Gabriele Freude

Mobile phones modulate response patterns of human brain activity

MOBILE phones emit a pulsed high-frequency electromagnetic field (PEMF) which may penetrate the scalp and the skull. Increasingly, there is an interest in the interaction of this pulsed microwave radiation with the human brain. Our investigations show that these electromagnetic fields alter distinct aspects of the brains electrical response to acoustic stimuli. More precisely, our results demonstrate that aspects of the induced but not the evoked brain activity during PEMF exposure can be different from those not influenced by PEMF radiation. This effect appears in higher frequency bands when subjects process task-relevant target stimuli but was not present for irrelevant standard stimuli. As the induced brain activity in higher frequency bands has been proposed to be a correlate of coherent high-frequency neuronal activity, PEMF exposure may provide means to systematically alter the pattern fluctuations in neural mass activity.

Microwaves emitted by cellular telephones affect human slow brain potentials

Abstract The influence of electromagnetic fields (EMF) emitted by cellular telephones on preparatory slow brain potentials (SP) was studied in two experiments, about 6 months apart. In the first experiment, a significant decrease of SP was found during exposure to EMF in a complex visual monitoring task (VMT). This effect was replicated in the second experiment. In addition to the VMT, EMF effects on SP were analysed in two further, less demanding tasks: in a simple finger movement task to elicit a Bereitschaftspotential (BP) and in a two-stimulus task to elicit a contingent negative variation (CNV). In comparison to the VMT, no significant main EMF effects were found in BP and CNV tasks. The results accounted for a selective EMF effect on particular aspects of human information processing, but did not indicate any influence on human performance, well-being and health.

Auditory probe sensitivity to mental workload changes – an event-related potential study

The goal of this study was to explore the utility of parameters of ERPs for assessment of mental workload during performance of complex tasks. In addition to a baseline auditory oddball task, 15 healthy adult volunteers performed gauge monitoring (Gauge) and mental arithmetic (Math) separately and together. Throughout the task performance three types of auditory stimuli were presented as probes, i.e. 80% 1000 Hz tones, 10% 2000 Hz tones and 10% novel sounds. The ERP components N1 and P3 were analysed, which are assumed to reflect perceptive and central processing resources. The results interpreted in the framework of capacity theory indicate high demand on processing resources already during separate performance of both tasks Gauge or Math. During simultaneous performance the workload on average exceeded the limits of processing capacity: the performance data impaired significantly. The ERP measures N1 and P3 were confirmed in their sensitivity and diagnosticity. By using novel sounds as probes with involuntary attention-capturing properties, one might overcome a problem of the irrelevant probe technique, i.e. whether the operator spends his spare capacity for processing of the irrelevant probes.

Effects of aging and job demands on cognitive flexibility assessed by task switching.

In a cross-sectional, electrophysiological study 91 workers of a big car factory performed a series of switch tasks to assess their cognitive control functions. Four groups of workers participated in the study: 23 young and 23 middle aged assembly line employees and 22 young and 23 middle aged employees with flexible job demands like service and maintenance. Participants performed three digit categorisation tasks. In addition to single task blocks, a cue-based (externally guided) and a memory-based (internally guided) task switch block was administered. Compared to young participants, older ones showed the typical RT-decline. No differences between younger and older participants regarding the local switch costs could be detected despite the source of the current task information. In contrast, whereas the groups did not differ in mixing costs in the cued condition, clear performance decrements in the memory-based mixing block were observed in the group of older employees with repetitive work demands. These findings were corroborated by a number of electrophysiological results showing a reduced CNV suggesting an impairment of task specific preparation, an attenuated P3b suggesting reduced working memory capacity and a decreased Ne suggesting deficits in error monitoring in older participants with repetitive job demands. The results are compatible with the assumption that long lasting, unchallenging job demands may induce several neurocognitive impairments which are already evident in the early fifties. Longitudinal studies are needed to confirm this assumption.

A comparative analysis of the Work Ability Index

BACKGROUND The Work Ability Index (WAI) is a well-established instrument to measure work ability. However, the dimensionality of the WAI remains controversial. AIMS To identify the dimensionality of the WAI and to investigate dependencies of factors and subscales. METHODS The sample analysed in this study consisted of 371 subjects of different occupational groups (teachers, office workers, nursery school teachers and managers). The WAI was measured for all subgroups. Psychometric characteristics of the WAI were investigated using factor analyses with different numbers and different patterns of dependency among the factors. Chi-square analysis and the Comparative Fit Index were used to statistically assess fit quality. RESULTS The group of managers had to be excluded from the analysis as their results were probably overoptimistic due to reporting bias; thus, 324 subjects entered. The one-factor model and an orthogonal two-factor model did not fit the observed correlational structures. A satisfactory fit was obtained using a two-dimensional model with correlated factors. These factors could be interpreted as subjectively estimated work ability and objective health status. Only five of seven items of the WAI could be related unambiguously to one of both factors. CONCLUSIONS From our study, we conclude that using only the total score of the WAI is not adequate for population analysis of and assessment of work ability to individuals. Instead, the two-dimensional structure of the instrument must be taken into account.

The Bereitschaftspotential in preparation to mental activities.

Earlier studies had investigated the Bereitschaftspotential (Bp) under different aspects of muscular activities. The present experiments were designed to test whether the Bp will be affected by the degree of mental load while motor activity is kept constant. Fourteen healthy male subjects had to solve arithmetical tasks under a graduated time pressure (3 categories of tasks). The subjects had to indicate by pressing one of three keys (trigger), which category of task they wanted to solve next. As soon as a key had been pressed, a task appeared on the computer display and disappeared after the time interval corresponding to the selected category. The results had to be entered into a computer via a keyboard. The EEG signals (5 s time constant, 15 Hz upper frequency cut-off) were averaged time-locked to the movement onset, starting 1.5 s before the pressing of the key. Trials with artefacts were rejected from averaging. The Bp was found to be significantly higher when the tasks were to be solved under higher time pressure. We assume that this might be rather an expression of an appropriate self-activation for the expected mental task than due to a different motor preparation.

