Sleep stages affect low-gamma range effective cortical connectivity for 40-Hz auditory steady-state responses

Area of Science:

• Neuroscience
• Sleep Research
• Auditory Neuroscience

Background:

• The 40-Hz auditory steady-state response (40-Hz ASSR) reflects arousal levels and decreases during sleep.
• Understanding how sleep stages affect the directional brain connectivity underlying 40-Hz ASSR is crucial but remains unclear.

Purpose of the Study:

• To investigate how wakefulness and sleep stages (NREM N1, N2, N3, REM) alter the direction and extent of cortical signal propagation during 40-Hz ASSR.
• To test hypotheses regarding impaired feedback connections and progressive associative connectivity decline across sleep stages.

Main Methods:

• Overnight EEG recording during 40-Hz auditory stimulation in 29 healthy adults.
• Source reconstruction to identify cortical generators.
• Quantification of effective connectivity using Directed Transfer Function (DTF) in the low-gamma band (37-43Hz) between auditory, prefrontal, and temporo-parietal regions.

Main Results:

• Both feedforward and feedback connectivity were reduced comparably during NREM (N2, N3) and REM sleep.
• At sleep onset (N1), feedforward disruptions were significant but localized, while feedback reductions were less pronounced initially, increasing with sleep depth.
• Associative connectivity between prefrontal and temporo-parietal cortices decreased with increasing sleep depth, confirming a key hypothesis.

Conclusions:

• Sleep onset is characterized by a breakdown in feedforward auditory signal processing.
• A progressive decline in feedback and associative cortico-cortical connectivity occurs with increasing sleep depth.
• Overall, sleep leads to a widespread disruption of intracortical effective connectivity underlying the 40-Hz ASSR.