Human temporal perception and the circadian system : effects of age, sleep pressure and light

Our intention with this work was to examine cognitive aspects of temporal regulation in humans and delineate possible connections to the circadian and sleep homeostatic systems. In the first experiment reported here, we assessed cognitive temporal orientation on the twenty-four hours scale, operationalized here as the conscious awareness about time of day in absence of external time cues. We studied two age groups under conditions of both high and low sleep pressure. Both age groups tended to overestimate actual time of day under both condtions, but this overestimation was more pronounced in older participants and significantly so under conditions of sustained wakefulness. Under both sleep pressure conditions, both age groups displayed a circadian oscillation in estimation errors which ran parallel to the endogenously generated oscillation in core body temperature. In the younger participants, under conditions of sustained wakefulness, this pattern was combined with an overall increase in the magnitude of estimation errors. Our results gave evidence that interval timing may provide a basis for cognitive temporal orientation via a mechanism of temporal integration. In two further studies, we assessed interval timing in young, healthy male participants for several stimulus magnitudes in the seconds range using temporal production and temporal reproduction under sustained wakefulness and controlled multiple 75 min sleep episodes. During temporal production conducted under controlled napping conditions all durations were over-produced and a slight linear increase in this behavior was observed across the protocol. During the reproduction task under napping conditions, smaller durations were over-reproduced but larger durations were under-reproduced, particularly during the biological night. During temporal production conducted under sustained wakefulness, all durations were under-produced. During reproduction, smaller durations were over-reproduced, especially during the second half of the protocol. Larger durations were under-reproduced under conditions of sustained wakefulness. Our findings suggest a rather weak effect of circadian phase on interval timing and a slightly stronger effect of elevated sleep pressure. We also observed a large degree of inter-individual variability in interval timing behavior which probably reflects the influence of further variables. Finally, we present an investigation into the effects of differential computer screen illumination on temporal perception. We found that interval timing responses are typically lowered under LED-screen illumination when compared to exposure to a CCFL-illuminated computer screen. In summary, we have demonstrated a possible relationship between interval timing and cognitive temporal orientation and were able to show that interval timing needs to be tested under strictly controlled conditions using several methods and stimulus durations in parallel. Our results regarding the effects of differential screen illumination technologies on interval timing should be of great interest to the development of biologically and ergonomically optimized user interfaces for information technology

Modeling circadian and sleep-homeostatic effects on short-term interval timing

Short-term interval timing i.e., perception and action relating to durations in the seconds range, has been suggested to display time-of-day as well as wake dependent fluctuations due to circadian and sleep-homeostatic changes to the rate at which an underlying pacemaker emits pulses; pertinent human data being relatively sparse and lacking in consistency however, the phenomenon remains elusive and its mechanism poorly understood. To better characterize the putative circadian and sleep-homeostatic effects on interval timing and to assess the ability of a pacemaker-based mechanism to account for the data, we measured timing performance in eighteen young healthy male subjects across two epochs of sustained wakefulness of 38.67 h each, conducted prior to (under entrained conditions) and following (under free-running conditions) a 28 h sleep-wake schedule, using the methods of duration estimation and duration production on target intervals of 10 and 40 s. Our findings of opposing oscillatory time courses across both epochs of sustained wakefulness that combine with increasing and, respectively, decreasing, saturating exponential change for the tasks of estimation and production are consistent with the hypothesis that a pacemaker emitting pulses at a rate controlled by the circadian oscillator and increasing with time awake determines human short-term interval timing; the duration-specificity of this pattern is interpreted as reflecting challenges to maintaining stable attention to the task that progressively increase with stimulus magnitude and thereby moderate the effects of pacemaker-rate changes on overt behavior

Exercise-induced sweat nitrogen excretion: evaluation of a regional collection method using gauze pads

