Search PubMed⌕ Search

Biomedical subjects

T Elbert

Publications and source records attributed to T Elbert.

At least 145 records · Page 8Linked to original sources
PubMed1981

The influence of low-level transcortical DC-currents on response speed in humans.

Low-level direct currents (DC) are thought to polarize brain tissue and to affect brain processes. The present experiments investigated the effects of low-level transcortical DC-currents on response speed and physiological variables in humans. The DC-currents were applied during the warning interval within a constant foreperiod reaction time paradigm. Currents of less than 0.3 mA were applied between a vertex electrode and a noncephalic reference. The polarity of the electrical source varied randomly across trials within subjects. The first two studies showed that subjects respond fastest when the positive pole is applied to the vertex. Under the same conditions higher skin conductance responses were observed as compared to vertex negative conditions. The dynamics of the observed responses suggest that the brain "learns" to respond differentially to the different current polarities. This was confirmed by the third study, which documented different conditioned electroencephalic responses subsequent to current application.

Cerebral Cortex↗
PubMed1981

The influence of low-level, event-related DC-currents during time estimation in humans.

Two experiments were designed to investigate further the influence of low-level transcephalic DC currents on human reaction time and time perception. Thirty-two subjects participated in the experiments, with the second one a replication of the first. During a first trial series, subjects responded to the offset of a 6 second tone. Simultaneous to tone presentation a current was applied between vertex and collar bone electrodes. Current polarity varied randomly across trials. During a second trial series, subjects interrupted tone and current when they estimated a time interval of same length as the previously experienced had elapsed. In both studies subjects interrupted the tone/current after a shorter interval when the negative pole was applied as compared to vertex-positive trials. Results suggest that a vertex-negative external current suppresses an internally required state, whereas an external positive current supports internal SP-generation. The brain may tend to terminate the former state earlier than the latter.

Acoustic Stimulation↗
PubMed1980

Biofeedback of slow cortical potentials. I.

An experiment was performed to investigate the self-regulation of slow cortical potentials (SCP) found in a previous study (Elbert et al. 1979). Seventeen subjects received continuous visual feedback of their actual cortical shift perceptible as a rocket moving across a TV-screen during intervals of 6 sec; subjects had to direct the rocket into one of two goals representing more or less cortical negativity, depending on the pitch of two signal tones. Within two identical experimental sessions feedback trials alternated with test trials without feedback. Highly significant differences of SCP between the two required polarities were demonstrated. The most pronounced differences were observed during test trials without feedback of the second session in which a positive shift below baseline level occurred when positivity (or less negativity) was required.

Adult↗
PubMed1980

Biofeedback of slow cortical potentials. II. Analysis of single event-related slow potentials by time series analysis.

A single trial analysis of slow cortical potentials treating the EEG as a time series was developed. The method was applied to data resulting from an experiment on self-regulation of slow cortical potentials (SCP). Parametric models of the EEG were developed on the basis of autoregressive filter models and a two-component model of SCP (during 6 sec intervals), taking into account ocular influences as a further parameter. Results from different models were compared with each other and with results of averaging SCP data. For the present data time series analysis and traditional analysis provided qualitatively equal results, but fewer trials were necessary for analysis in the single trial approach and more detailed structures of the data became evident. If the EEG was filtered above 5 Hz it could be described by an autoregressive filter model of low order. Ocular influences were estimated as too small in a non-filtered EEG compared to the filtered EEG.

Biofeedback, Psychology↗
PubMedDate not supplied

Degradation of a radiolabeled juvenile hormone analog using two insect species.

A synthetic insect juvenile hormone analog (a juvenoid), ethyl N-[2-[4-[[2,2-(ethylenedioxy)cyclohexyl]methyl]phenox]ethyl]carbam ate, which has displayed high biological activity against different insect species and high stability under field conditions, was selected as a biologically active model compound for a study of a juvenile hormone analog degradation. The biologically active compound itself and its three diversely radiolabeled derivatives were applied to the flesh fly (Sarcophaga bullata) or the tsetse fly (Glossina palpalis), respectively. Monitoring of a fate of the applied juvenile hormone analog was carried out using a detection method of the radioactivity microdistribution within the whole insect body in combination with a radio high performance liquid chromatography (radio-HPLC), both of whole-body extracts made in different, but in advance scheduled, time intervals, and of extracts of insect excreta accumulated over an eight-day experiment.

Animals↗
PubMedDate not supplied

Changes of chaoticness in spontaneous EEG/MEG.

Depending on the task being investigated in EEG/MEG experiments, the corresponding signal is more or less ordered. The question still open is how can one detect the changes of this order while the tasks performed by the brain vary continuously. By applying a static measurement of the fractal dimension or Lyapunov exponent, different brain states could be characterized. However, transitions between different states may not be detected, especially if the moments of transitions are not strictly defined. Here we show how the dynamical measure based on the largest local Lyapunov exponent can be applied for the detection of the changes of the chaoticity of the brain processes measured in EEG and MEG experiments. In this article, we demonstrate an algorithm for computation of chaoticity that is especially useful for nonstationary signals. Moreover, we introduce the idea that chaoticity is able to detect, locally in time, critical jumps (phase-transition-like phenomena) in the human brain, as well as the information flow through the cortex.

Algorithms↗
PubMedDate not supplied

Conditional tonic stimulus control of nonspecific arousal.

