Halszka Oginska

DIURNAL PATTERNS OF ACTIVITY OF THE ORIENTING AND EXECUTIVE ATTENTION NEURONAL NETWORKS IN SUBJECTS PERFORMING A STROOP-LIKE TASK: A FUNCTIONAL MAGNETIC RESONANCE IMAGING STUDY

Attentional processes are fundamental to good cognitive functioning of human operators. The purpose of this study was to analyze the activity of neuronal networks involved in the orienting attention and executive control processes from the perspective of diurnal variability. Twenty-three healthy male volunteers meeting magnetic resonance (MR) inclusion criteria performed the Stroop Color-Word task (block design) in the MR scanner five times/day (06:00, 10:00, 14:00, 18:00, 22:00 h). The first scanning session was scheduled 1–1.5 h after waking. Between MR sessions, subjects performed simulated driving tasks in stable environmental conditions, with controlled physical activity and diet. Significant activation was found in brain regions related to the orienting attentional system: the parietal lobe (BA40) and frontal eye-fields (FEFs). There were also activations in areas of the executive control system: the fronto-insular cortex (FIC), dorsal anterior cingulate cortex (dACC), presupplementary motor area (preSMA), supplementary motor area (SMA), basal ganglia, middle temporal (MT; BA21), and dorsolateral prefrontal cortex (DLPFC), as a part of the central executive network. Significant deactivations were observed in the rostral anterior cingulate cortex (rACC), posterior cingulate cortex (PCC), superior frontal gyrus (SF), parietal lobe (BA39), and parahippocampal that are thought to comprise the default mode network (DMN). Additionally, the activated regions included bilaterally lingual gyrus and fusiform gyrus. The insula was bilaterally deactivated. Visual attention controlled by the goal-oriented attention system and comprising top-down and bottom-up mechanisms, activated by Stroop-like task, turned out to be prone to diurnal changes. The study results show the occurrence of time-of-day–related variations in neural activity of brain regions linked to the orienting attentional system (left parietal lobe—BA40, left and right FEFs), simultaneously providing arguments for temporal stability of the executive system and default mode network. These results also seem to suggest that the involuntary, exogenous (bottom-up) mechanism of attention is more vulnerable to circadian and fatigue factors than the voluntary (top-down) mechanism, which appear to be maintained at the same functional level during the day. The above phenomena were observed at the neural level. (Author correspondence: marek@uj.edu.pl)

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.

Neural networks related to pro-saccades and anti-saccades revealed by independent component analysis

The saccadic eye movement system provides an excellent model for investigating basic cognitive processes and flexible control over behaviour. While the mechanism of pro-saccades (PS) is well known, in the case of the anti-saccade task (AS) it is still not clear which brain regions play a role in the inhibition of reflexive saccade to the target, nor what is the exact mechanism of vector inversion (i.e. orienting in the opposite direction). Independent component analysis (ICA) is one of the methods being used to establish temporally coherent brain regions, i.e. neural networks related to the task. In the present study ICA was applied to fMRI data from PS and AS experiments. The study revealed separate networks responsible for saccade generation into the desired direction, the inhibition of automatic responses, as well as vector inversion. The first function is accomplished by the eye fields network. The inhibition of automatic responses is associated with the executive control network. Vector inversion seems to be accomplished by the network comprising a large set of areas, including intraparietal sulcus, precuneus/posterior cingulate cortices, retrosplenial and parahippocampal. Those regions are associated with the parieto-medial temporal pathway, so far linked only to navigation. These results provide a new insight into understanding of the processes of the inhibition and vector inversion.

Chronotype and personality factors of predisposition to seasonal affective disorder.

The study aimed to recognize the personality factors of a predisposition to seasonal mood fluctuations in a non-clinical sample. A group of 101 subjects (57 women, 44 men; mean age 26.4 ± 6.5 years) completed a battery of tests comprising a Seasonal Pattern Assessment Questionnaire (SPAQ), Chronotype Questionnaire (ChQ), a NEO-Five Factor Inventory and a Coping Inventory for Stressful Situations (CISS). A smaller sample (n = 44) completed a Winter Blues Scale (WBS). Women scored significantly higher than men in seasonality (p = 0.014), neuroticism (p = 0.049), agreeableness (p = 0.010), and avoidance-oriented coping style (p = 0.041). Subjects with seasonal affective disorder (SAD) (n = 41) or sub-SAD (n = 33), as diagnosed with SPAQ, exhibited higher levels of neuroticism (p = 0.017) and openness (p = 0.016) in comparison to non-SAD individuals. The latter declared a less frequent avoidance coping style. Both measures of seasonality, i.e. the SPAQ Global Seasonality Score and WBS, correlated significantly (r = 0.28 and 0.44, respectively) with the subjective amplitude of the circadian rhythm, as described with the “distinctness” scale of ChQ. Female gender, neuroticism and openness were confirmed as factors linked to seasonal mood variability. Additionally, the study revealed an association between susceptibility to mild winter depression and an avoidance-oriented coping style. The avoidance coping style was correlated positively with all the aspects of seasonality described by SPAQ (correlation coefficients from 0.21 to 0.34). Both sub-types of avoidance-oriented style, i.e. distraction and social diversion, were associated with marked subjective seasonal changes in sleep length, mood and the energy level. While the subjective amplitude of circadian rhythm proved to be connected with seasonality, the subjective acrophase of the rhythm (morningness–eveningness preference) did not. It may be hypothesized that sensitivity to natural environmental conditions/synchronizers is a separate individual trait shaping the subject’s proneness to energy and mood changes both in diurnal and year scale, i.e. circadian and seasonal mood variations.