Summary: The exercise-induced sweat nitrogen excretion was investigated during a 45-minute run at moderate intensity on a treadmill. Sweat was collected with a regional collection technique using gauze pads and compared with the whole-body wash-down (WBW) method. In the regional collection, sweat was sampled from the upper back (UB), lower back (LB), abdomen (AB), and thigh (TH). Additionally, the relation of sweat urea, ammonia, and amino acids was investigated with the regional collection method during a second 45-minute run. Independent of the sweat collection method, a significant and positive correlation was found between sweat rate and the excretion rate of the largest nitrogen fraction urea, suggesting that the sweating response to exercise might be one of the most important factors determining absolute sweat nitrogen losses. The urea nitrogen excretion was nearly 140 mg·h−1 in the second run, representing the largest nitrogen fraction. Ammonia nitrogen and amino acid-derived nitrogen rate were approximately 30 mg·h−1 and 10 mg·h−1, respectively. The comparison of the sampling methods during the first run revealed that the urea nitrogen rate was significantly higher, but the ammonia nitrogen rate significantly lower in the WBW. After summing urea and ammonia nitrogen, no significant difference between the methods was observed anymore, except for UB. It is concluded that the regional collection method using gauze pads is a valuable approach to measure exercise-induced sweat nitrogen losses during moderate running exercis

An fMRI investigation of the relationship between future imagination and cognitive flexibility

While future imagination is largely considered to be a cognitive process grounded in default mode network activity, studies have shown that future imagination recruits regions in both default mode and frontoparietal control networks. In addition, it has recently been shown that the ability to imagine the future is associated with cognitive flexibility, and that tasks requiring cognitive flexibility result in increased coupling of the default mode network with frontoparietal control and salience networks. In the current study, we investigated the neural correlates underlying the association between cognitive flexibility and future imagination in two ways. First, we experimentally varied the degree of cognitive flexibility required during future imagination by manipulating the disparateness of episodic details contributing to imagined events. To this end, participants generated episodic details (persons, locations, objects) within three social spheres; during fMRI scanning they were presented with sets of three episodic details all taken from the same social sphere (Congruent condition) or different social spheres (Incongruent condition) and required to imagine a future event involving the three details. We predicted that, relative to the Congruent condition, future simulation in the Incongruent condition would be associated with increased activity in regions of the default mode, frontoparietal and salience networks. Second, we hypothesized that individual differences in cognitive flexibility, as measured by performance on the Alternate Uses Task, would correspond to individual differences in the brain regions recruited during future imagination. A task partial least squares (PLS) analysis showed that the Incongruent condition resulted in an increase in activity in regions in salience networks (e.g. the insula) but, contrary to our prediction, reduced activity in many regions of the default mode network (including the hippocampus). A subsequent functional connectivity (within-subject seed PLS) analysis showed that the insula exhibited increased coupling with default mode regions during the Incongruent condition. Finally, a behavioral PLS analysis showed that individual differences in cognitive flexibility were associated with differences in activity in a number of regions from frontoparietal, salience and default-mode networks during both future imagination conditions, further highlighting that the cognitive flexibility underlying future imagination is grounded in the complex interaction of regions in these networks

Genetic Determinants of Time Perception Mediated by the Serotonergic System

Background: The present study investigates neurobiological underpinnings of individual differences in time perception. Methodology: Forty-four right-handed Russian Caucasian males (18–35 years old) participated in the experiment. The polymorphism of the genes related to the activity of serotonin (5-HT) and dopamine (DA)-systems (such as 5-HTT, 5HT2a, MAOA, DAT, DRD2, COMT) was determined upon the basis of DNA analysis according to a standard procedure. Time perception in the supra-second range (mean duration 4.8 s) was studied, using the duration discrimination task and parametric fitting of psychometric functions, resulting in individual determination of the point of subjective equality (PSE). Assuming the ‘dual klepsydra model ’ of internal duration representation, the PSE values were transformed into equivalent values of the parameter k (kappa), which is a measure of the ‘loss rate ’ of the duration representation. An association between time representation parameters (PSE and k, respectively) and 5-HT-related genes was found, but not with DArelated genes. Higher ‘loss rate ’ (k) of the cumulative duration representation were found for the carriers of genotypes characterized by higher 5-HT transmission, i.e., 1) lower 5-HT reuptake, known for the 5-HTTLPR SS polymorphism compared with LL, 2) lower 5-HT degradation, described for the ‘low expression ’ variant of MAOA VNTR gene compared with ‘high expression ’ variant, and 3) higher 5-HT2a receptor density, proposed for the TT polymorphism of 5-HT2a T102C gene compared with CC

