Social hierarchy and adrenocortical stress reactivity in men.

Baseline and stress induced salivary cortisol levels were investigated in 63 army recruits at the beginning and the end of six week boot camp training. At the beginning of the training, the recruits were randomly distributed to nine groups, and weekly measurements of the social hierarchy within each group were obtained. Independent of the social position, baseline levels increased over the first weeks of the training period. Under experimental psychological stress, salivary cortisol levels highly increased in socially dominant subjects (14.0 nmol/l), while only a modest elevation was observed in subordinate men (2.9 nmol/l). Similar differences in response patterns were observed under physical stress. At the end of the training, blunted cortisol responses were observed to both psychological and physical stress. The data suggest a close relationship between social status and pituitary-adrenal responsiveness to psychological stress in men.

Theta power in the EEG of humans during ongoing processing in a haptic object recognition task.

Dynamic changes in spectral theta power (TP) in the EEG over frontal regions were reported previously during the processing of visually presented spatial and verbal tasks [Cereb. Cortex, 7 (1997) 374-385]. Lower TP was found at the beginning compared to the end of processing. In order to test another modality, we examined theta power during the exploration of haptic stimuli with different complexity. A linear correlation between theta power and mean exploration time (as a measure of stimulus complexity) was found at the end of exploration but not at its beginning. These data are in line with our hypothesis since one could expect minimal load of working memory independent of stimulus complexity at the beginning of exploration whereas working memory would have integrated the stimuli of differing complexity into a perceptual model at the end of exploration.

Identification of andrologic patient groups by cluster analysis.

To test the validity of the current andrologic classification system, we performed cluster analysis in 317 andrologic patients involuntarily barren for more than 1 year. For cluster analysis, the spermatologic parameters sperm density, motility, and morphologic features were used since only these parameters contributed significantly to group identification, as revealed by stepwise discriminant function analysis. The optimal number clusters determined by calculation of the variance criterion was five. The resulting five groups partly correspond to the prevailing descriptive classification system as far as the extreme groups of "high-grade oligoteratoasthenozoospermia" and "polyzoospermia" are concerned. Surprisingly, cluster analysis distinguished between two groups of normozoospermia that differed in their mean sperm density. Cluster analysis may prove to become a powerful tool for andrologic classification.

A bioadaptive approach for experimental pain research in humans using laser-evoked brain potentials.

In order to find an experimental approach counteracting habituation in experimental pain research using short infrared laser stimulation in humans we developed a bioadaptive method based on subject's report on painfulness of stimulation (pain report; PR). After determination of the initial relationship between the energy of the laser stimulus and the corresponding PRs, the approach continuously adjusts the intensity of noxious stimuli so that PR is kept constant across time. Each difference between the PR evoked by the actual laser stimulus and the desired PR leads to an increase or decrease of the laser output energy value for the next stimulation with the desired PR proportional to the PR difference as well as to the slope of the initial correlation function between laser energy and corresponding PRs. This method has been applied in a study with nine volunteers. Results show that the approach leads to a constant PR by increasing the laser output energy by 0.01 mJ/s per mm2 on the average. Furthermore, an analysis of the laser-evoked brain potentials (LEPs) recorded from Cz was performed for the first and second half of stimuli. However, no significant changes in latencies or amplitudes of the main LEP components recorded at 210 ms (N210) and 350 ms (P350) were found. The method seems to be useful for different approaches in experimental and clinical pain research.

Power of theta waves in the EEG of human subjects increases during recall of haptic information.

Several studies have reported a functional relationship between spectral power within the theta-band of the EEG (theta-power) and memory load while processing visual or semantic information. We investigated theta power during the processing of different complex haptic stimuli using a delayed recall design. The haptic explorations consisted of palpating the structure of twelve sunken reliefs with closed eyes. Subjects had to reproduce each relief by drawing it 10 s after the end of the exploration. The relationship between mean theta power and mean exploration time was analysed using a regression model. A linear relationship was found between the exploration time and theta power over fronto-central regions (Fp1, Fp2, F3, F7, F8, Fz, C3) directly before the recall of the relief. This result is interpreted in favour of the hypothesis that fronto-central theta power of the EEG correlates with the load of working memory independent of stimulus modality.

Effects of l-tryptophan and various diets on behavioral functions in essential hypertensives.

The effects of tryptophan in combination with two different diets (high-carbohydrate and high-protein diet) on behavioral parameters such as mood, sleep and performance were chronically studied in a group of 34 hypertensive patients undergoing a trial of testing the antihypertensive properties of l-tryptophan. While no major changes in mood were observed, there was a tendency for sleep latency to decrease and sleep duration to increase following tryptophan intake in the intragroup analysis. The administration of tryptophan caused a significant improvement on performance in a concentration task. No significant dietary effects were observed either in combination with tryptophan or in the placebo group. These data again demonstrate behavioral relevance of the precursor amino acid l-tryptophan and suggest a long-term improvement in partial aspects of performance behavior.