The advent of functional imaging techniques allowed researchers to begin to look within the human brain to observe what pain looks like in the brain. Initially, pain imaging research determined that pain is not processed by a single brain region but instead engages several distributed cortical areas. The group of brain regions that are most active during pain are commonly referred to as the 'pain matrix'. This includes: primary and secondary somatosensory cortices (SI, SII), insular, anterior cingulate, and prefrontal cortices and the thalamus.