Sleepy without stimulation: subjective and objective sleepiness in actigraphy-verified natural short sleepers.

Natural short sleepers (NSS)-individuals who report minimal sleepiness or daytime dysfunction despite habitually sleeping less than the recommended amount (i.e., <7 h)-are a focus of growing interest in sleep research. Yet, the predominance of research on NSS has relied on subjective reports of functionality. The present study examined subjective and objective sleepiness among actigraphy-verified NSS in comparison with recommended (7-9 h/day) length sleepers (RLS) who reported similarly minimal daytime dysfunction. The study tested the hypothesis that under conditions of low environmental stimulation, NSS have increased risk of drowsiness and sleep onset, regardless of perceived alertness. The NSS and RLS groups were identified via screening and verified with a 14 day assessment with actigraphy, sleep diaries, and morning ratings of sleep restoration. In-laboratory resting electroencephalography (EEG) data were analysed using a computerised EEG-based algorithm (Vigilance Algorithm Leipzig; VIGALL) to classify second-by-second changes in objective sleepiness ranging from cognitively active alertness to sleep onset. Results demonstrated that NSS exhibited significantly higher drowsiness and sleep onset ('microsleeps') across 15 min of resting EEG despite perceptions of lower subjective sleepiness compared to RLS. Findings suggest that irrespective of perceived sleep restoration and alertness, NSS appear to be at high risk of objective sleepiness that is rapidly unmasked under conditions of low environmental stimulation. Such apparent discrepancy between subjective and objective sleepiness has potentially important public health implications. Future research directions, including tests of mechanisms and tailored sleep extension intervention, are discussed.

The effect of reproductive hormones on women's daily smoking across the menstrual cycle.

BACKGROUND: Women attempt to quit smoking less often than men and are less likely to maintain abstinence. Reproductive hormones have been postulated as a reason for this sex difference, though this remains to be clarified. Research suggests that estradiol and progesterone may influence nicotine addiction, though various methodologies have led to inconsistent findings. The current study aimed to directly examine the effect of reproductive hormones on women's smoking behavior. METHODS: Over the course of one menstrual cycle, twenty-one female smokers recorded the number of cigarettes smoked in a day, as well as their perceived need for and enjoyment of cigarettes smoked. Additionally, they provided 12 urine samples for the measurement of the urinary metabolites of estradiol (estrone-3-glucuronide, E1G) and progesterone (pregnanediol glucuronide, PdG). Multilevel modeling was used to examine the effects of hormone levels as well as hormone change on smoking outcomes. RESULTS: When PdG levels were low, they were inversely associated with daily cigarettes smoked. Furthermore, E1G level was negatively associated with both self-reported need for and enjoyment of cigarettes smoked but not the number of cigarettes smoked. Examining the effect of hormonal change on smoking outcomes revealed a significant interaction between change in PdG and E1G on number of cigarettes smoked such that only a simultaneous drop or increase in both hormones was associated with a greater number of cigarettes. Hormonal change effects on need for and enjoyment of cigarettes were not significant. CONCLUSIONS: The present study suggests that (1) elevated progesterone levels lessen the propensity to smoke in women, (2) estrogen levels influence women's subjective experience of smoking, and (3) simultaneous drops or increases in these hormones are associated with increased smoking.

Resting-state posterior alpha power changes with prolonged exposure in a natural environment.

Exposure to environments that contain natural features can benefit mood, cognition, and physiological responses. Previous research proposed exposure to nature restores voluntary attention - attention that is directed towards a task through top down control. Voluntary attention is limited in capacity and depletes with use. Nature provides unique stimuli that do not require voluntary attention; therefore, the neural resources needed for attention to operate efficiently are theorized to restore when spending time in nature. Electroencephalography reflects changes in attention through fluctuations in power within specific frequencies. The current study (N = 29) measured changes in averaged resting state posterior alpha power before, during, and after a multiday nature exposure. Linear mixed-effects models revealed posterior alpha power was significantly lower during the nature exposure compared to pre-trip and post-trip testing, suggesting posterior alpha power may be a potential biomarker for differences related to exposure to natural and urban environments.

Nature as a potential modulator of the error-related negativity: A registered report.

