Search PubMed⌕ Search

Biomedical subjects

T Rammsayer

Publications and source records attributed to T Rammsayer.

At least 19 recordsLinked to original sources
PubMed2002

Latent inhibition deficits in high-schizotypal normals: symptom-specific or anxiety-related?

Latent inhibition (LI) is the phenomenon in which subjects who have repeatedly experienced an irrelevant stimulus perform more poorly on a new learning task with that stimulus than with a novel stimulus, presumably because of a decline in stimulus-specific attention. The present article reviews the literature on LI deficits in high-schizotypal normal subjects and schizophrenic patients. Although LI-deficits have been thought to be specific to these groups, evidence is presented that the effects may be related to the anxiety components of high-schizotypality and related pathologies.

Anxiety↗
PubMed2001

Time estimation in schizophrenia: an fMRI study at adjusted levels of difficulty.

fMRI was performed in nine male schizophrenia patients and 15 healthy male controls during an auditory time estimation (timing), a frequency (i.e. pitch) discrimination task, and rest. An adaptive psychophysical approach, the weighted up-down method, was used to adjust individual performance to a level of 75% probability for correct answers. Although performing on the same level of individual difficulty, schizophrenia patients revealed less activations in prefrontal cortex and caudate nucleus, comparing time vs rest. Timing specific differences (i.e. timing vs pitch) between patients and controls were found in the posterior putamen, anterior thalamus, and right medial prefrontal cortex, with patients showing relative hypoactivity. Impairment in time estimation in schizophrenia might be mediated by specific fronto-thalamo-striatal dysfunction.

Adult↗
PubMed2001

Counting models of temporal discrimination.

A three-category task was employed to test counting models for temporal discrimination. Unlike former approaches, the present one is not based on Weber functions. Specifically, the proposed test does not require the implicit but, nevertheless, debatable assumption that the pulse rate of the internal clock is constant for different durations of the standard interval. Furthermore, the present approach does not necessitate specific distributional assumptions about the interpulse times. An experiment was conducted to evaluate the predictions of this generalized counting model. The results are consistent with predictions of the generalized counting model. A further analysis suggests that the pulse rate decreases as the duration of the standard interval increases.

Adult↗
PubMed1997

The effects of sulpiride on psychomotor performance and subjective tolerance.

In many European countries, the substituted benzamide sulpiride is used with antidepressant indication in the dosage range of 150-300 mg on an outpatient population. This raises the concern of possible impairments of psychomotor performance in this dosage range. To address this question, the psychometric effects of 300 mg of sulpiride in comparison with placebo in 12 healthy volunteers was evaluated in this study. In a randomised, double-blind, two-way, within-subjects (cross-over) design, visuomotor performance was assessed using time estimation, critical flicker fusion, and choice reaction time tasks at baseline and 4 h after oral administration of either 300 mg of sulpiride or placebo. In addition, self-ratings on subjective well-being were obtained. Results were evaluated using analysis of covariance (ANCOVA) with baseline levels as covariates. In healthy subjects, 300 mg of sulpiride caused no alteration in time estimation and choice reaction movement time, whereas critical flicker fusion frequency was lower and choice-reaction decision time were prolonged under medication. Self-rating scales showed no significant differences between sulpiride and placebo. Subjects were not able to tell whether they received placebo or sulpiride. This study indicates that sulpiride is subjectively well tolerated at a dosage of 300 mg. However, using psychometric methods, effects are demonstrable that can be interpreted as a reduction of excitatory arousal without causing the subjective experience of sedation. These results call for caution when prescribing the drug to outpatients.

Acoustic Stimulation↗
PubMed1997

Impaired temporal discrimination in Parkinson's disease: temporal processing of brief durations as an indicator of degeneration of dopaminergic neurons in the basal ganglia.

Recent findings suggest that temporal processing of brief durations is a function of dopaminergic neurotransmission in the basal ganglia. Furthermore, there is preliminary evidence of abnormal timing functions in patients suffering from idiopathic Parkinson's disease (PD). In the present study, temporal discrimination of intervals in the range of milliseconds was investigated in 20 PD patients and 20 healthy controls matched for sex and age. Temporal discrimination was significantly impaired in PD patients as compared to healthy controls. For PD patients, additional correlational analyses did not yield any significant relationship between performance on temporal processing and degree of motor impairment or illness duration. However, impairment in temporal processing was associated with dosage of L-dopa substitution and self-rated feelings of depression. The overall pattern of results suggests that deficits in temporal information processing observed in PD patients may represent a trait marker of vulnerability to decreasing levels of dopaminergic activity in the basal ganglia rather than a state-dependent indicator of the acute clinical symptomatology.