Separate neural representations of prediction error valence and surprise: Evidence from an fMRI meta-analysis.

Learning occurs when an outcome differs from expectations, generating a reward prediction error signal (RPE). The RPE signal has been hypothesized to simultaneously embody the valence of an outcome (better or worse than expected) and its surprise (how far from expectations). Nonetheless, growing evidence suggests that separate representations of the two RPE components exist in the human brain. Meta-analyses provide an opportunity to test this hypothesis and directly probe the extent to which the valence and surprise of the error signal are encoded in separate or overlapping networks. We carried out several meta-analyses on a large set of fMRI studies investigating the neural basis of RPE, locked at decision outcome. We identified two valence learning systems by pooling studies searching for differential neural activity in response to categorical positive-versus-negative outcomes. The first valence network (negative > positive) involved areas regulating alertness and switching behaviours such as the midcingulate cortex, the thalamus and the dorsolateral prefrontal cortex whereas the second valence network (positive > negative) encompassed regions of the human reward circuitry such as the ventral striatum and the ventromedial prefrontal cortex. We also found evidence of a largely distinct surprise-encoding network including the anterior cingulate cortex, anterior insula and dorsal striatum. Together with recent animal and electrophysiological evidence this meta-analysis points to a sequential and distributed encoding of different components of the RPE signal, with potentially distinct functional roles

THE RELATIONSHIP BETWEEN THE ENGLISH LANGUAGE AND SOCIAL CLASS Analysis of the BBC Series Sherlock

The aim of the study is to analyse the language used in the BBC series Sherlock. The focus is on the way the show portrays characters with different social backgrounds and their use of the English language, and whether this reinforces certain ways of thinking about social class. The primary data analysed are the complete DVD collection of all 4 seasons of Sherlock and their transcripts, containing 12 episodes and scripts in total. Manual and digital methods were used for studying linguistic features of standard and non-standard English used by different characters in the series, e.g. in grammar, pronunciation, violation of discourse features and pronunciation. Second, a questionnaire distributed to members of a BBC Sherlock fan forum yielded information about how the audience perceived the modern Sherlock series and how they think it reinforced certain ways of thinking about social class. The main findings showed that a certain reappearing pattern of non-standard linguistic features used in the entire series could be identified and connected to certain characters. The combination of both parts of the results was important and showed that the representation of social class in the BBC Sherlock series highlights the challenge of representing modern society

DIGLOSSIE IN DEUTSCHSCHWEIZER SPITÄLERN. Studie zu Sprachgebrauch und Spracheinstellung von MitarbeiterInnen

The concomitant presence and usage of two varieties of German, namely Swiss German and Standard German, is characteristic for German-speaking Switzerland. This linguistic situation is mirrored in the region’s hospitals or, more strictly speaking, in their staff‘s communication. This study aims to examine the awareness of the usage of the two varieties in hospitals in German-speaking Switzerland, taking into account both authochthonous and allochthonous employees. The questions formulated to find out are as follows: Which variety is used when, according to which criteria, by authochthonous versus allochthonous employees? What subjective reasons are given for the choice of one variety over the other? To answer these questions, data was collected with the help of an online questionnaire and six guideline-based, in-depth interviews. The results show four different selection criteria (addressee, situation, objective, and region) for using one or the other variety. Moreover, the reasons given for the choice of variety revealed that both Swiss German and Standard German are attributed individual functions and characteristics