Scale-free physiological processes are common in the human body. Resting-state fMRI studies found that anesthesia eliminates scale-free dynamics. This study examines scale-free dynamics in the cerebral cortex's unimodal periphery and transmodal core during rest and tasks at three conscious levels (awake, sedation, anesthesia), complemented by computational modeling. The results show that anesthesia transforms pink noise into white noise, disrupting the brain's alignment with a task's temporal structure. The model indicates that stimuli with pink noise, unlike brown or white noise, modulate task-related activity. The findings support two mechanisms of consciousness—temporo-spatial nestedness and alignment—proposed by the Temporo-Spatial Theory of Consciousness.
Consciousness has a structure with foreground contents and a background environment, a relation that depends on the brain's interaction with the body and external world. The temporo-spatial theory proposes that the brain aligns its neuronal activity to environmental stimuli across three layers: a background layer with longer timescales creating shared brain similarities across subjects, an intermediate layer with medium timescales matching environmental inputs to intrinsic neuronal rhythms, and a foreground layer with shorter timescales entraining to stimulus timing. These layers correspond to phenomenal layers: a shared contextual background, a layer mediating content relationships, and fast-changing specific contents. This alignment may bridge physical, dynamic, neuronal, and phenomenal mechanisms of consciousness.