Common Neural Correlates for Subjective and Objective Sleepiness Indices: A Functional Connectivity Study

Area of Science:

• Neuroscience
• Sleep Science
• Cognitive Neuroscience

Background:

• Subjective and objective measures of sleepiness, like the Karolinska Sleepiness Scale (KSS) and Psychomotor Vigilance Task (PVT), are crucial for understanding sleep debt.
• Functional brain connectivity offers a method to explore common neural substrates underlying different states of arousal.
• Identifying shared neural mechanisms can lead to more robust markers for sleepiness.

Purpose of the Study:

• To investigate the neural correlates of functional brain connectivity common to both subjective and objective sleepiness.
• To explore commonalities in brain connectivity during rest and task performance (PVT) using fMRI.
• To identify robust neural markers for sleepiness that are independent of task demands.

Main Methods:

• 16 healthy adult men participated in a 14-day study involving extended sleep, total sleep deprivation, and recovery sleep.
• Subjective sleepiness was assessed using the Karolinska Sleepiness Scale (KSS), and objective sleepiness using the Psychomotor Vigilance Task (PVT).
• Resting-state and task-based functional magnetic resonance imaging (fMRI) were used to measure brain connectivity, analyzed with a general linear mixed model.

Main Results:

• Functional connectivity in six pairs of brain regions, including the anterior cingulate cortex-posterior cingulate cortex and thalamus-middle temporal cortex, was significantly associated with sleepiness.
• Connectivity within the default mode network (anterior cingulate cortex-posterior cingulate cortex) showed a strong link to sleepiness.
• The thalamus-middle temporal cortex connection emerged as a potentially novel network related to sleepiness.

Conclusions:

• The study suggests a common neural substrate for subjective and objective sleepiness, providing important indicators for sleepiness.
• The identified functional connectivity between the thalamus and middle temporal cortex warrants further investigation in sleep research.
• The findings offer new perspectives on how sleep deprivation affects the brain and manifests as sleepiness.