However, pain is not purely a sensory event but is also reflective of how the person feels about their pain. Factors that vary widely across a population such as memories, emotion, pathology, genetics, and cognitive factors all directly affect how an individual experiences pain. In addition, the way a person responds to pain is modified heavily by what is appropriate for the situation. For example, a person in pain may hide how unpleasant the sensation is if they are uncomfortable in their surroundings. Because of this, the pain matrix provides an incomplete picture of what is happening in the brain during pain. Pain imaging studies have begun to validate this perspective. For example, Derbyshire and collaborators showed activation of the key pain matrix regions even when subjects were not in pain. From a study looking at chronic pain sufferers, it was shown that a series of other key brain regions were active that were outside the pain matrix. It is essential for brain imaging research to update the notion of the 'pain matrix' to account for these inconsistencies.