Chronic sleep deficit and performance of a sustained attention task : an electrooculography study

Electrooculography (EOG) was used to explore performance differences in a sustained attention task during rested wakefulness (RW) and after 7 days of partial sleep deprivation (SD). The RW condition was based on obtaining regular sleep, and the SD condition involved sleep restriction of 3 h/night for a week resulting in a total sleep debt of 21 h. The study used a counterbalanced design with a 2-wk gap between the conditions. Participants performed a sustained attention task for 45 min on four occasions: 10:00–11:00, 14:00–15:00, 18:00–19:00, and 22:00–23:00 h. The task required moving gaze and attention as fast as possible from a fixation point to a target. In each session, 120 congruent and 34 incongruent stimuli were presented, totaling 1232 observations/participant. Correct responses plus errors of omission (lapses) and commission (false responses) were recorded, and the effect of time-of-day on sustained attention following SD was investigated. The analysis of variance (ANOVA) model showed that SD affected performance on a sustained attention task and manifested itself in a higher number of omission errors: congruent stimuli (F(1,64) = 13.3, p < .001) and incongruent stimuli (F(1,64) = 14.0, p < .001). Reaction times for saccadic eye movements did not differ significantly between experimental conditions or by time-of-day. Commission errors, however, exhibited a decreasing trend during the day. The visible prevalence of omissions in SD versus RW was observed during the mid-afternoon hours (the so-called post-lunch dip) for both congruent and incongruent stimuli (F(1,16) = 5.3, p = .04 and F(1,16) = 5.6, p = .03, respectively), and at 18:00 h for incongruent stimuli (F(1,13) = 5.7, p = .03). (Author correspondence: magda.fafrowicz@uj.edu.pl)

Measuring individual vulnerability to sleep loss—the CHICa scale

The aim of this project was to construct a psychometrically satisfying scale to describe subjective reactions to sleep deprivation. First, on the basis of a literature review, a list of items was generated which reflected the negatively affected mood and reduced wellbeing associated with sleep loss. Additionally, psychology students were asked to describe their cognitive and emotional symptoms following a night with curtailed sleep. As a result, 69 items were included in the experimental set. University students (n = 102, females, mean age 22.5 ± 1.9 years) completed the form several times during 1 week in June (while preparing for examinations) and on a free day in September; a total of 460 forms were collected. The final, 26‐item version of the scale was validated in a sleep deficit experiment lasting 1 week, conducted with 25 female participants (mean age 23.4 ± 1.9 years). Factor analysis showed 71.7% of total variance explained by four components: impaired thermoregulation (C for cold), disrupted appetite (H for hunger), affective problems (I for irritability) and lowered level of cognitive functioning (Ca for cognitive attenuation). A Polish version of the CHICa scale showed satisfactory psychometric properties. Cronbachs alpha of the subscales were between 0.90 and 0.95. All four subscales exhibited a significant increase with an experimental 3‐h daily sleep restriction over a period of 1 week; cognitive attenuation was the most symptomatic. Cognitive problems (reduced concentration, comprehension and accuracy) and a lack of energy seem to be the most specific subjective manifestations of the chronic sleep deficit state. CHICa may be helpful in research on inter‐and intra‐individual differences and on the efficacy of various counteractive treatments for the consequences of sleep deprivation.

Scale-Free Fluctuations in Behavioral Performance: Delineating Changes in Spontaneous Behavior of Humans with Induced Sleep Deficiency

The timing and dynamics of many diverse behaviors of mammals, e.g., patterns of animal foraging or human communication in social networks exhibit complex self-similar properties reproducible over multiple time scales. In this paper, we analyze spontaneous locomotor activity of healthy individuals recorded in two different conditions: during a week of regular sleep and a week of chronic partial sleep deprivation. After separating activity from rest with a pre-defined activity threshold, we have detected distinct statistical features of duration times of these two states. The cumulative distributions of activity periods follow a stretched exponential shape, and remain similar for both control and sleep deprived individuals. In contrast, rest periods, which follow power-law statistics over two orders of magnitude, have significantly distinct distributions for these two groups and the difference emerges already after the first night of shortened sleep. We have found steeper distributions for sleep deprived individuals, which indicates fewer long rest periods and more turbulent behavior. This separation of power-law exponents is the main result of our investigations, and might constitute an objective measure demonstrating the severity of sleep deprivation and the effects of sleep disorders.