According to Kaplan's Theory of Attention Restoration (ART), spending time in a natural environment can restore depleted cognitive resources. If this is true, then nature exposure may modulate the error-related negativity (ERN), a component of the event-related brain potential (ERP) that is related to cognitive control and attentional allocation. ART suggests that cognitive resources are restored because the cognitive control networks of the brain are less engaged in nature, suggesting that the ERN may decrease in nature. In the present study, we completed a registered report, examining whether or not spending time in nature would reduce the size of the ERN compared to outdoor testing. Instead, we found that nature significantly increased the amplitude of the ERN. The implications of these results are discussed within the ART framework.

It's about time: The role of temporal variability in improving assessment of executive functioning.

Objective: Executive Functioning (EF) is a group of cognitive abilities related to one's capacity to engage in and maintain goal-oriented behaviours and is one of the most important constructs in neuropsychology. Although EF has been repeatedly linked to response variability and is known to be impacted by various moderators (e.g., stress, sleep, etc.), in practice, EF is typically considered a stable trait. This article seeks to extend this conventional view, by highlighting the additional role of within-subject temporal variability in manifestations of EF and the potential of emerging technologies to better incorporate these dynamics into neuropsychological assessment.Method: Narrative review. Key developmental and dynamical systems concepts for operationalizing different forms of temporal patterns are reviewed. The applicability of these concepts to neuropsychology is then illustrated via specific clinical examples. Ecological Momentary Assessment (EMA) is posited as a potentially critical methodology for capturing temporal patterns in EF, particularly in combination with advances in smartphone technology. The budding literature on cognitive assessment using EMA is reviewed, concluding with a discussion of the challenges to overcome and benefits that could be realized by adopting these methods and technology for clinical use.Conclusions: The conceptualization and assessment of EF can be improved through increased attention to within-subject patterns of temporal variability. Recent technological innovations can facilitate advances in neuropsychological assessment, particularly in our ability to understand and measure the factors that promote and impede EF in daily life.

Neural anticipatory mechanisms predict faster reaction times and higher fluid intelligence.

Higher cognitive ability is reliably linked to better performance on chronometric tasks (i.e., faster reaction times, RT), yet the neural basis of these effects remains unclear. Anticipatory processes represent compelling yet understudied potential mechanisms of these effects, which may facilitate performance through reducing the uncertainty surrounding the temporal onset of stimuli (temporal uncertainty) and/or facilitating motor readiness despite uncertainty about impending target locations (target uncertainty). Specifically, the contingent negative variation (CNV) represents a compelling candidate mechanism of anticipatory motor planning, while the alpha oscillation is thought to be sensitive to temporal contingencies in perceptual systems. The current study undertook a secondary analysis of a large data set (n = 91) containing choice RT, cognitive ability, and EEG measurements to help clarify these issues. Single-trial EEG analysis in conjunction with mixed-effects modeling revealed that higher fluid intelligence corresponded to faster RT on average. When considered together, temporal and target uncertainty moderated the RT-ability relationship, with higher ability being associated with greater resilience to both types of uncertainty. Target uncertainty attenuated the amplitude of the CNV for all participants, but higher ability individuals were more resilient to this effect. Similarly, only higher ability individuals showed increased prestimulus alpha power (at left-lateralized sites) during longer, more easily anticipated interstimulus intervals. Collectively, these findings emphasize top-down anticipatory processes as likely contributors to chronometry-ability correlations.

Changes in Dimensionality and Fractal Scaling Suggest Soft-Assembled Dynamics in Human EEG.

Humans are high-dimensional, complex systems consisting of many components that must coordinate in order to perform even the simplest of activities. Many behavioral studies, especially in the movement sciences, have advanced the notion of soft-assembly to describe how systems with many components coordinate to perform specific functions while also exhibiting the potential to re-structure and then perform other functions as task demands change. Consistent with this notion, within cognitive neuroscience it is increasingly accepted that the brain flexibly coordinates the networks needed to cope with changing task demands. However, evaluation of various indices of soft-assembly has so far been absent from neurophysiological research. To begin addressing this gap, we investigated task-related changes in two distinct indices of soft-assembly using the established phenomenon of EEG repetition suppression. In a repetition priming task, we assessed evidence for changes in the correlation dimension and fractal scaling exponents during stimulus-locked event-related potentials, as a function of stimulus onset and familiarity, and relative to spontaneous non-task-related activity. Consistent with predictions derived from soft-assembly, results indicated decreases in dimensionality and increases in fractal scaling exponents from resting to pre-stimulus states and following stimulus onset. However, contrary to predictions, familiarity tended to increase dimensionality estimates. Overall, the findings support the view from soft-assembly that neural dynamics should become increasingly ordered as external task demands increase, and support the broader application of soft-assembly logic in understanding human behavior and electrophysiology.

