5.42 - Emotional and Behavioral Significance of the Pain Signal and the Role of the Midbrain Periaqueductal Gray (PAG)

Abstract

Humans and animals react with distinct emotional coping strategies to pain of different durations or different tissue origins. Active coping strategies (fight or flight) are evoked if pain is cutaneous and of short duration (i.e., escapable). In contrast, acute pain of deep origin (muscle, joint, viscera) or any persistent pain evokes usually a passive emotional coping reaction (conservation-withdrawal). Distinct longitudinal neuronal columns within the periaqueductal gray (PAG) mediate active versus passive emotional coping. Anatomical tracing studies reveal that each PAG column receives a distinct set of ascending (spinal cord, medulla) and descending (prefrontal cortical, hypothalamus) afferents. Functional studies, using immediate early gene expression as a marker of neuronal activation indicate further that each PAG neuronal column is activated in a manner which reflects (1) the tissue origin and or duration of pain; (2) the escapability of the stimulus; and (3) the emotional coping reaction engaged.