Different Types of Errors in Saccadic Task Are Sensitive to Either Time of Day or Chronic Sleep Restriction

Circadian rhythms and restricted sleep length affect cognitive functions and, consequently, the performance of day to day activities. To date, no more than a few studies have explored the consequences of these factors on oculomotor behaviour. We have implemented a spatial cuing paradigm in an eye tracking experiment conducted four times of the day after one week of rested wakefulness and after one week of chronic partial sleep restriction. Our aim was to verify whether these conditions affect the number of a variety of saccadic task errors. Interestingly, we found that failures in response selection, i.e. premature responses and direction errors, were prone to time of day variations, whereas failures in response execution, i.e. omissions and commissions, were considerably affected by sleep deprivation. The former can be linked to the cue facilitation mechanism, while the latter to wake state instability and the diminished ability of top-down inhibition. Together, these results may be interpreted in terms of distinctive sensitivity of orienting and alerting systems to fatigue. Saccadic eye movements proved to be a novel and effective measure with which to study the susceptibility of attentional systems to time factors, thus, this approach is recommended for future research.

Chronotype description: In search of a solid subjective amplitude scale

ABSTRACT The term “subjective circadian amplitude” refers to the range or the distinctness of diurnal variations of arousal, that is, the awareness (or lack thereof) of difference between hyper- and hypo-activation phases, the ability to volitionally modulate one’s own psychophysiological state, the strength of morning–evening preferences and flexibility of the rhythm or perceived stability of the circadian phase. The complexity of this construct is the source of difficulties in research and measurement. The psychometric features of distinctness subscales of the Chronotype Questionnaire and the Caen Chronotype Questionnaire are not satisfactory. In search of the solid subjective amplitude (AM) scale, the Rasch analysis was applied to test 12 behavioral descriptors of circadian rhythm distinctness. The results of the Rasch factor analysis showed unidimensionality of the construct. Rating scale diagnostics of the subjective amplitude scale indicated good fit. However, answer category 3 (neutral agreement on the Likert-type, five-point scale) never emerged as modal and step calibrations negated the monotone incrementality of the scale. Rescoring the scale into a four-point category measure yielded satisfactory OUTFIT indices ranging from 0.90 to 1.10. The newly designed AM scale comprised four items referring to small and four to the large amplitude. The four-point answer option was adopted. The data from 234 subjects (53% women; mean age 31.63 ± 12.99 years) were gathered and analyzed. Percent of the total variance explained in Component Analysis (PCA) reached 45.7% (morningness–eveningness (ME) scale – 26.5%, AM scale – 19.2%). There was no correlation between ME and AM scales (Pearsons’s simple correlation coefficient r = −0.018). The internal reliability of the AM scale, as measured with Cronbach’s alpha coefficient, proved to be satisfactory: 0.72 (for ME scale – 0.86). Item-total correlations in the AM scale ranged from 0.433 to 0.774 and were significant at p < 0.001. Confirmatory factorial analysis of AM scale indicated mediocre fit: chi-square/degree of freedom = 3.00, root mean square error of approximation = 0.09, standardized root mean square residual = 0.08, comparative fit index = 0.87, Tucker–Lewis index = 0.82. However, the results of Rasch analysis showed good fit statistics for all items: OUTFIT mean squares range from 0.63 to 1.34 and INFIT mean square range from 0.64 to 1.40. All observed values were ≤1.4, which confirmed the new scale as being unidimensional.f If to consider the chronotype in the context of the classical Borbely’s two-process model of sleep regulation, it may be assumed that ME dimension relates to the tempo of increasing of sleep pressure during the day, that is, it reflects the homeostatic component of the diurnal rhythm of sleepiness. As to the amplitude, it may be supposed that more distinct rhythm (large amplitude) stands for greater vulnerability to the time of day – it resounds the circadian component of the sleep proneness. It seems that distinct diurnal changes of arousal indicate emotional lability and may be associated with emotional responsiveness, which in turn manifests itself in a characteristic style of coping with stressful situations. One may therefore consider the diurnal variability of arousal as a factor increasing individual susceptibility to mood swings and affective disorders.

Seeking a fingerprint: analysis of point processes in actigraphy recording

Motor activity of humans displays complex temporal fluctuations which can be characterised by scale-invariant statistics, thus demonstrating that structure and fluctuations of such kinetics remain similar over a broad range of time scales. Previous studies on humans regularly deprived of sleep or suffering from sleep disorders predicted a change in the invariant scale parameters with respect to those for healthy subjects. In this study we investigate the signal patterns from actigraphy recordings by means of characteristic measures of fractional point processes. We analyse spontaneous locomotor activity of healthy individuals recorded during a week of regular sleep and a week of chronic partial sleep deprivation. Behavioural symptoms of lack of sleep can be evaluated by analysing statistics of duration times during active and resting states, and alteration of behavioural organisation can be assessed by analysis of power laws detected in the event count distribution, distribution of waiting times between consecutive movements and detrended fluctuation analysis of recorded time series. We claim that among different measures characterising complexity of the actigraphy recordings and their variations implied by chronic sleep distress, the exponents characterising slopes of survival functions in resting states are the most effective biomarkers distinguishing between healthy and sleep-deprived groups.