Temporal unpredictability increases error monitoring as revealed by EEG-EMG investigation.

Reacting in an unpredictable context increases error monitoring as evidenced by greater error-related negativity (ERN), an electrophysiological marker linked to an evaluation of response outcomes. We investigated whether ERN also increased when participants evaluated their responses to events that appeared in unpredictable versus predictable moments in time. We complemented electroencephalographic (EEG) analysis of cortical activity by measuring performance monitoring processes at the peripheral level using electromyography (EMG). Specifically, we used EMG data to quantify how temporal unpredictability would affect motor time (MT), the interval between the onset of muscle activity, and the mechanical response. MT increases following errors, indexing online error detection, and an attempt to stop incorrect actions. In our temporally cued version of the stop-signal task, symbolic cues predicted (temporally predictable condition) or not (temporally unpredictable condition) the onset of a target. In 25% of trials, an auditory signal occurred shortly after the target presentation, informing participants that they should inhibit their response completely. Response times were slower, and fewer inhibitory errors were made during temporally unpredictable than predictable trials, indicating enhanced control of unwanted actions when target onset time was unknown. Importantly, the ERN to inhibitory errors was greater in temporally unpredictable relative to temporally predictable conditions. Similarly, EMG data revealed prolonged MT when reactions to temporally unpredictable targets had not been stopped. Taken together, our results show that a temporally unpredictable environment increases the control of unwanted actions, both at cortical and peripheral levels, suggesting a higher subjective cost of maladaptive responses to temporally uncertain events.

Inconvenient correlation - RT-BOLD relationship for homogeneous and fast reactions.

Reaction time (RT), a widely used measure of human performance in experimental psychology, has recently been included as a regressor of interest in functional magnetic resonance imaging (fMRI) data analysis. Few studies reported RT-related brain regions, but the nature of this activity is not fully understood. We aimed at exploring this topic by implementing a simple saccadic task which evokes fast and homogeneous reactions that require only the basic neural processes. Thus, a spatial cueing paradigm was chosen and implemented in a simultaneous fMRI and eye-tracking experiment. As a result, we found a wide set of brain regions showing trial-by-trial correlations of blood-oxygenation-level-dependent (BOLD) signal with saccadic RT. These regions included medial and lateral frontal lobes, bilateral intraparietal sulci, anterior insular cortices as well as the right thalamus and medial visual cortex. Further analysis was conducted in order to verify quantitatively the impact of a "time on task" effect on task-related hemodynamic responses (HDRs). The results provide evidence that even a small difference in RTs can be linked with significant increase of HDR in task-related areas. Moreover, this increase is not linear, but rather quadratic. Our findings highlight the importance of controlling for RT in fMRI data analysis when contrasting conditions that vary in RT to avoid the misinterpretation of results.

Internal and external factors influencing time-related injury risk in continuous shift work.

Time-related accident risk in shift work may be attributed to internal factors, such as fatigue, level of performance, sleep propensity, and to some external factors, like shift system, physical and social environment. Six hundred and sixty-eight events in the metallurgical industry have been analysed in terms of time of day, time on task, consecutive day of the shift block, day of the week, and season. The injury rate was similar on all shifts but more severe accidents happened in the nighttime. Somewhat more injuries occurred in the second half of the shift, in the second part of a shift block, and in summer compared with winter. There were fewer injuries at weekends.

Gender, ageing, and shiftwork intolerance.

The study investigated the hypothetical differences between male and female shiftworkers in their susceptibility to shiftwork-related health and social problems, with the special reference to the role of the age factor. The comparison concerned two matched-for-age-and-occupation groups of men and women, each of 83 persons, selected from the larger studied population of more than 700 workers in a Polish steel plant. The subjects were crane-operators employed in the same forward-rotated, three-shift, four-team shift system, 4:4:4 with shift changes at 06:00, 14:00, 22:00; and 48 h off following each shift block. The investigation comprised a battery of questionnaires on demographic characteristics, sleep quantity and quality, subjective health complaints, and opinions on shiftwork. The analysis of data revealed that men slept more than women, especially when working on the afternoon and night shifts. The differences became more striking and significant for all work shifts and days-off when related to declared individual sleep requirements. Women experienced more sleep disturbances than men and suffered more frequently from drowsiness during work, especially when working the morning shift. The ratings of subjective health were lower in women, with exception of respiratory complaints. Women generally suffered more than men from symptoms considered as specific to the 'intolerance syndrome', i.e. psychoneurotic, digestive, circulatory, and those of chronic fatigue. However, after passing the 'critical decade' of 40-50 years their subjective health generally improved, whereas in males one observed the consequent deterioration of health with advancing age. Women more often complained about their health and went to see the doctor, but on the other hand, they did not tend to quit shiftwork as often as did their male counterparts.

[Chrono-type as a factor of shiftwork tolerance in women]. / Chronotypologiczne uwarunkowania tolerancji pracy zmianowej u kobiet.

Almost all physiological and psychological functions of human beings reveal circadian variations. The parameters of those rhythms differ in various subjects dependently on their individual diurnal characteristics, named here chrono-type. The difference in phase of maximal arousal is particularly apparent so that it implies the distinction between the morning and the evening types. The comparative study of both chrono-types was done with regard to the subjective health, sleep disorders and disturbances, attitudes towards shiftwork and physical fitness as measured by indirect prediction of the maximal oxygen uptake. In spite of differences in the bedtime and awaking time, representatives of morning and evening type did not differ when considering the amount of sleep. Both groups slept about one hour less than subjectively required. The analysis of sleep disorders (during days with various shifts and days off) showed that their configuration was different in compared groups. Morning types more often woke before proper time and suffered from frequent mid-sleep awakenings. They had also more difficulties in falling asleep and felt tired after awakening when working night shift. Evening types reported more often difficulties in awakening (independently on work shift) and complained low well-being or tiredness after awakening when working morning or afternoon shift and during days off. The percentage of morning types reporting various sleep disturbances of external (noise, daylight) or internal (hunger, nervousness) origin was 13 to 74. The corresponding figures for evening types were 4 to 52%. Subjective health was assessed with use of a list of 74 symptoms. It was found that morning individuals significantly more frequently reported fevers and sub-febrile states, itching in heart region, pains or tightness in heart region when nervous and musculoskeletal pains. No significant differences in gastrointestinal complaints were found. Analysis of typical circulatory, respiratory and musculoskeletal syndromes revealed the lower frequency of circulatory and musculoskeletal complaints and more respiratory symptoms in evening types. This latter could be considered as the result of prevalence of smokers in this group. The prediction of maximal oxygen uptake with use of indirect Astrand-Rhythm method showed significantly higher values in evening types. Taking into account that the result of this method is based on the heart rate response to submaximal load--it is highly probable that the difference observed is due to chrono-type related difference in phase of circadian rhythm of heart rate reaction to the load applied on the same time of the day. Both studied groups differed significantly as to the percentage of persons approving the work in shifts.(ABSTRACT TRUNCATED AT 400 WORDS)