 Monitoring pain during modern surgery might seem like a strange concept. The point of general anesthesia is, after all, to block pain signals to our brains. But the problem is that it doesn't, not completely anyway. Nociceptors, the receptors from which pain signals originate, often remain active during surgery, and in some cases, can remain abnormally active afterward, leading to chronic pain in patients' post-surgery. That's why pain monitoring is critical. Unfortunately, there is no standard method for quantifying nociceptive pain during anesthesia. A new study published in the journal Anesthesiology reports on one promising imaging technique that might be integrated into the common operating room. The method relies on a technology called functional near-infrared spectroscopy, or F-nears. F-nears captures changes in blood oxygen that researchers know from functional MRI studies correlate with nociceptive pain signaling. But whereas F-MRI restricts patient position and motion, F-nears is portable and can be applied more easily during surgery. Researchers tested F-nears on two groups of patients, healthy volunteers who remained awake throughout the study, and patients undergoing routine general anesthesia for surgery. The goal was to compare pain-related F-nears patterns between the two groups. The team predicted that stimulating pain in the awake volunteers using heat would produce changes in blood oxygen, similar to those observed in patients undergoing surgery. Experiments revealed a decrease in low-frequency F-nears signals in the awake group when exposed to pain-stimulating heat. A similar decrease was observed among patients undergoing surgery, suggesting that F-nears could communicate active nociceptive pain signaling. What's more, that pain signaling could actually be altered externally. In addition to general anesthesia, some patients undergoing surgery received regional anesthesia to block pain signaling to the brain. Patients receiving regional anesthesia showed diminished or no changes in their F-nears patterns. This finding suggests that, in addition to making otherwise hidden pain signals visible during surgery, clinicians might also be able to control that signaling to some extent. More work is needed before F-nears becomes a trusted part of the surgeon and anesthesiologist toolkit. It remains unclear, for example, the extent to which pain signals can be differentiated from the body's other physiological responses. Further testing could help improve the sensitivity and specificity of F-nears for patients undergoing surgery and provide ways of measuring and controlling nociceptive pain in real time.