binding of stimulus features into a whole (Gestalt), as proposed by Singer.

Acoustic Stimulation↗
PubMed1995

Do schizophrenics not differentiate between perception and imagination? an EEG study using dimensional analysis.

The electroencephalograms (EEGs) of 18 chronic schizophrenic patients and 16 controls were compared during three experimental conditions: simple mental arithmetic, the perception of a moving double pendulum, and the imagination of it. An elevated dimensional complexity of the EEG of schizophrenic patients during perception as compared to normals and a failure to increase dimensional complexity during mental imagery was found. No differences were found during mental arithmetic. It is concluded that the brains of schizophrenics operate during perception in a functional state that is characterised by increased and apparently unnecessary complexity.

Adult↗
PubMed1995

Evoked potentials distinguish between nouns and verbs.

Electrocortical correlates of the processing of nouns and verbs were recorded in 32 healthy individuals performing lexical decisions. Analyses of EEG data recorded through 29 channels revealed different topographies of cortical activity evoked by nouns and verbs. Differences were most pronounced at recording sites over the frontal lobes. The stronger motor associations elicited by verbs as measured pre-experimentally seem to be responsible for the topographical differences of event related brain potentials to verbs and nouns. In agreement with recent evidence from brain-damaged subjects, these results provide evidence that (1) nouns and verbs have distinct neural generators and that (2) these generators involve areas outside the classical language regions of the brain.

Cerebral Cortex↗
PubMed1995

Motor programming in both hemispheres: an EEG study of the human brain.

Differential hemispheric involvement in controlling simple and complex motor movements was investigated in humans using EEG spectral responses. Analysis of spectral power in the alpha band revealed the following. While during a simple motor task (tapping) signs of unilateral cortical activation were present, more complex sequential motor behaviour (Luria finger apposition task) led to symmetrical bihemispheric activation. It appears that unilateral cortical processing is present in the normal brain when very simple computations are performed. Bilateral hemispheric activity and interhemispheric interaction may be general features of more complex information processing in the cortex.

Brain↗
PubMed1995

Visual stimulation alters local 40-Hz responses in humans: an EEG-study.

Irregular changing visual patterns and coherently moving bars were presented either in the upper or lower half of the visual field of 12 human subjects. EEG responses recorded over the occipital lobe showed an increase of 40 Hz spectral power when a regular pattern of moving bars appeared. This enhancement of 40-Hz activity varied as a function of visual field presentation. Coherent stimuli in the upper visual field elicited 40-Hz enhancement at lower occipital electrodes, while coherent stimulation in the lower visual field elicited 40-Hz enhancement at upper occipital electrodes. These results evidence that neuronal 40-Hz responses are a correlate of perception of coherent visual patterns in humans. Area-specific 40-Hz responses related to visual perception can be picked up in the EEG.

Adult↗
PubMed1995

Fractal dimension of electroencephalographic time series and underlying brain processes.

Fractal dimension has been proposed as a useful measure for the characterization of electrophysiological time series. This paper investigates what the pointwise dimension of electroencephalographic (EEG) time series can reveal about underlying neuronal generators. The following theoretical assumptions concerning brain function were made (i) within the cortex, strongly coupled neural assemblies exist which oscillate at certain frequencies when they are active, (ii) several such assemblies can oscillate at a time, and (iii) activity flow between assemblies is minimal. If these assumptions are made, cortical activity can be considered as the weighted sum of a finite number of oscillations (plus noise). It is shown that the correlation dimension of finite time series generated by multiple oscillators increases monotonically with the number of oscillators. Furthermore, it is shown that a reliable estimate of the pointwise dimension of the raw EEG signal can be calculated from a time series as short as a few seconds. These results indicate that (i) The pointwise dimension of the EEG allows conclusions regarding the number of independently oscillating networks in the cortex, and (ii) a reliable estimate of the pointwise dimension of the EEG is possible on the basis of short raw signals.

Brain↗
PubMed1995

Electrocortical distinction of vocabulary types.

Psycholinguistic theories propose that words of the 2 major vocabulary classes, content (open-class) and function (closed-class) words, are computationally distinct and have different neuronal generators. This predicts distinct EEG patterns elicited by words of these 2 classes. To test this prediction, content and function words, together with matched pseudowords, were presented in a lexical decision task (where subjects had to decide whether stimuli were meaningful words or not). Evoked potentials were recorded from 17 electrodes 12 of which were located in close vicinity of the perisylvian cortices. Already 160 msec post stimulus onset, substantial differences in activity patterns distinguish the 2 vocabulary classes. A hemisphere by word class interaction revealed interhemispheric differences for function words but not for content words. Potentials evoked by function words were more negative over the left hemisphere compared to the right. These results evidence that brain mechanisms underlying function and content word processing are different. The following explanation of the data is proposed: content words correspond to neuronal assemblies equally distributed over both hemispheres, while assemblies corresponding to function words are strongly lateralized to the left hemisphere and primarily located in the perisylvian region.