Acoustic Stimulation↗
PubMed1995

The perception of temporal structure and auditory evoked brain activity.

The processing and perception of auditory signals depends on the temporal structure of stimulus characteristics. We studied 26 healthy subjects who participated in psychophysical experiments and in electrophysiological recordings of auditory evoked potentials from C2, C3, C4, T3 and T4. Stimuli consisted of tone series presented binaurally as tones or gaps with a base duration of 100 ms. In the psychophysical experiments, difference thresholds as indicators of temporal discrimination performance were significantly lower for tones than for gaps. In the electrophysiological recordings, gaps often failed to elicit N100 components. Tones produced shortest component latencies with largest amplitudes. In addition, brain activity was strongest at C2, and showed a symmetrical fall-off over both hemispheres. N100 components had significantly longer latencies and smaller amplitudes when they were evoked by the end of the gap (i.e. with the continuation of the tone) than by tones. Our data illustrate how the temporal structure of auditory stimuli affects neuronal responses of the brain. Similar effects were observed in psychophysical and electrophysiological experiments, and we were able to demonstrate a direct relationship between subjective sensory thresholds and auditory evoked brain activity.

Adult↗
PubMed1995

Remoxipride versus haloperidol in healthy volunteers: psychometric performance and subjective tolerance profiles.

The aim of the present study was to evaluate the psychometric effects of equivalent clinical doses of remoxipride and haloperidol in comparison with placebo in healthy volunteers. In a double-blind design, either 3 mg haloperidol, 150 mg remoxipride, or placebo were administered to 36 healthy male volunteers ranging in age from 19 to 39 years. Performance was assessed using time estimation, critical flicker fusion, and choice reaction time tasks. In addition, self-ratings on subjective well-being were obtained. In healthy subjects, an acute dose of 3 mg haloperidol caused more severe alteration in cognitive functioning, cortical arousal, and psychomotor performance than a clinically equipotent dose of 150 mg remoxipride. Also, self-rating scales showed that subjective tolerance of remoxipride was partly superior to haloperidol. In general, the results of this study strongly suggest a difference between the psychometric profiles of remoxipride and haloperidol. This difference may be essential for maintaining a high level of compliance, especially in the long-term treatment of psychotic patients.

Adult↗
PubMed1995

Extraversion and alcohol: Eysenck's drug postulate revisited.

Within the framework of Eysenck's drug postulate alcohol is frequently used as an example for a depressant drug that should shift a person's position on the extraversion-introversion axis in the direction of lower arousability. However, only little experimental evidence for differential effects of alcohol on extraverts and introverts appears to exist. Therefore, a placebo-controlled study was designed to investigate the effects of 0.65 g/kg alcohol on temporal discrimination, time estimation, reaction time, movement time, critical flicker fusion frequency (CFF), as well as feelings of activity, alertness, drowsiness, joyfulness, and relaxation in introverts and extraverts. While a main effect of alcohol could be shown for temporal discrimination (p < 0.05), reaction time (p < 0.05), CFF (p = 0.01), and feelings of alertness (p < 0.001) and joyfulness (p < 0.01), significant interactive effects of alcohol and extraversion were only found for time estimation (p < 0.001) and feelings of relaxation (p < 0.01). Extraversion-related differences in movement time (p = 0.05) proved to be insensitive to alcohol. Results are discussed with regard to the pharmacological profile of alcohol and the validity of the drug postulate.

Adult↗
PubMed1994

Extraversion as a modifying factor in catecholamine and behavioral responses to ethanol.

