Showing papers by "Werner Lutzenberger published in 1992"

The scalp distribution of the fractal dimension of the EEG and its variation with mental tasks

Abstract: The insights gained by the concept of deterministic chaos for the EEG is that this seemingly disordered process may be governed by relatively few simple laws which could be determined. One of the quantitative measures of a complex dynamical system is that of its dimension. The term ‘dimension’ refers to the ability of a space to contain a set of points. We estimated the correlational dimension of the EEG and compared the outcome to traditional Fourier analyses. In addition, we tested the hypothesis that the EEG can be described as filtered noise. Data from 15 electrode sites and 31 subjects are reported in the present study. We have utilized a variety of tasks that cut across sensory modalities including touch, vision, and imagery which reflect neuropsychological processes that differentially engage areas of the cortex in the first part of the study. In the second part, the differences between the perception of an object and the imagination of the same object were evaluated. The outcome shows variations between scalp sites for all measures and also variations between tasks in terms of dimensionality of the EEG. The hypothesis of a higher dimensionality ("complexity") of imagery compared to actual perceptual processing was confirmed. A statistical comparison between the maps generated by means of the various measures shows that different informations are extracted when using the different measures. There is also statistical evidence that the EEG cannot completely be described by the model of filtered noise.

Symptom-specific psychophysiological responses in chronic pain patients.

Abstract: Symptom-specific psychophysiological responding was assessed in 20 chronic back pain patients, 20 patients suffering from temporomandibular pain and dysfunction, and 20 matched healthy controls. Surface EMG from the lower and upper back, the masseter, and the biceps muscles, and heart rate and skin conductance level were continuously recorded during adaptation, resting baseline, and stressful and neutral imagery phases. Univariate and multivariate analyses of variance were performed on raw data as well as data corrected for autocorrelation. The results showed significantly higher EMG reactivity which was lateralized to the left side at the patients' site of pain but not distal sites. This hyperreactivity was observed only during stressful imagery. The healthy controls displayed a significantly higher response in heart rate, but skin conductance level was not significantly different. The results are interpreted as indicative of idiosyncratic muscular response patterns to personally relevant situations at the site of pain in patients suffering from chronic muscular pain.

Self-regulation of slow cortical potentials in psychiatric patients: Schizophrenia

Abstract: Slow cortical potentials (SCPs) are considered to reflect the regulation of attention resources and cortical excitability in cortical neuronal networks. Impaired attentional functioning, as found in patients with schizophrenic disorders, may covary with impaired SCP regulation. This hypothesis was tested using a self-regulation paradigm. Twelve medicated male schizophrenic inpatients and 12 healthy male controls received continuous feedback of their SCPs, during intervals of 8 s each, by means of a visual stimulus (a stylized rocket) moving horizontally across a TV screen. The position of the feedback stimulus was a linear function of the integrated SCP at each point in time during the feedback interval. Subjects were required to increase or reduce negative SCPs (referred to pretrial baseline) depending on the presentation of a discriminative stimulus. The correct response was indicated by the amount of forward movement of the feedback stimulus and by monetary rewards. Schizophrenics participated in 20 sessions (each comprising 110 trials), while controls participated in 5 sessions. Compared with the healthy controls, schizophrenics showed no significant differentiation between negativity increase and negativity suppression during the first sessions. However, in the last 3 sessions, patients achieved differentiation similar to controls, demonstrating the acquisition of SCP control after extensive training.

PRES: the controlled noninvasive stimulation of the carotid baroreceptors in humans.

Abstract: To study physiological and psychological effects of baroreceptor activity, the cervical neck cuff technique has been frequently used to stimulate the carotid baroreceptors mechanically. Using this technique, no satisfying control conditions to date have been available. Because the carotid stretch receptors are sensitive not only to the pressure level, but also to the rate of change, it is possible to manipulate the receptor firing through changes in carotid pulse amplitude. The device described here relies on the application of short changes in cuff pressure tied to different phases within the cardiac cycle (phase related external suction (PRES)). A brief external suction during systole has potent stimulatory effects on baroreceptors whereas the application of the very same pressure pulse during diastole inhibits the firing burst associated with the pulse wave. To allow an ongoing period of stimulation, a sequence of alternating negative/positive pressure pulses is applied. In the stimulation condition, the R-wave of the electrocardiogram triggers a negative pulse which is followed by a positive one during diastole. In the control condition this relationship is reversed. Two experiments are reported confirming different baroreceptor effects of the two conditions. PRES allows for blind or double-blind experiments to investigate effects of baroreceptor activity on physiology and behavior.