ZIP It: Neural Silencing Is an Additional Effect of the PKM-Zeta Inhibitor Zeta-Inhibitory Peptide.

UNLABELLED: Protein kinase M ζ (PKMζ), an atypical isoform of protein kinase C, has been suggested to be necessary and sufficient for the maintenance of long-term potentiation (LTP) and long-term memory (LTM). This evidence is heavily based on the use of ζ inhibitory peptide (ZIP), a supposed specific inhibitor of PKMζ that interferes with both LTP and LTM. Problematically, both LTP and LTM are unaffected in both constitutive and conditional PKMζ knock-out mice, yet both are still impaired by ZIP application, suggesting a nonspecific mechanism of action. Because translational interference can disrupt neural activity, we assessed network activity after a unilateral intrahippocampal infusion of ZIP in anesthetized rats. ZIP profoundly reduced spontaneous hippocampal local field potentials, comparable in magnitude to infusions of lidocaine, but with a slower onset and longer duration. Our results highlight a serious confound in interpreting the behavioral effects of ZIP. We suggest that future molecular approaches in neuroscience consider the intervening level of cellular and systems neurophysiology before claiming influences on behavior. SIGNIFICANCE STATEMENT: Long-term memory in the brain is thought to arise from a sustained molecular process that can maintain changes in synaptic plasticity. A so-called candidate for the title of "the memory molecule" is protein kinase M ζ (PKMζ), mainly because its inhibition by ζ inhibitory peptide (ZIP) interferes with previously established synaptic plasticity and memory. We show that brain applications of ZIP that can impair memory actually profoundly suppress spontaneous brain activity directly or can cause abnormal seizure activity. We suggest that normal brain activity occurring after learning may be a more primary element of memory permanence.

Intrahippocampal Anisomycin Impairs Spatial Performance on the Morris Water Maze.

New memories are thought to be solidified (consolidated) by de novo synthesis of proteins in the period subsequent to learning. This view stems from the observation that protein synthesis inhibitors, such as anisomycin (ANI), administered during this consolidation period cause memory impairments. However, in addition to blocking protein synthesis, intrahippocampal infusions of ANI cause the suppression of evoked and spontaneous neural activity, suggesting that ANI could impair memory expression by simply preventing activity-dependent brain functions. Here, we evaluated the influence of intrahippocampal ANI infusions on allocentric spatial navigation using the Morris water maze, a task well known to require dorsal hippocampal integrity. Young, adult male Sprague Dawley rats were implanted with bilateral dorsal hippocampal cannulae, and their ability to learn the location of a hidden platform was assessed before and following infusions of ANI, TTX, or vehicle (PBS). Before infusion, all groups demonstrated normal spatial navigation (training on days 1 and 2), whereas 30 min following infusions (day 3) both the ANI and TTX groups showed significant impairments in allocentric navigation, but not visually cued navigation, when compared with PBS-treated animals. Spatial navigational deficits appeared to resolve on day 4 in the ANI and TTX groups, 24 h following infusion. These results show that ANI and TTX inhibit the on-line function of the dorsal hippocampus in a similar fashion and highlight the importance of neural activity as an intervening factor between molecular and behavioral processes. SIGNIFICANCE STATEMENT: The permanence of memories has long thought to be mediated by the production of new proteins, because protein synthesis inhibitors can block retrieval of recently learned information. However, protein synthesis inhibitors may have additional detrimental effects on neurobiological function. Here we show that anisomycin, a commonly used protein synthesis inhibitor in memory research, impairs on-line brain function in a way similar to an agent that eliminates electrical neural activity. Since disruption of neural activity can also lead to memory loss, it may be that memory permanence is mediated by neural rehearsal following learning.