Subjects performed a reaction time (RT) task in the presence of colored indirect lighting which had previously been associated with either sporadic electric shock (Unsafe context) or no shock (Safe context). Autonomic and cortical processes were influenced by the visual context in two ways. Nonspecific arousal was elevated in the Unsafe context as compared with the Safe context (larger SCR and more accelerative HR change elicited by the RT warning stimulus, and retarded habituation of the middle component of the slow cortical potential during the warning stimulus). In addition, information processing may have been impaired in the Unsafe as compared to the Safe context, since the earliest component of the SCR and the N100 component of the auditory evoked potential were both reduced. Higher frequency of unelicited SCR was observed following changes from a Safe to an Unsafe context than with reverse changes, during the association of these contexts with shock, but this was the only evidence of direct tonic conditioning. In general, the results demonstrate the degree to which psychophysiological processes may be influenced by tonic environmental conditions.

Adolescent↗
PubMedDate not supplied

Area-specific self-regulation of slow cortical potentials on the sagittal midline and its effects on behavior.

Exteroceptive feedback was given for negative and positive shifts in slow potentials (SPs) recorded from Fz, Cz, or Pz (between groups design). Slow potentials at the feedback site were referred to adjacent scalp and non-cephalic electrodes, so as to confine SP shifts to the feedback location. Area-specific regulation of SPs was obtained at each midsagittal site after 3 days of feedback training. Subjects reported sensorimotor and emotional arousal when negative SP shifts were trained frontally, but not when negative shifts were trained parietally (cognitive/attentional strategies reported after parietal feedback). Area-specific regulation of SPs was subsequently abolished when behavioral tasks were added to further probe frontal/parietal differences (dual-task procedure). These findings indicate that area-specific self-regulation of SPs is possible on the sagittal midline, and that self-regulated parietal SPs (in contrast to frontal ones) arise from non-motoric generators. The source of SP self-regulation was more readily probed by verbal reports of feedback strategy than by study of dual-task relations, because feedback control was disrupted by the dual-task requirement.

Adult↗
PubMedDate not supplied

Relationship of transient and steady-state auditory evoked fields.

Transient and steady-state auditory evoked fields (AEFs) to brief tone pips were recorded over the left hemisphere at 7 different stimulus rates (0.125-39 Hz) using a 37-channel biomagnetometer. Previous observations of transient auditory gamma band response (GBR) activity were replicated. Similar rate characteristics and equivalent dipole locations supported the suggestion that the steady-state response (SSR) at about 40 Hz represents the summation of successive overlapping (10 Hz) middle latency responses (MLRs). On the other hand, differences in equivalent dipole locations and habituation effects suggest that the magnetically recorded GBR is a separate phenomenon which occurs primarily at low stimulus rates and is unrelated to either the magnetically recorded MRL or SSR.

Acoustic Stimulation↗
PubMedDate not supplied

Vasopressin does not enhance memory processes: a study in human twins.

Behavioral effects of lysin-vasopressin (LVP) were investigated applying two paradigms from human experimental psychology. The first task was designed to simulate amnesic symptoms in normals. The second task addressed the emotional value of the items to be processed. Additionally, EEG recordings were used as indicators of the central nervous system effectiveness of LVP. Blood pressure and heart rate measured peripheral arousal. The co-twin control method was employed to increase experimental power. Contrary to the prediction of the vasopressin memory hypothesis none of the specific memory parameters was improved by LVP treatment. Changes in the electrical activity of the brain, but not in blood pressure and heart rate indicated central nervous system actions of LVP. However, interpretation of LVP effects in terms of memory processing seems not to be justified.

Adolescent↗
PubMedDate not supplied

Biofeedback produced slow brain potentials and task performance.

Twenty subjects learned to control slow potential (SP) shifts of the brain by means of a biofeedback procedure. Depending upon the pitch of a signal tone, negative SP shifts had to be increased or reduced during intervals of 6 sec each. Visual feedback of the actual SP shift was given. Blocks of training trials alternated with blocks of test trials without any feedback of the SPs. At the end of every test trial a simple arithmetic problem had to be solved by the subjects. Subjects performed the computation in a shorter time interval if an increased negativity preceded task onset as compared to slower response times during suppression of negativity. Results suggest that cortical negativity reflects unspecific preparation for cerebral performance.

Attention↗
PubMedDate not supplied

Psychophysiology of arterial baroreceptors and the etiology of hypertension.

Arterial baroreceptors are sensitive to blood pressure dependent blood vessel dilation. They play a key role in the short term regulation of blood pressure. Their impact on psychological and psychophysiological aspects is of increasing interest. The review focuses on experimental techniques for the controlled baroreceptor manipulation. Results from the application of these techniques show that baroreceptor activation influences the cardiovascular system as well as central nervous functioning: Behavioral and electrophysiological measures of arousal, low level reflexes and pain responses are modulated through baroreceptor manipulation. The observation of an overall dampening ('barbiturate like') effect of baroreceptor activity led Dworkin et al. formulate the theory of learned hypertension: Subjects might experience blood pressure dependent baroreceptor activation as stress and pain relieving. High blood pressure periods become negatively reinforced. Phasic high blood pressure might develop as a coping strategy. Data from a longitudinal human study supporting this theory are reported.

Arousal↗