Adult↗
PubMed1994

Words and pseudowords elicit distinct patterns of 30-Hz EEG responses in humans.

Meaningful words, such as moon, and physically similar but meaningless pseudowords, such as noom, were presented visually in a lexical decision task. The EEG was recorded from 17 scalp electrodes. Significant differences between both stimulus classes were observed in evoked spectral responses of the 'gamma-band' approximately 30 Hz. A hemisphere by wordness interaction demonstrated that 30-Hz spectral power over the left hemisphere was reduced after pseudowords only. These results indicate that gamma-band responses reflect the different cognitive processes induced by words and pseudowords. A possible explanation is the following. Synchronous activation of large cortical cell assemblies takes place after word presentation but not after presentation of pseudowords.

Brain↗
PubMed1994

Slow cortical potential biofeedback and the startle reflex.

The negativity of slow cortical potentials (SCP) of the surface EEG is a measure of brain excitability, correlating with motor and cognitive preparation. Self-control of SCP positivity has been shown to reduce seizure activity. Following SCP biofeedback from a central EEG electrode position, subjects gained bidirectional control over their SCP. The current study used a modified feedback methodology, and found a positive relationship between negativity and magnitude of EMG startle response (a measure of cortical and subcortical arousal, particularly aversive response disposition). Greater success in SCP differentiation was associated with self-report of less relaxation during negativity training.

Adult↗
PubMed1994

Positive shifts of event-related potentials: a state of cortical disfacilitation as reflected by the startle reflex probe.

Cortical positivity as measured by slow event-related potentials is assumed to represent a decreased excitability of cortical networks and suppression of their behavioral-cognitive output. The blink reflex probe is a commonly used defensive electromyographic response whose amplitude was shown to be modulated by emotional and attentional orientation. It was used here as an indicator of cortico-subcortical excitation. In study 1, 33 healthy subjects took part in a continuous performance test (CPT). Event-related potentials were recorded from 15 standard scalp locations. Acoustic startling noise bursts were delivered during conditions that required either performance of prepared motor responses (Go), inhibition of prepared motor responses (NoGo), or had no motor significance (Irrelevant condition). During the NoGo condition, EEG surface potentials showed a widespread P300-like positivity with a central maximum. Startle responses were inhibited during the NoGo condition as compared to the Irrelevant condition. In study 2 (21 subjects) the same format was used, except that the startle reflex was elicited visually. Startle reflexes again showed smaller magnitude during the NoGo condition, which evoked larger positivity at central sites in comparison to the Irrelevant condition. The relationship between positivity in the EEG and inhibited startle responses is in line with the hypothesis that positive EEG shifts reflect a state of cortical disfacilitation.

Acoustic Stimulation↗
PubMed1994

Mapping P300 waves onto inhibition: Go/No-Go discrimination.

Subjects viewed letters presented at 2 sec intervals and prepared a fast button press whenever an "O" appeared. If the next letter was an "X" the button press was executed (Go signal), but if the letter was a non-X character (T, H, Z) suppression of the response was required (No-Go cue). No-Go signals elicited a P300-like wave that was larger at central and frontal scalp sites contralateral to the prepared movement, compared to P300s elicited by Go cues which were symmetric about the sagittal midline and dominant at parietal sites. Subtraction of preparatory CNVs from the No-Go P300 did not remove differences in scalp topography, or reduce the amplitude of the No-Go P300 to that seen following control letters that required perceptual identification but did not call for suppression of prepared motor responses. Principal components analysis identified a middle positive wave following X-alone control stimuli whose topography resembled the No-Go P300. These findings suggest that the source of augmented No-Go P300s is a generator involved with sensorimotor inhibition. We discuss the mechanism of P300 waves and evidence linking these waves with inhibition in other task arrangements.

Adult↗
PubMed1994

Neurophysiological differences between perception and imagery.

The present study was designed to examine brain activity underlying mental imagery is conceptualized as behavior guided by internal representation only, the activity of the prefrontal lobes was assumed to be a measure of differentiation of imagery from perception. Twenty-one subjects were requested to observe and imagine a swinging pendulum and to touch and imagine a coshball in separate trials. The EEG was recorded from 15 standard electrode sites and analyzed with (1) traditional alpha power and (2) an estimation of dimensional complexity (a measure derived from nonlinear dynamics). Both EEG measures revealed expected object-related differences during perception as well as during imagery. The visual pendulum showed relative to the tactile coshball increased dimensional complexity and less alpha power at parietal and frontal sites. However, only the EEG dimension supported the main hypothesis: Imagery resulted in increased prefrontal dimensional complexity in comparison to perception independent of the modality of the image. In contrast, for alpha power the difference between imagery and perception was due to stimulus modality.

Adolescent↗
PubMed1994

Brain potentials during mental arithmetic: effects of extensive practice and problem difficulty.

