Performance analysis of indicators of chaos for nonlinear dynamical systems.

The efficient detection of chaotic behavior in orbits of a complex dynamical system is an active domain of research. Several indicators have been proposed, and new ones have recently been developed in view of improving the performance of chaos detection by means of numerical simulations. The challenge is to predict chaotic behavior based on the analysis of orbits of limited length. In this paper the performance analysis of past and recent indicators of chaos, in terms of predictive power, is carried out in detail using the dynamical system characterized by a symplectic Hénon-like cubic polynomial map.

Associations between post-traumatic stress symptoms and sleep/circadian parameters: Exploring the effect of chronotype as a moderator variable.

The present study aimed at evaluating how post-traumatic stress symptoms (PTSS) are associated with rest-activity circadian and sleep-related parameters, assessed both subjectively (via questionnaires) and objectively (via actigraphy). Specifically, we explored whether chronotype could moderate the association between sleep/circadian parameters and PTSS. Participants (n = 120 adults; mean age 35.6 ± 14; 48 male) were assessed through the Trauma and Loss Spectrum Self Report (TALS-SR) for lifetime PTSS, the reduced version of the Morningness-Eveningness Questionnaire (rMEQ) for chronotype, the Pittsburgh Sleep Quality Index (PSQI) for self-reported sleep quality, and wrist actigraphy for sleep and circadian parameters. Eveningness, poor self-reported sleep quality, lower sleep efficiency (SE), lower interdaily stability (IS), and higher intradaily variability (IV) were correlated with higher TALS-SR scores. Regression analyses showed that IV, SE, and PSQI remained associated with TALS symptomatic domains after adjusting for potentially confounding factors (age and gender). Moderation analysis showed that only the PSQI remained significantly associated with TALS symptomatic domains; however, the interaction with chronotype was not significant. Targeting self-reported sleep disturbances and rest-activity rhythms fragmentation could mitigate PTSS. Although the effect of chronotype as a moderator of the associations between sleep/circadian parameters and PTSS was not significant, eveningness was associated with higher TALS scores, thus confirming the vulnerability of evening types to worse stress reactions.

Late chronotypes, late mealtimes. Chrononutrition and sleep habits during the COVID-19 lockdown in Italy.

The emerging field of chrononutrition provides useful information on how we manage food intake across the day. The COVID-19 emergency, and the corresponding restrictive measures, produced an unprecedented change in individual daily rhythms, possibly including the distribution of mealtimes. Designed as a cross-sectional study based on an online survey, this study aims to assess the chrononutrition profiles (Chrononutrition Profile Questionnaire, CP-Q) in a sample of 1298 Italian participants, during the first COVID-19 lockdown, and to explore the relationship with chronotype (reduced Morningness-Eveningness Questionnaire, rMEQ), sleep quality (Pittsburgh Sleep Quality Index, PSQI) and socio-demographics. Our findings confirm a change in eating habits for 58% of participants, in terms of mealtimes or content of meals. Being an evening chronotype and experiencing poor sleep imply a higher likelihood of changing eating habits, including a delay in the timing of meals. Also, under these unprecedented circumstances, we report that the timing of breakfast is a valuable proxy capable of estimating the chronotype. From a public health perspective, the adoption of this straightforward and low-cost proxy of chronotype might help in the early detection of vulnerable subgroups in the general population, eventually useful during prolonged stressful conditions, as the one caused by COVID-19 pandemic.

Poor sleep quality and unhealthy lifestyle during the lockdown: an Italian study.

BACKGROUND: The lockdown measure implemented to face the 2019 Coronavirus Disease (COVID-19) first wave deeply modified the lifestyle of the Italian population. Despite its efficacy in limiting the number of infections, forced home confinement was paralleled by sleep/wake cycle disruptions, psychological distress and maladaptive coping strategies (i.e., unhealthy behaviours, such as tobacco and alcohol consumption). Under these unprecedented stress conditions, we explored a possible association between poor sleep quality and increased likelihood of engaging in an unhealthy lifestyle. METHODS: A cross-sectional study was conducted by disseminating an online survey via social networks and e-mail. We collected information on demographics, COVID-19-related data, sleep quality, chronotype, circadian misalignment, and lifestyle before and during the lockdown (i.e., consumption of cigarettes, alcoholic beverages, coffee, hypnotics, comfort food and fresh food; practice of physical activity). A global healthiness score was computed to assess participants' modifications in lifestyle since the beginning of the lockdown. RESULTS: 1297 respondents were included in the study: 414 (31.9%) from Northern Italy, 723 (55.8%) from Central Italy, 160 (12.3%) from Southern Italy. The following variables were found to be significant predictors of the adoption of an unhealthy lifestyle since the beginning of the lockdown: poor sleep quality, high BMI and considering the measures adopted by the government to fight the pandemic as excessive. Living in Northern Italy, instead, was associated with healthier habits compared to living in Central Italy. CONCLUSIONS: Poor sleepers may represent the share of the general population who paid the highest price for social isolation. Further investigations are required to explore the role of sleep quality assessment in the identification of individuals vulnerable to unhealthy behaviours under stressful conditions.

