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Biomedical subjects

T Elbert

Publications and source records attributed to T Elbert.

At least 127 records · Page 7Linked to original sources
PubMed1987

The pattern and habituation of the orienting response in man and rats.

Autonomic and central nervous indices of the orienting response (OR) were investigated in awake human subjects and sleeping rats. Ten acoustic stimuli of 60 dB and two stimuli of 80 dB were presented for 10 s each with a constant interstimulus interval of 50 s. Responses were averaged across subjects for each single trial. An exponential fit to scores of each physiological variable was used to compare OR, habituation and dishabituation between samples and variables. An OR to the first stimulus, habituation of response amplitude, and dishabituation in response to the change in stimulus intensity were observed for event-related EEG desynchronization, a negative-positive evoked potential complex in humans and rats, as well as for skin conductance in humans. While heart rate did not show systematic changes across the 60 dB tones in both samples, a deceleration was observed in response to the first 80 dB tone. Results suggest comparable patterns of orienting to acoustic stimuli and habituation of the OR in the awake human and the sleeping rat, suggesting the possibility of OR as a unitary response. Species differed with respect to speed of habituation but not with respect to sensitivity towards stimulus change.

Acoustic Stimulation↗
PubMed1986

Slow brain potentials and the "tunnel effect".

The present study investigated electrocortical concomitants of the "tunnel effect." The tunnel effect refers to the following perceptual phenomenon: if a continuously moving object disappears behind a shield ("enters a tunnel") the observer has the impression that the same object continues to move with the time point of reappearance usually being underestimated. In the present study, an object moved across a tv-screen for 6 s; it either disappeared behind a shield (tunnel condition), disappeared at once (explosion condition), or remained visible until the end of its trajectory (control condition). Subjects had to press a button whenever they believed that the object had arrived at its trajectory's end. The object's flight was accompanied by a continuously rising slow negative shift of the EEG that resembled the contingent negative variation (CNV). Either type of object disappearance produced a positive-going potential that may reflect brain processes associated with memory rehearsal and/or time estimation. A late P300-like positivity was prominent under tunnel conditions only. Response latency was shorter under disappearance than under control conditions. The positive deflection is discussed as sign of amodal brain processing (memory rehearsal and/or time estimation). The P300-like wave elicited by the object's disappearance activates these memory representations. Based on these considerations, an attempt was made to interpret the premature motor responses, which are commonly observed for tunnel conditions but not for other time estimation tasks.

Brain↗
PubMed1986

Patterns of stimulus- and self-induced slow brain potentials--a sign of task-specific preparation.

Does the scalp distribution of slow shifts in human brain potentials depend upon the processing demands? The question was approached applying two different paradigms. In the first study, the anticipation of haptic tasks presented to either of the hands was found to give rise to a contralateral slow negative brain potential (SP). The second study demonstrated that comparable hemisphere-specific patterns can be self-induced by means of biofeedback training. These results suggest that negative SPs (like the CNV) indicate preactivation of those brain-regions that process the expected task.

Biofeedback, Psychology↗
PubMed1985

Removal of ocular artifacts from the EEG--a biophysical approach to the EOG.

The present paper describes the propagation of ocular potentials across the scalp on a biophysical basis. It is concluded that 3 EOG derivations (two for EEG records along the midline) are generally necessary to account for ocular disturbances in the EEG. The inadequacy of many methods suggested for EOG artifact control may be due to the false assumption that just one EOG derivation provides enough information to remove ocular potentials from any EEG recording along the mid(-sagittal) line. A comparison of compensation with one or with two EOG derivations is described for a data set of slow brain potentials. A frequency dependence of the ocular influence cannot be neglected, if fast and slow EOG activities have to be removed. The present considerations should allow a more theoretically based decision of the EOG correction method necessary for a certain data set.

Biophysical Phenomena↗
PubMed1985

Asymmetry of brain potentials related to sensorimotor tasks.