Recent behavioral investigations indicate that the processes underlying mental arithmetic change systematically with practice from deliberate, conscious calculation to automatic, direct retrieval of answers from memory [Bourne, L.E.Jr. and Rickard, T.C., Mental calculation: The development of a cognitive skill, Paper presented at the Interamerican Congress of Psychology, San Jose, Costa Rica, 1991: Psychol. Rev., 95 (1988) 492-527]. Results reviewed by Moscovitch and Winocur [In: The handbook of aging and cognition, Erlbaum, Hillsdale, NJ, 1992, pp. 315-372] suggest that consciously controlled processes are more dependent on frontal lobe function than are automatic processes. It is appropriate, therefore to determine whether transitions in the locus of primary brain activity occur with practice on mental calculation. In this experiment, we examine the relationship between characteristics of event-related brain potentials (ERPs) and mental arithmetic. Single-digit mental multiplication problems varying in difficulty (problem size) were used, and subjects were trained on these problems for four sessions. Problem-size and practice effects were reliably found in behavioral measures (RT). The ERP was characterized by a pronounced late positivity after task presentation followed by a slow wave, and a negativity during response indication. These components responded differentially to the practice and problem-size manipulations. Practice mainly affected topography of the amplitude of positivity and offset latency of slow wave, and problem-size mainly offset latency of slow wave and pre-response negativity. Fronto-central positivity diminished from session to session, and the focus of positivity centered finally at centro-parietal regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Memory performance and area-specific self-regulation of slow cortical potentials: dual-task interference.

We examined the effect of area-specific feedback for slow potentials on sensorimotor and memory performance under single and dual-task conditions. Subjects observed a memory set for 400 ms and then determined 5 s later whether a target letter had been contained in the original presentation (Sternberg task). After one session of Sternberg-only training, feedback training was added for production of negative and positive slow potentials area-specifically at Fz, Cz or Pz during the 5-s interval separating the memory set and target probes. Addition of the feedback task resulted in an increase in Sternberg response latency and errors which was followed by gradual recovery over five dual-task sessions (recovery not complete for the error measure). Subjects successfully regulated their slow potentials, but only in an area-nonspecific fashion, even though area-specific control was observed in an earlier study under a feedback-only condition. Sternberg performance did not depend on whether slow potential negativity or positivity was produced. These findings indicate that competition between tasks was a more important determinant of performance than was modulation of dendritic polarization by feedback-induced slow potentials.

Adult↗
PubMed1993

Cortical self-regulation in patients with epilepsies.

The present study aimed at investigating to what extent the regulation of excitability in cortical networks, as indicated by surface-negative slow cortical potentials (SCPs), is impaired in epileptic patients and to what extent training of SCP self-regulation by means of biofeedback and instrumental learning procedures might affect seizure frequency. Twenty-five patients suffering from drug-refractory epilepsies (complex focal, grand mal, and absence type of seizures) participated in 28 1-h sessions of feedback and instrumental conditioning of their SCPs. Subjects' EEGs were obtained from the vertex. Depending on discriminative stimuli DC shifts towards increased or suppressed negativity relative to the pre-trial baseline were demonstrated by on-line visual feedback during intervals of 8 s each; each session comprised 110 trials. While performance on the SCP self-regulation task was initially below normal (as compared to healthy subjects), significant increases in SCP control were achieved by the patients across the 28 training sessions. In 18 patients at least 1-year follow-up data are available. Changes in seizure frequency were related to transfer of SCP control with six of the patients becoming seizure-free. Age affected the ability to acquire SCP control and its impact on seizure frequency.

Adolescent↗
PubMed1993

Classical conditioning after cerebellar lesions in humans.

We explored classical conditioning in human subjects who had lesions in their cerebellar circuitry. Seven patients with damage to cerebellar structures and matched control subjects underwent simple delay tone-airpuff conditioning. Eyelid conditioned response (CR) acquisition was severely disrupted in the patient group, whereas autonomic CRs and slow cortical potentials developing between conditioned stimulus (CS) and the unconditioned stimulus (UCS) were unaffected. Results are consistent with animal studies and earlier case reports indicating that intact cerebellar structures are necessary for the acquisition of classically conditioned motor responses.

Adult↗
PubMed1993

Behavioural treatment of slow cortical potentials in intractable epilepsy: neuropsychological predictors of outcome.

The study aimed to explore the predictive value of neuropsychological tests within the context of acquisition of slow cortical potential (SCP) self-control, a technique which has beneficial effects on seizure frequency in epilepsy. Patients with epilepsy who successfully achieved SCP control had longer digit or block-tapping spans than less successful patients. Patients who showed a better learning rate across training also displayed better verbal memory and learning abilities. Seizure reduction was related to block-tapping spans only. The results indicate that measures of attention, as indicated by digit spans or block-tapping spans, offer some predictive value for acquisition of SCP control and treatment outcome, whilst measures of visuospatial or frontal lobe function are unrelated to SCP acquisition and seizure reduction.

Adolescent↗