Sleep and Biological Rhythms: from Cognition to Clinical Practice

26.04.2026, Sunday, 12:30-14:00

General focus of the symposium:

The two-process model of sleep and wake regulation postulates that individual levels of alertness depend on the interactions between the accumulating homeostatic sleep pressure and circadian arousal signal. As a result of the complex interplay between these two factors, humans experience a great extent of intra- and interindividual variability in their cognitive and affective functioning. The proposed symposium offers comprehensive insights into the biological underpinnings of the discussed phenomena, utilising a broad range of neuroimaging (EEG, MRI, PET) and psychophysiological (pupillometry and salivary melatonin level assessment) methodologies. Starting with sleep-related processes, the initial three studies delineate variability in brain network organisation associated with accumulating sleep debt, and processing of endogenously and exogenously generated stimuli. In more detail, the presentations provide insights into the neural alterations associated with acute and chronic sleep deprivation, followed by neuroanatomical correlates of the frequency of experiencing lucid dreaming, and differences in region-to-region communication during auditory processing under wakefulness and varying levels of sleep depth. In turn, the remaining two talks focus on circadian rhythmicity, demonstrating the important role of external light processing in shaping the associated behavioural outcomes. The fourth presentation will probe the utility of salivary dim light melatonin onset (DLMO) and pupillometry-assessed retinal ganglion cell light sensitivity for diagnosis and phenotyping of delayed sleep-wake phase disorder. Last but not least, the final talk will demonstrate how the interactions of circadian and seasonal rhythmicity, as evidenced by variation in daylength and therefore light exposure, are reflected in the availability of dopamine and mu-opioid receptors, highlighting mechanisms potentially contributing to mood seasonality. As such, the symposium will deepen the audience’s understanding of the sleep- and circadian-related processes, demonstrating the wide variability of tools that can be used for studying the underlying biological mechanisms, together with potential clinical applicability of such knowledge.

12:30 Patrycja Scislewska

University of Warsaw, Faculty of Biology

"Network-Level Reorganization of Brain Functional Connectivity after Total and Chronic Sleep Deprivation"

Although sleep loss is known to impair cognitive performance and emotional regulation, the neural consequences of different types of sleep deprivation remain poorly understood.

In this study, we directly compared acute total sleep deprivation (TSD) and chronic sleep restriction (CSR) to examine how each form of sleep loss alters intrinsic functional brain organization.

In a longitudinal resting-state fMRI design, twenty-eight healthy adults were scanned under three conditions: rested wakefulness (RW), after one night of TSD (~26 h awake), and after five nights of CSR (5 h sleep per night). To quantify disruptions in functional connectivity, we introduced and applied a within-subject Hub Disruption Index, a novel graph-based measure of individual neural reorganization. We further characterized condition-specific effects using Covariate-Constrained Manifold Learning (CCML). Finally, to compare neural changes with subjective experiences, we used psychometric assessment of sleep quality, sleepiness and circadian traits.

Both TSD and CSR led to consistent reorganization of network topology relative to RW but affected distinct functional hubs. Regional changes were most prominent within subsystems of the default mode, frontoparietal, and cerebellar networks. CCML embeddings further supported divergent connectivity patterns between TSD and CSR. Additionally, greater subjective sleepiness was associated with reduced network integration during RW, and circadian phenotype emerged as a key determinant of individual sensitivity to sleep loss.

Acute and chronic sleep loss induce distinct alterations in human functional brain organization. These findings advance mechanistic understanding of sleep deprivation and offer new insights for clinical interventions.

12:45 Karolina Raczek

Doctoral School in the Social Sciences, Jagiellonian University, Krakow, Poland

"Sleep and Biological Rhythms: from Cognition to Clinical Practice"

Becoming aware of the current dream state during ongoing sleep is referred to as lucid dreaming (LD), a phenomenon that shows promise for both clinical and scientific applications. Although LD is infrequent for most, its frequency varies substantially across individuals. While progress has been made, a comprehensive understanding of the neural underpinnings associated with LD remains elusive, with conflicting evidence regarding whether the occurrence of LD is linked to neuroanatomical differences.

The present study investigated the neuroanatomical correlates of LD.

As part of the NeuralArchCon (The Neural Architecture of Consciousness) COST Action, we characterized a large sample of participants (N=785). LD frequency was assessed using the Dream Recall Questionnaire, while brain structure was evaluated via multi-parameter mapping (MPM) quantitative MRI.

We examined the associations between LD frequency and gray matter volume within regions of interest, including the anterior prefrontal cortex, anterior cingulate cortex, supplementary motor area, and hippocampus, while controlling for age, sex, total intracranial volume and general dream recall frequency.

As the largest investigation to date, this study clarifies whether LD frequency is associated with specific structural brain characteristics. The results will be presented and discussed in detail during the presentation.

