Fig. 2.

Brain mechanisms of opioid analgesia. Pain perception is generated by neural activation in the inter-connected (light-grey arrows) brain regions that have sensory-discriminatory (blue) and affective-motivational (red) functions. Opioids may alter the consciousness of pain directly by preferential targeting of limbic regions (in red box). Additionally, opioids may engage limbic-brainstem inhibition of spinal nociception (dark grey arrows), which also occurs during cognitive control of pain that involves the prefrontal cortex (PFC).