Low frequency BOLD fluctuations during resting wakefulness and light sleep: a simultaneous EEG-fMRI study

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neuroimaging

Background:

• Spontaneous brain activity, characterized by temporally correlated signal fluctuations, is observable via blood oxygenation level dependent functional MRI (BOLD fMRI) even without external stimuli.
• Understanding the persistence of these BOLD fMRI fluctuations during altered states of consciousness is crucial for mapping brain function.

Purpose of the Study:

• To investigate spontaneous BOLD fMRI signal fluctuations during varying levels of consciousness, specifically drowsiness and light sleep.
• To determine if default-mode network (DMN) and primary sensory cortex activity, as measured by BOLD fMRI, are maintained during reduced consciousness.

Main Methods:

• BOLD fMRI was performed on normal subjects across a spectrum of consciousness levels, from resting wakefulness to light non-slow wave sleep.
• Electroencephalography (EEG) was concurrently acquired to precisely determine the depth of sleep.

Main Results:

• A significant increase in BOLD signal fluctuation levels was observed in multiple cortical areas during light sleep, with the visual cortex showing the most pronounced effect.
• Correlations within the default-mode network remained persistent during light sleep.
• Increased BOLD signal fluctuations were noted in the primary sensory cortex during light sleep.

Conclusions:

• Spontaneous BOLD fMRI activity in areas like the default-mode network and primary sensory cortex persists during light sleep.
• These findings suggest that a state of wakefulness is not a prerequisite for measurable activity in these key brain networks.
• BOLD fMRI is a valuable tool for studying brain function during altered states of consciousness.