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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 After they had experienced this contingency for 40 trials, control was withdrawn in that the IS lasted for 5 s during another 40-trial block, irrespective of the actual motor response of the subject.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.

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.

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.

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.

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.

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.

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.

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.

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.

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.