13:00 Anna Zofia Lesniewska

Institute of Psychology, Jagiellonian University; Faculty of Psychological and Educational Sciences, Université Libre de Bruxelles

"Sleep Stages Affect Low-Gamma Range Effective Cortical Connectivity for 40-Hz Auditory Steady-State Responses"

The 40-Hz auditory steady-state response (ASSR) is a sensitive marker of arousal fluctuations, which has been reported to decrease during deep sleep. However, sleep-related changes in directional connectivity during 40-Hz ASSR remain underexplored.

In this study, we examined how sleep stages affect the 40-Hz ASSR propagation. We focused on the connections between auditory and associative regions in the temporal, prefrontal, and temporo-parietal cortices. We hypothesized that: 1) feedback connections from associative to primary auditory areas will be the most affected by the arousal state changes; 2) associative reciprocal connectivity between prefrontal and temporo-parietal regions will display gradual connectivity reduction with increasing NREM sleep depth, with partial restoration during REM sleep.

EEG data during periodic 40-Hz auditory stimulation were collected during an overnight study from 29 normal-hearing human subjects (including 16 females). Source analysis was used to locate cortical activity, and effective connectivity was assessed using the Directed Transfer Function (DTF) in the 37–43 Hz frequency range.

Our results demonstrated that during deeper sleep (NREM N2 and N3, and REM), both feedforward and feedback connectivity were significantly reduced to a comparable extent. At sleep onset (NREM N1), feedforward disruptions were already robust despite affecting a limited number of pathways, whereas feedback reductions were weaker and increased progressively across REM, NREM N2, and N3 sleep, contradicting our first hypothesis. Our second hypothesis was confirmed: reciprocal connectivity between the prefrontal and parietal associative regions was significantly weakened with increasing sleep depth.

Overall, the reduced propagation of neural signals underlying the 40-Hz ASSR indicates that a marked and widespread breakdown of intracortical effective connectivity emerges after sleep onset and becomes fully pronounced in deeper sleep stages.

13:15 Marcin Iwański

Third Department of Psychiatry, Affective Disorders Unit and Sleep Medicine Centre, Institute of Psychiatry and Neurology

"Phenotyping Delayed Sleep-Wake Phase Disorder through Integration of DLMO Timing, Phase Angle, and Pupillometry"

Circadian rhythm sleep–wake disorders are a group of sleep disorders. The most prevalent diagnosis within this group is delayed sleep–wake phase disorder (DSWPD). It has been proposed that DSWPD may be subdivided into two phenotypes: chronobiological and behavioral. The chronobiological phenotype is characterized by a delayed dim light melatonin onset (DLMO) in relation to the desired sleep onset, whereas the behavioral phenotype does not exhibit such a delay. DLMO delay is caused by light exposure of retinal ganglion cells.

The objectives of the study were to identify a pupillometry screening protocol for the diagnosis of DSWPD, to utilize DLMO for phenotyping DSWPD, and to evaluate retinal ganglion cell light sensitivity as a risk factor for the development of chronobiological DSWPD.

We conducted a study evaluating salivary DLMO and retinal ganglion cell light sensitivity using pupillometry, a method that measures parameters of the pupillary light reflex.

Achieving these objectives will enable us to develop targeted therapeutic programs for patients with chronobiological or behavioral DSWPD.

13:30 Michal Rafal Zareba

Jaume I University, Department of Basic and Clinical Psychology and Psychobiology, Castellon de la Plana, Spain

"Opposing Diurnal Trajectories of Dopamine D2 and MU-opiod Receptor Availability and Their Seasonal Modulation in the Human Brain"

Diurnal variability in arousal, motivation and cognitive performance are known to be modulated by seasonal differences in light exposure, with the intricate connections between these phenomena being especially evident in seasonal affective disorder.

Considering the role of the dopaminergic and opioidergic systems in the aforementioned cognitive processes, the current work used a large positron emission tomography (PET) dataset (n = 377) to explore the presence of time-of-day (TOD)-dependent fluctuations in receptor availability, considering the previously reported effects of seasonality and subclinical anxiety.

The data revealed decreased dopamine type-2 (D2R) and increased mu-opioid receptor (MOR) availability in the afternoon compared to morning. The impact of the interactions with the seasonal daylength changes was, however, observed only for MOR, mapping onto brain networks implicated in emotion processing, affective regulation and social cognition. Interestingly, the MOR availability in the aforementioned regions was also sensitive to the interactions of TOD and individual anxiety levels.

As such, the current results reveal the diurnal variability in indices of dopaminergic and opioidergic neurotransmission by highlighting the opposing trajectory between the two systems. Furthermore, the data pinpoints the special role that the opioid system may play in linking together diurnal and seasonal rhythms with affective and anxiety disorders.