Breakdown of Cortical Effective Connectivity During Sleep

TLDR

Sleep causes consciousness to fade while the brain remains active, raising questions about the underlying mechanisms. The study aimed to determine whether altered cortical information transmission underlies consciousness loss during sleep by stimulating the premotor area and recording responses. Transcranial magnetic stimulation and high‑density EEG were employed to map the propagation of premotor activation across cortical networks. In quiet wakefulness, premotor stimulation produced a rapid (~15 ms) response that propagated to distant cortical areas, whereas during NREM sleep the response was stronger but quickly extinguished and failed to spread beyond the stimulation site, indicating a breakdown of effective connectivity.

Abstract

When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (∼15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non–rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.