Figure 2.

fNIRS-based brain measures of acute and/or ongoing pain measured during the various perioperative states. The measured brain states at each perioperative stage can be both intrinsic and extrinsic. Intrinsic brain state often refers to the brain in the absence of external stimuli, such as during persistent ongoing pain. In contrast, extrinsic brain state refers to the brain during an acute stimulus, intervention, or treatment.