Individual differences in catecholamine response to stress and ethanol were tested in extraverts and introverts on the basis of Eysenck's drug postulate claiming that introverts would be less susceptible to sedative drugs like ethanol. Forty-four healthy males received either 0.8 g/kg ethanol mixed into a drink of caffeine-free cola or a respective placebo and were tested with a stressful mental arithmetic task before and 40 min after the intake of the drink. Plasma catecholamines were determined from blood samples drawn at five defined intervals from an indwelling cannula and self-ratings on deactivation, relaxation, and anxiety were obtained as well as quality and quantity of performance in the arithmetic task. Results showed that there was no difference in catecholamine stress responses between introverts (Ex -) and extraverts (Ex +) before the drink, but that the intake of the fluid (both ethanol and placebo) resulted in higher norepinephrine (NE) increases in Ex - than in Ex +. The combined effects of ethanol and stress yielded larger responses of longer durations in Ex - than in Ex +. The concomitant psychological changes showed larger reductions in anxiety and increases in relaxation as well as larger decrements in quality of performance (% errors) in introverts in spite of their higher catecholamine increases. Thus, the predictions on the basis of arousal theory could not be verified experimentally and the drug postulate has to be modified in the sense that introverts probably have a higher depletion of NE in the central nervous system under physical but not under mental stress which is reflected by higher levels in the plasma and respective decreases in performance and activation.

Adult↗
PubMed1994

[ECG forward simulation with the PC].

This paper describes a simulation program for ECG modelling for use with IBM-compatible computers. The underlying three-dimensional heart model comprising 4,500 units complies with the four criteria for valid ECG-forward modelling established by Gulrajani in 1989: accurate cardiac geometry, element-to-element propagation of the excitation stimulus, definition of action potentials and a suitable means of computing the surface ECG potentials from those measured in the model. For evaluation of the model, simulations of physiological excitation and of pathologies (Wolff-Parkinson-White syndrome, complete AV-block, inferior wall ischaemia) were examined. A high level of correspondence was found between the model situation and the surface ECG. In view of the widespread use of IBM-compatible computers, this new program is well suited for teaching and training purposes.

Arrhythmias, Cardiac↗
PubMed1993

Lowering of body core temperature by exposure to a cold environment and by a 5-HT1A agonist: effects on physiological and psychological variables and blood serotonin levels.

The present study was designed to compare the effects of a pharmacologically induced decrease in body core temperature to the effects observed with lowering of body temperature by exposure to a cold environment. Our special interest was the involvement of 5-HT in thermoregulatory responses. Sixty healthy male volunteers were randomly assigned to one of the following conditions: exposure to normal ambient temperature (28 degrees C) and placebo, exposure to cold ambient temperature (5 degrees C) and placebo, or normal ambient temperature and 10 mg of the partial 5-HT1A agonist ipsapirone. As indicators of physiological responses to lowering of body temperature, tympanic temperature, skin temperature, EMA, metabolic rate, and heart rate were monitored and saliva cortisol levels and peripheral 5-HT concentrations were determined. In addition, ratings on ambient temperature, thermal discomfort, and feelings of irritability were obtained. While lowering of body core temperature was associated with marked counterregulations (decrease of skin temperature, increase in EMA and metabolic rate) and feelings of discomfort, this was not observed with ipsapirone. An increase in cortisol levels was primarily observed in the ipsapirone group and was not reflected by respective changes in whole blood or platelet 5-HT indicating that brain and platelet 5-HT are not related.

Adult↗
PubMed1993

Immune cell and cortisol responses to physically and pharmacologically induced lowering of body core temperature.

In a placebo-controlled double-blind study described by Rammsayer and co-workers in this volume, we investigated the influence of decreased body core temperature (BCT) on responses of cortisol and the immune system. As described in the first paper, the decrease in BCT was achieved by: (a) exposure to ambient cold temperature of 5 degrees C for 20 min (CT group), or (b) application of a 5HT-1a agonist under normal temperature conditions (5HT group). A third group serving as control was exposed to normal temperature and placebo (NT group). The decrease of BCT seen in both CT and 5HT was accompanied by an increase in cortisol. This seemed to be due to stress experience in the CT group and to the pharmacological challenge in the 5HT group. The number of peripheral CD4+ cells was reduced in both experimental groups. This was not mediated by decreased BCT. In the CT group the reduction of CD4+ cells showed no relationship to changes in cortisol. However, in the 5HT group cortisol could be demonstrated to be the mediator of changes in peripheral CD4+ cells.

