Early Experience of Pain has Lasting Effects

Lessened pain sensitivity, lack of coping strategies and poor cognitive development are some of the consequences researchers are studying.

About 9,000 newborn infants are receiving intensive care in the U.S. today, and many will be exposed to medical procedures that cause pain, such as needle sticks and circumcisions. Babies often receive less pain-relieving medicine before invasive procedures or after surgery than adults do. An inflammatory response lasting from hours to days will follow, leading to increased pain sensitivity around the damaged tissue. In the past, this also went untreated, primarily due to the mistaken belief that 'babies don't perceive or remember painful experiences.'

Medical researchers and the general public are keenly interested in the effects of early pain experiences on brain development and whether such experiences affect pain perception and behavior in adulthood.

Cutting-edge research by University of Tennessee Health Science Center neuroscientists on the consequences of neonatal pain will be the topic of a public symposium at on March 24.

Among the topics we will discuss at the symposium is the earliest perception of pain and consciousness in human infants. Research demonstrates that human infants perceive pain, as determined by physiological and behavioral responses, at their earliest developmental stages, even before birth.

A critically important question is: What are the lasting consequences of the early experience of pain? Emerging evidence indicates that neonatal pain can have profound and perhaps permanent effects on development. For example, premature babies receiving painful clinical procedures during intensive care later exhibited a lower reaction to pain. In fact, there was a strong correlation between the number of painful procedures and the resulting reduction in pain sensitivity.

At the March 24 event we will discuss animal research that shows that experience of pain during an early stage of development known as the 'sensitive or critical period' permanently alters pain perception in the adult in a manner remarkably similar to that in humans. These studies further show that pain during the critical period permanently changes the way neural pathways and circuits in the brain are organized.

Such studies have only scratched the surface as the human brain is bewilderingly complex, with 100 billion cells, each with 7,000 to 10,000 connections. Further research using modern techniques to map and visualize neurons and their connections will be needed to reveal all the effects of neonatal pain on the brain and behavior.

Taken together, converging human and animal studies demonstrate that painful experiences in early life may leave a legacy of altered sensitivity to subsequent pain. One of the consequences that has been observed is a lowered sensitivity to pain in later life. Intuitively, one might think this is beneficial. However, this may not be the case because pain serves to warn and protect a person against further injury. In addition to changes in pain perception, lack of coping strategies, psychosocial problems and poor cognitive development continue to plague these children throughout their childhood, often leading to abnormal behaviors in adult life.

A major question in clinical studies and in the treatment of infants is whether such changes require conscious sensory perception of pain in the neonate. The symposium will include a discussion of clinical work that indicates that pain and consciousness may be inextricably linked. During anesthesia, pain is the last sensation lost before we become unconscious. On regaining consciousness, pain is the first sensation that we become aware of, much before sight, sound or smell are regained. If pain and consciousness occur so closely together, could they be linked and possibly converge in common brain areas? These intriguing questions will be explored in the symposium.

Findings from laboratory and clinical studies highlight the fact that early painful experiences will be 'remembered' by the developing brain, perhaps for the entire life of the individual. This work has also led to increased awareness by pediatricians, health care providers and the public that newborns are sensitive to pain at the earliest stages of development. Within the medical arena, these discoveries will stimulate the development of better anesthetic approaches for fetal surgery, ways of preventing pain in premature babies or easing the pain of immunization in infants.

By K.J.S. Anand and Matthew Ennis, Special to Viewpoint

K.J.S. Anand is division chief of Pediatric Critical Care Medicine at Le Bonheur Children's Hospital. Matthew Ennis is chairman of the Department of Anatomy and Neurobiology at the University of Tennessee Health Science Center.

The symposium featuring Dr. Anand and Dr. Ennis will begin at 6:30 p.m. on March 24 at The Urban Child Institute at 600 Jefferson. A reception will be held from 5:30 p.m. to 6:30 p.m.; RSVP to scook@tuci.org.

This is one in a series of monthly guest columns on the importance of public/private investment in early childhood. For more information, call The Urban Child Institute at 385-4233.

Originally appeared in The Commercial Appeal at http://www.commercialappeal.com/news/2011/mar/12/guest-column-early-experience-of-pain-has