Brain Mechanisms of Persistent Pain States

SUMMARY

Objectives: The objective of this review is to explain the relationships between neural mechanisms of persistent pain and neural representations of these conditions in brains of animal models and in brains of human pain patients.

Findings: Animal models of persistent pain, such as that which results from constrictive injury to the sciatic nerve or from intradermal injections of formalin, are accompanied by spatially widespread yet somatotopically organized increases in spinal cord dorsal horn neural activity and by similar widespread somatotopically organized increases in several pain-related areas of the brain. Consistent with these animal studies, human brain imaging studies that examine neural representations of visceral and cutaneous hyperalgesia have found that both forms of hyperalgesia are represented in many of the same multiple brain regions that are activated during acute normal pain, yet have a more extensive representation.

Conclusions: Hyperalgesic states are represented by increased activity in the same pathways and centers that are involved in acute normal pain. Additional areas activated during clinically relevant pain include prefrontal cortical regions, possibly in association with psychological factors that are prevalent in clinical pain [e.g., anxiety, fear, depression, frustration].

KEYWORDS:

• Persistent pain
• cutaneous and visceral hyperalgesia
• brain imaging