Adult↗
PubMed1990

Personality related differences in response to 5-HT uptake inhibition.

Conflicting results on clinical effects of serotonergic drugs gave rise to this investigation on the relationship between depression-related personality factors and effects of the 5-HT uptake inhibitor fluoxetine on psychomotor functions and emotional states. In a double-blind, balanced, crossover design, 24 healthy male subjects divided according to scales of "Experiencing of Stress" and "Neuroticism," were tested with a single dose of 60 mg fluoxetine or placebo. Reaction time and feelings of activation and energy of highly neurotic or stressed subjects were deteriorated by fluoxetine while emotionally stable subjects were improved by the drug. The findings were interpreted in terms of personality related differences in 5-HT neurotransmission and receptor sensitivity.

Adult↗
PubMed1990

Temporal discrimination in schizophrenic and affective disorders: evidence for a dopamine-dependent internal clock.

Performance in temporal discrimination of time intervals in the range of milliseconds was compared in 80 healthy subjects, 27 patients with schizophrenic disorders, 33 patients with major depression, 21 patients with dysthymic disorders. For schizophrenic patients as well as for patients with major depression, pronounced deficits in duration discrimination could be demonstrated as compared to the healthy control group (p less than .01). Patients with dysthymic disorders and schizophrenic patients differed significantly from the melancholic group (p less than .01 and p less than .05, respectively). The results are discussed on the basis of the assumption of an internal clock, implying that the clock rate is highest and therefore temporal resolution is best with healthy subjects. With psychiatric patients performance in temporal discrimination was impaired to a slowing down in clock rate and thus decreased temporal resolution. There is strong evidence that changes in clock rate depend on the effective level of dopamine. This leads to the conclusion that temporal discrimination thresholds may be seen as an indicator for deviations from the optimal level of dopaminergic activity in psychiatric patients. In addition, possible effects due to age and medication are discussed.

Analysis of Variance↗
PubMed1990

[Time order error and position effect of a standardized stimulus in discrimination of short time duration].

In comparison judgments of two successively presented time intervals ranging from 30 to 70 msec a time-order error (TOE) as well as a systematic effect depending on the constant position error (CPE) were demonstrated. The effects proved to be independent. Contrary to Vierordt's law, a negative TOE was found. When presenting the standard interval first, an increased hit rate resulting in a positive CPE was established. Furthermore, a test statistic is introduced that allows analysis of experiments utilizing all available information of a subject's psychometric function.

Adult↗
PubMed1989

Dopaminergic and serotoninergic influence on duration discrimination and vigilance.

There is some evidence from animal studies suggesting that dopamine (DA) agonists speed up a hypothesised internal clock, whereas DA antagonists such as haloperidol slow down the clock rate. Furthermore, clinical studies on haloperidol have reported significant deficits in duration discrimination performance (DD). Two double-blind balanced crossover studies with 24 healthy male volunteers each were designed to answer the following questions: 1. Do the DA agonists L-dopa and the DA antagonist haloperidol induce changes in DD? 2. Do the 5-HT uptake inhibitor fluoxetine and the 5-HT receptor antagonist ritanserin induce changes in DD? 3. Can any relationship be demonstrated between changes in DD and changes in vigilance? Haloperidol produced a marked decrease in DD, whereas for the DA agonist no changes could be demonstrated. Performance in DD was slightly improved by the 5-HT agonist and the 5-HT antagonist. Both dopaminergic and serotoninergic changes in DD seemed to be independent of the level of vigilance.

Adult↗
PubMed1989

Is there a common dopaminergic basis of time perception and reaction time?

The effects of 3 mg haloperidol and 125 mg Madopar on duration discrimination (DD) as well as reaction times were tested in a placebo-controlled, double-blind crossover study with 24 healthy male volunteers. Performance in DD was significantly impaired under haloperidol compared to placebo as well as to Madopar. No changes could be demonstrated for Madopar compared to placebo. Similar results were obtained for measures of reaction time. Significant negative correlations between individual changes in DD and measures of reaction time under each drug condition revealed that subjects with drug-induced impairment in DD also show an increase in reaction times. The nearly identical patterns of drug-induced changes in DD and measures of reaction time may be interpreted in terms of a common neural basis.

Adult↗