The present study investigates the hemispheric specificity of event-related (ERP) and slow potentials (SP) of the brain during preparation and performance of sensorimotor (haptic) tasks. Tasks were selected which have been assumed to be processed primarily by only one brain hemisphere. ERPs, SPs and spontaneous EEGs were obtained from both hemispheres (C3-C4, P3-P4) and from Fz and Cz in a constant foreperiod (6 s) paradigm. Warning and task stimuli comprised up to four tactile stimuli, applied to index and middle finger of each hand. To maximize lateralized processing, the right-hand task required counting, the left hand task pattern matching. Components of the ERP (N1, P3, SW) and of SPs show task-dependent lateral asymmetry with the larger amplitudes contralateral to the preparing and responding hand. Results confirm hemisphere-specific processing of the tactile tasks but quantification as indicated by ERP amplitudes show considerable activity in both hemispheres. The SP-distribution rather reflects task-specific preparation than general alertness or orienting.

Adult↗
PubMed1985

The perception of Necker cube reversal interacts with the Bereitschaftspotential.

Subjects observed a reversible figure (Necker cube), and were asked to switch a lever about twice a minute. The direction of the lever switch indicated whether a reversal of the Necker cube was just experienced or not experienced. The Bereitschaftspotential (BP, readiness potential) turned out to be smaller in amplitude but earlier in onset prior to the reversal, especially over fronto-central regions. During another condition a tonic background stimulation (achieved by a radio-play) was introduced. Distraction reduced the BP, mainly when no reversal was reported. The results suggest a dependency of pre-movement potentials from non-motoric, psychological variables.

Adult↗
PubMed1984

Operant control of EEG and event-related and slow brain potentials.

Research on operant control of brain potentials is reviewed. From single-unit firing and spontaneous EEG activity to event-related potentials such as sensory and pain evoked potentials, and slow potential shifts, most of the aspects of electrical brain activity have been investigated. Results produced by conditioning of spontaneous EEG oscillations (alpha and theta) dampened the early enthusiasm: e.g., no increase above baseline levels could be achieved and no reliable behavioral effects became manifest. Evidence accumulates, however, that operant conditioning of the sensorimotor rhythm (12-15 Hz) may lead to successful self-regulation and that epileptic patients may profit from the training. First steps in the conditioning of brainstem, as well as pain evoked potentials suggest that self-regulation of EPs can be achieved by adequate biofeedback procedures. If some of the observed behavioral effects prove to be stable, the therapeutic usefulness seems to be within reach. A comparable progress has been achieved for the operant control of slow potentials (DC-shifts across seconds). Biofeedback procedures have been used successfully as a scientific tool to achieve systematic variations on a psychological level and to record psychological covariations. This method may provide insights into the behavioral meaning of electrical brain activity.

Biofeedback, Psychology↗
PubMed1983

Evaluation of contingencies and conditional probabilities. A psychophysiological approach to anhedonia.

Slow brain potentials, evoked potentials and autonomic responses were investigated in anhedonic subjects and controls. The distribution of physical anhedonia (PA) scores from different samples (students, soldiers, schizophrenics, depressives) is compared. Within a S1-S2 reaction time paradigm, an additional, S2-similar stimulus was introduced during the anticipation interval in 50% of trials (pseudorandom). Subjects had to press the button only to the S2. The additional stimulus (AS) elicits a distinct positive deflection. Anhedonics show larger pre-AS negativity and less reduction in negativity after the S2 (PINV) than controls. The slow wave to S1 as well as the pre-AS negativity vary with the conditional probability of the AS, but to a lesser extent in anhedonics. Anhedonics provide more preparatory negativity prior to and following ambiguous or difficult discrimination tasks, but at the frontal site. Results may suggest impaired contingency evaluation in anhedonic subjects.

Adolescent↗
PubMed1983

Distractability under the influence of an ACTH 4-9 derivative.

Event-related brain potentials, autonomic responses, and response latency under distraction conditions served to investigate the effects of an ACTH 4-9 derivative (ORG 2766) on attention. Male volunteers (45) received either 40 mg ORG 2766 or placebo in a double-blind setting. Two-stimulus trials with acoustic warning signal (S1) and acoustic S2 which had to be interrupted by immediate button press, preceded trials with distraction during the warning interval in 50% of the trials. A final period without distraction served to test for rebound effects. A reduction in early CNV was found in placebo subjects under distraction, while subjects under ORG 2766 showed no reduced early negativity, but increased late negativity under this condition. Peptide subjects differed from controls in evoked potential components, showing enhanced N1 and P3 amplitudes. Activity in the alpha band was elevated. Postexperimental systolic blood pressure was raised by 15 mm Hg under ORG 2766. Results are in agreement with previous findings and suggest ORG 2766 effects on distraction resistance and attention fixation.

