BRAIN CORRELATES OF PAIN REALITY†
Suggestion-induced pain activates brainís pain circuitry as well as a real pain experience. These two mind states correspond to different degrees of conscious reality. Recently Tuukka T. Raij et al. (Brain correlates of subjective reality of physically and psychologically induced pain. Proc. Natl. Acad. Sci. USA 10.1073/pnas 0409542102 published on-line before print, January 31 2005) investigated the neurological basis of such a difference.
Meaningful behaviour requires successful differentiation of events surfacing oneís mind from those arising from the external world. Such judgements may be especially demanding during pain because of the strong contribution from psychological factors to this experience. It is unknown how the subjective reality of pain (SRP) is constructed in the human brain, and neuronal mechanisms of the subjective reality are poorly understood in general.
To address these questions, 14 suggestion-prone healthy subjects rated reality of pain that was induced either by laser pulses to the skin or by hypnotic suggestion during functional MRI. Both pain states were associated with activation of the brainís pain circuitry. During laser stimulation, the sensory parts of this circuitry were activated more strongly, and their activation strengths correlated positively with the SRP. During suggestion-induced pain, the reality estimates were lower and correlated positively with activation strengths in the rostral and perigenual anterior cingulate cortex and in the pericingulate regions of the medial prefrontal cortex; a similar trend was evident during laser-induced pain. These findings support the view that information about sensory-discriminative characteristics of pain contributes to the SRP.
Differences in such information between physically and psychologically induced pain, however, could be quantitative rather than qualitative and therefore insufficient for judging the reality of pain without knowledge about the source of this information. The medial prefrontal cortex is a likely area to contribute to such source monitoring.