Sleep quality mediates the effect of chronotype on resilience in the time of COVID-19.

This study aimed to explore the relationship between chronotype and resilience, sleep quality, and post-traumatic stress reactions during the first COVID-19 lockdown in Italy. An online survey was distributed through social networks during forced home confinement, collecting data from1298 participants of 19 different Italian regions. Chronotype was evaluated using the reduced version of the Morningness/Eveningness Questionnaire (rMEQ); sleep quality was assessed by the Pittsburgh Sleep Quality Index (PSQI); resilience levels were measured by the 10-item version of the Connor-Davidson Resilience Scale (CD-RISC10); post-traumatic stress reactions were assessed by the 6-item version of the Impact of Event Scale (IES6). Resilience and sleep quality were significantly lower in the evening compared to non-evening types, as well as in females as compared to males. Moreover, resilience was negatively correlated with post-traumatic stress reactions and positively correlated with sleep quality. A negative correlation was also reported between sleep quality and post-traumatic stress reactions. Sleep quality was identified as a possible mediator between chronotype and resilience, and between resilience and post-traumatic stress reactions, after controlling for age and sex. These findings provide new insights into the role of chronotype in adapting to continuous stressful situations. Sleep quality seems to mediate the causal path between the antecedents of resilience and the development of trauma. Further research is needed to explore the suitability of primary interventions based on chronobiology and sleep hygiene to mitigate the impact of pandemic-related home confinement measures on mental health among the general population.

The effect of noise on a class of energy-based learning rules.

Westudy the selectivity properties of neurons based on BCM and kurtosis energy functions in a general case of noisy high-dimensional input space. The proposed approach, which is used for characterization of the stable states, can be generalized to a whole class of energy functions. We characterize the critical noise levels beyond which the selectivity is destroyed. We also perform a quantitative analysis of such transitions, which shows interesting dependency on data set size. We observe that the robustness to noise of the BCM neuron (Bienenstock, Cooper, & Munro, 1982; Intrator & Cooper, 1992) increases as a function of dimensionality. We explicitly compute the separability limit of BCM and kurtosis learning rules in the case of a bimodal input distribution. Numerical simulations show a stronger robustness of the BCM rule for practical data set size when compared with kurtosis.

An SVM classifier to separate false signals from microcalcifications in digital mammograms.

In this paper we investigate the feasibility of using an SVM (support vector machine) classifier in our automatic system for the detection of clustered microcalcifications in digital mammograms. SVM is a technique for pattern recognition which relies on the statistical learning theory. It minimizes a function of two terms: the number of misclassified vectors of the training set and a term regarding the generalization classifier capability. We compare the SVM classifier with an MLP (multi-layer perceptron) in the false-positive reduction phase of our detection scheme: a detected signal is considered either microcalcification or false signal, according to the value of a set of its features. The SVM classifier gets slightly better results than the MLP one (Az value of 0.963 against 0.958) in the presence of a high number of training data; the improvement becomes much more evident (Az value of 0.952 against 0.918) in training sets of reduced size. Finally, the setting of the SVM classifier is much easier than the MLP one.

Mobilis in mobile: a probabilistic and chronotopic model of mobility in urban spaces.

In this communication we propose an urban mobility model based on individual random walk driven by a chronotopic action with a deterministic public transportation network. In the absence of chronotopoi the mean field analytic results are found in good agreement with simulations on a computer. When the chronotopoi are switched on, they attract people according to a given law and we obtain a sort of diffusive motion. The model can describe many different kinds of dynamical systems, including biological ones. The work is in progress and the next step will be an empirical test in a concrete case.