Self-regulation of slow cortical potentials in psychiatric patients: Depression

Abstract: Findings on depressive patients indicate that depressives have electrophysiological characteristics similar to those of schizophrenics, in that they exhibit reduced Contingent Negative Variation (CNV) amplitudes and more distinct Postimperative Negative Variations (PINVs) than normal controls. In a biofeedback experiment, 8 medicated male inpatients with the DSM III-R diagnosis of “Bipolar Disorder, Depressive,” and “Major Depression” demonstrated no impairment in the self-regulation of Slow Cortical Potentials (SCP) in comparison to schizophrenics in terms of increasing and suppressing negativity. Continuous visual SCP feedback is presented to the patient as a horizontally moving rocket in a video game format. The direction changes of the rocket represented SCP changes at each point in time, recorded by the central EEG (based on the pretrial baseline). Depressives demonstrated SCP self-regulation across 20 sessions, although with many between-and-within variations. The 8 male controls were unable to regulate their SCPs across 5 sessions. This result contradicts other findings of our laboratory on normal controls. Motivational factors and insufficient operant reinforcement (financial reward) may have facilitated this effect.

Modulation of slow cortical potentials by instrumentally learned blood pressure responses.

Abstract: We assessed whether instrumentally-learned pressor responses inhibit electrocortical activity, as predicted by learning theories of idiopathic hypertension. Subjects received beat-by-beat feedback for increases and decreases in mean arterial pressure measured from the finger (Penaz method). Slow potentials were recorded from the midsagittal line during the final training session. Also recorded at this time were heart rate, eye movements, respiration, and post-session verbal reports of the subject's control strategies. Thirteen of 14 subjects differentiated blood pressure increases and decreases at p less than .05 or better during the final session (within-subject discriminative operant procedure). Slow potentials were less negative on blood pressure increase compared to decrease trials at all midsagittal sites (p less than .02), indicating relative cortical inhibition by pressor responses. This effect occurred even though subjects reported tensing of muscles on increase trials (p less than .01), a behavioral activity previously associated with augmented rather than diminished cortical negativity. On increase trials slow potentials shifted toward positivity just prior to heart rate deceleration (the latter effect confirming activation of the baroreceptors).

Effects of inhaled nicotine on instrumental learning of blood pressure responses

Abstract: The present study investigated the effects of biofeedback of arterial blood pressure on cortical, peripheral, and psychological measures and the dependence of these effects on nicotine. Four groups of subjects, nonsmokers, and habitual smokers who smoked cigarettes during the experimental sessions containing 0.3, 0.8, or 1.5 mg nicotine, respectively, participated in a feedback paradigm in which continuous feedback of mean blood pressure was provided for intervals of 8 s each. While tonic blood pressure did not differ between the groups, the ability to modulate blood pressure (under feedback conditions) was restricted in smokers as compared to nonsmoking subjects; increasing nicotine dosage was accompanied by poorer performance. Independently of habitual smoking and nicotine doses, heart rate increased during feedback and under conditions of blood pressure increase. In smokers, activity in the alpha band was reduced in a dose-dependent manner. Slow cortical potentials (SCPs) during the feedback interval varied with self-induced blood pressure changes in nonsmokers (blood pressure increase was accompanied by reduced surface-negative potential shifts and vice versa), while SCP variations during feedback conditions were small in smokers, more so under the influence of 0.3 and 0.8-mg nicotine, less so under 1.5 mg. Verbal reports suggest that awareness of performance strategies may not be a necessary variable for performance on the blood pressure regulation task.