Diurnal variations of resting-state fMRI data: A graph-based analysis

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Chronobiology

Background:

• Circadian rhythms influence physiological processes, including cognitive functions.
• Time of day (TOD) is known to affect human cognition and brain activity.
• Understanding diurnal variations in brain function is crucial for research and experimental design.

Purpose of the Study:

• To investigate the impact of time of day and chronotype on whole-brain functional network topology using resting-state functional MRI (rs-fMRI).
• To compare functional connectivity (FC) patterns between morning and evening sessions and between morning-type (MT) and evening-type (ET) individuals.

Main Methods:

• Utilized a graph theory approach on rs-fMRI data from 62 participants (31 MT, 31 ET).
• Conducted two fMRI sessions: one in the morning and one in the evening, relative to wake-up time.
• Analyzed global, mesoscale (modular), and local/regional network properties.

Main Results:

• Global analysis revealed increased small-worldness, assortativity, and synchronization across the day, indicating TOD effects on FC.
• Functional networks showed greater integration in the evening compared to the morning session.
• Local/regional changes were influenced by both TOD and chronotype, particularly in somatomotor, attention, frontoparietal, and default networks.
• Somatomotor network hubs were more active in the evening, while ventral attention and visual networks were more active in the morning.

Conclusions:

• Time of day significantly modulates resting-state brain activity and functional network topology.
• While chronotype did not significantly alter global network topology, TOD influences both global and local brain network organization.
• Findings underscore the importance of considering diurnal fluctuations in brain function for future neuroimaging studies and experimental designs.