The neural correlates of arousal: Ventral posterolateral nucleus-global transient co-activation.

Arousal and awareness are two components of consciousness whose neural mechanisms remain unclear. Spontaneous peaks of global (brain-wide) blood-oxygenation-level-dependent (BOLD) signal have been found to be sensitive to changes in arousal. By contrasting BOLD signals at different arousal levels, we find decreased activation of the ventral posterolateral nucleus (VPL) during transient peaks in the global signal in low arousal and awareness states (non-rapid eye movement sleep and anesthesia) compared to wakefulness and in eyes-closed compared to eyes-open conditions in healthy awake individuals. Intriguingly, VPL-global co-activation remains high in patients with unresponsive wakefulness syndrome (UWS), who exhibit high arousal without awareness, while it reduces in rapid eye movement sleep, a state characterized by low arousal but high awareness. Furthermore, lower co-activation is found in individuals during N3 sleep compared to patients with UWS. These results demonstrate that co-activation of VPL and global activity is critical to arousal but not to awareness. [Display omitted] • Co-activation of VPL and global brain is elevated in wakefulness and unresponsive wakefulness • VPL activity is reduced in low arousal states compared to global brain activity • Co-activation of VPL and global transient signal is related to arousal rather than awareness • VPL might attain co-activation with global cortex via sensory-motor areas to modulate arousal Han et al. employed multi-center fMRI data to dissociate the components of consciousness, arousal, and awareness. By comparing co-activation of spontaneous global brain signal across conditions, they demonstrate that transient co-activation of the ventral posterolateral nucleus and global signal is predominantly associated with arousal rather than awareness. [ABSTRACT FROM AUTHOR]