Adrenocorticotropic Hormone↗
PubMed1982

Slow brain potentials after withdrawal of control.

The present experiment was designed to replicate and extend the previous finding of an increased postimperative negative slow brain potential shift (PINV) in healthy subjects following an unexpected change from the condition of control over an aversive imperative stimulus to that of loss of control. Two groups of 16 male students each participated in a constant-foreperiod reaction time paradigm with two warning stimuli (WS), each of 6 s duration, followed by two imperative stimuli (IS) of either aversive (loud noise) or neutral (soft tone) quality. The experimental subjects could terminate each IS by pressing a microswitch within 300 ms of IS-onset. After they had experienced this contingency for 40 trials, control was withdrawn in that the IS lasted for 5 s during another 40-trial block, irrespective of the actual motor response of the subject. The yoked control subjects received the same stimuli and performed the same motor response as the experimental subjects, but experienced no contingency between response and IS-termination. EEGs were recorded monopolarly from Fz, Cz, and Pz. In response to the unexpectedly uncontrollable aversive IS, the experimental subjects showed a pronounced PINV over frontal areas, while no comparable PINV developed in yoked controls. Experimental subjects showed no PINV during the first trial block (control conditions), and in response to the neutral uncontrollable IS. Statistical analyses of principle components documented that the PINV can be considered an independent endogenous component.

Avoidance Learning↗
PubMed1982

EEG and slow brain potentials during anticipation and control of painful stimulation.

Cerebral responses in anticipation of painful stimulation and while coping with it were investigated in a "fakir" and 12 male volunteers. Experiment 1 consisted of 3 periods of 40 trials each. During period 1, subjects heart one of two acoustic warning stimuli of 6 sec duration signalling that either an aversive noise or a neutral tone would be presented at S1 offset. During period 2, subjects were asked to use any technique for coping with pain that they had ever found to be successful. During period 3, the neutral S2 was presented simultaneously with a weak electric shock and the aversive noise was presented simultaneously with a strong, painful shock, again under pain copying instructions. EEG activity within the theta band increased in anticipation of aversive events. Theta peak was most prominent in the fakir's EEG. A negative slow potential shift during the S1-82 interval was generally more pronounced in anticipation of the aversive events that the neutral ones, even though no overt motor response was required. Negativity tended to increase across the three periods, opposite to the usually observed diminution. In Experiment 2, all subjects self-administered 21 strong shock-noise presentations. The fakir again showed more theta power and more pronounced EEG negativity after stimulus delivery compared with control subjects. Contrary to the controls, self-administration of shocks evoked a larger skin conductance response in the fakir than warned external application.

Adult↗
PubMed1981

EEG and slow cortical potentials in anticipation of mental tasks with different hemispheric involvement.

Mental arithmetic is supposed to be processed by the left hemisphere, while pattern matching has been considered to be processed by the right hemisphere. These different mental tasks were presented to 16 right-handed male subjects. As a variable task difficulty was varied for the two task categories. The task presentations were preceded by 6 sec warning stimuli which indicated the level of difficulty of the task. EEG and slow cortical potentials (SCPs) were recorded from temporal and precentral leads of both hemispheres. The reference was noncephalic. During the anticipation interval beta-activity was enhanced above the hemisphere primarily involved in the particular task. SCPs failed to show a comparable clear pattern. A late negative component showed task-dependent asymmetries prior to easy tasks, but not prior to difficult tasks.

Adolescent↗
PubMed1981

Principal component analysis of slow brain potentials during six second anticipation intervals.

The comparison of principal component analyses between seven experimental studies demonstrates a remarkable similarity of the extracted components. Slow scalp-recorded potentials of the brain (SPs) during a constant 6 sec foreperiod can be described by an early frontal, and a late preparatory component. Furthermore, an additional intermediate component may be retained by the PCA. This component seems to reduce the between-subject variance and often describes processes dependent on stimulus repetition. There is evidence favoring the varimaxed solution of the PCA for the parametrization of most of the experimental data.

Biofeedback, Psychology↗