Predictors of the discrepancy between calendar and biological age

BACKGROUND The rate of ageing can differ considerably between individuals. This might result in major differences between calendar age (CA) and biological age (BA). AIMS To identify work- and health-related predictors of the discrepancy between CA and BA. METHODS The sample analysed in this study consisted of 371 subjects of different occupational groups (teachers, office workers, nursery school teachers and managers). BA was measured with the vitality measuring station, which recorded 45 vitality indicators of physical, mental and social functions. Work ability index, effort-reward imbalance and relaxation inability were measured to determine work- and health-related predictors. RESULTS The greatest discrepancy between CA and BA (9 years) was found for the subgroup of managers, followed by female teachers (5 years). Managers showed also the best results in work ability, the effort-reward balance and relaxation ability. By means of multiple regression analysis, particularly mental attitudes and resources towards work, occupational reward and the body fat percentage were identified as relevant predictors for the discrepancy between CA and BA. CONCLUSIONS Our study indicates that not only health- but also work-related factors are associated with vitality and BA of employees. We assume that measures focused on promoting of health (healthy diet and physical activities) and improving working conditions (e.g. job satisfaction and social support and stress prevention) may also affect the ageing process positively.

Executive control, ERP and pro-inflammatory activity in emotionally exhausted middle-aged employees. Comparison between subclinical burnout and mild to moderate depression

Burnout is a syndrome occurring mainly in individuals with long-term stressful work. The main complaints are emotional exhaustion and reduced performance. Burnout also largely overlaps with depression. Both are characterized by increased incidence of infections due to dysregulation of the immune system, overexpression of pro-inflammatory cytokines and cognitive deficits, particularly related to executive functions. To distinguish between burnout and depression already at the pre-clinical stage, the present double-blinded study compared immunological and cognitive parameters in seventy-six employees from emotionally demanding occupations who were post-hoc subdivided into two groups scoring low (EE-) and high (EE+) in emotional exhaustion and low (DE-) and high (DE+) in depression. Immunological parameters were measured from blood samples. Executive functions were studied by analyzing event-related brain potentials (ERPs) and performance during a task switching paradigm. Psychosocial job parameters were measured with standardized questionnaires. Burnout and mild to moderate depression largely overlapped. However, several subjects showed burnout without depressive symptoms. Higher levels of the pro-inflammatory cytokines IL-6 and IL-12 were correlated with burnout severity and depressive symptoms in male individuals. In the switch task a trend for lower performance in the EE+ vs. EE- group and no difference between DE+ and DE- groups were found. In the ERPs, however, differences were observed which distinguished between subclinical burnout and depression: the terminal contingent negative variation (CNV), indicating preparatory activity and the P3b, related to allocation of cognitive resources were generally reduced in EE+ vs. EE-, whereas no differences were found in the DE+ vs. DE- groups. The frontal P3a was selectively reduced in switch trials in the EE+ vs. EE- group and showed only a trend in DE+ vs. DE-, indicating impairment of executive control in subclinical burnout. Taken together, the results unveil specific immunological changes and declines in brain functions in employees with subclinical burnout that are not apparent in persons with moderate depression. Hence, the combination of immunological, behavioral and ERP methods renders a promising method for distinguishing both syndromes and for improving an early diagnosis of burnout before a clinical stage is reached.

Cognitive Training Sustainably Improves Executive Functioning in Middle-Aged Industry Workers Assessed by Task Switching: A Randomized Controlled ERP Study

Recently, we reported results of a cross-sectional study investigating executive functions in dependence of aging and type of work. That study showed deficits in performance and electrophysiological activity in middle-aged workers with long-term repetitive and unchallenging work. Based on these findings, we conducted a longitudinal study that aimed at ameliorating these cognitive deficits by means of a trainer-guided cognitive training (CT) in 57 further middle-aged workers with repetitive type of work from the same factory. This study was designed as a randomized controlled trail with pre- (t1), post- (t2), and a 3-month follow-up (t3) measure. The waiting control group was trained between t2 and t3. The training lasted 3 months (20 sessions) and was evaluated with the same task switching paradigm used in the previous cross-sectional study. The CT improved performance in accuracy at the behavioral level and affected the electrophysiological correlates of retrieval of stimulus-response sets (P2), response selection (N2), and error detection (Ne), thus unveiling the neuronal background of the behavioral effects. The same training effects were observed in the waiting control group after CT at t3. Moreover, at t3, most of the behavioral and electrophysiological training-induced changes were found stable. Hence, CT appears to be an important intervention for compensating cognitive deficits in executive functions in middle-aged employees with cognitively unchallenging work.

Slow brain potentials in a visual monitoring task

The purpose of this study was to analyse slow brain potentials (SPs) during visual monitoring, needed to perform the clock-monitoring task (CMT). This task was successfully applied in behavioural studies, in which attention capabilities were investigated in dependence on individual factors. Clearly pronounced preparatory SPs were observed during the CMT reflecting a high level of preparation and attention, necessary for achieving high performance accuracy. The well-known influence of task repetition on SPs and the relation between SP and behaviour were confirmed. The practicability of the CMT, the clear and easily detectable SP components and the sensitivity of the present approach makes it recommendable for further applications, e.g. for the evaluation of the effects of occupational/environmental exposures on processes of information processing.