There are several features that characterize emotions and are given different weights in theories of emotions. Emotions are triggered by objects or events that are immediately present or evoked mentally. Functional imaging of pain in humans is based firmly on the fundamental knowledge acquired in animal studies on the transmission and integration of noxious information at multiple levels of the central nervous system (CNS). The relative neurofunctional specificity of pain processes may be found at the level of the neural networks within each area that are activated by painful stimuli and reflect the underlying factors that make pain highly salient based on its strong intensity and inherent affective valence. Acute pain is generally accompanied by a robust autonomic activation. The analysis of neurophysiological activity underlying nociception and pain must consider the multiple responses that accompany painful experiences and are not necessarily encoded adequately in subjective responses.