For chronic pain sufferers, such as people who develop back pain after a car accident, avoiding the harmful effects of stress may be key to managing their condition.

 
This is particularly important for people with a smaller-than-average hippocampus, as these individuals seem to be particularly vulnerable to stress. These are the findings of a study by Dr. Pierre Rainville, PhD in Neuropsychology, Researcher at the Research Centre of the Institut universitaire de gériatrie de Montréal (IUGM) and Professor in the Faculty of Dentistry at Université de Montréal, along with Étienne Vachon-Presseau, a PhD student in Neuropsychology. The study appeared in Brain, a journal published by Oxford University Press.

“Cortisol, a hormone produced by the adrenal glands, is sometimes called the ‘stress hormone’ as it is activated in reaction to stress. Our study shows that a small hippocampal volume is associated with higher cortisol levels, which lead to increased vulnerability to pain and could increase the risk of developing pain chronicity,” explained Étienne Vachon-Presseau.

As Dr. Pierre Rainville described, “Our research sheds more light on the neurobiological mechanisms of this important relationship between stress and pain. Whether the result of an accident, illness or surgery, pain is often associated with high levels of stress Our findings are useful in that they open up avenues for people who suffer from pain to find treatments that may decrease its impact and perhaps even prevent chronicity. To complement their medical treatment, pain sufferers can also work on their stress management and fear of pain by getting help from a psychologist and trying relaxation or meditation techniques.”

Research summary

This study included 16 patients with chronic back pain and a control group of 18 healthy subjects. The goal was to analyze the relationships between four factors: 1) cortisol levels, which were determined with saliva samples; 2) the assessment of clinical pain reported by patients prior to their brain scan (self-perception of pain); 3) hippocampal volumes measured with anatomical magnetic resonance imaging (MRI); and 4) brain activations assessed with functional MRI (fMRI) following thermal pain stimulations. The results showed that patients with chronic pain generally have higher cortisol levels than healthy individuals.

Data analysis revealed that patients with a smaller hippocampus have higher cortisol levels and stronger responses to acute pain in a brain region involved in anticipatory anxiety in relation to pain. The response of the brain to the painful procedure during the scan partly reflected the intensity of the patient’s current clinical pain condition. These findings support the chronic pain vulnerability model in which people with a smaller hippocampus develop a stronger stress response, which in turn increases their pain and perhaps their risk of suffering from chronic pain. This study also supports stress management interventions as a treatment option for chronic pain sufferers.

Source: University of Montreal
Étienne Vachon-Presseau, Mathieu Roy, Marc-Olivier Martel, Etienne Caron, Marie-France Marin, Jeni Chen, Geneviève Albouy, Isabelle Plante, Michael J. Sullivan, Sonia J. Lupien et Pierre Rainville. “The stress model of chronic pain: evidence from basal cortisol and hippocampal structure and function in humans”, February 18, 2013, BRAIN.

ᔥNorthwestern University

When people have similar injuries, why do some end up with chronic pain while others recover and are pain free? The first longitudinal brain imaging study to track participants with a new back injury has found the chronic pain is all in their heads –- quite literally.

A new Northwestern Medicine study shows for the first time that chronic pain develops the more two sections of the brain — related to emotional and motivational behavior — talk to each other. The more they communicate, the greater the chance a patient will develop chronic pain.

The finding provides a new direction for developing therapies to treat intractable pain, which affects 30 to 40 million adults in the United States.

Researchers were able to predict, with 85 percent accuracy at the beginning of the study, which participants would go on to develop chronic pain based on the level of interaction between the frontal cortex and the nucleus accumbens.

The study is published in the journal Nature Neuroscience.

“For the first time we can explain why people who may have the exact same initial pain either go on to recover or develop chronic pain,” said A. Vania Apakarian, senior author of the paper and professor of physiology at Northwestern University Feinberg School of Medicine.

“The injury by itself is not enough to explain the ongoing pain. It has to do with the injury combined with the state of the brain. This finding is the culmination of 10 years of our research.”

The more emotionally the brain reacts to the initial injury, the more likely the pain will persist after the injury has healed. “It may be that these sections of the brain are more excited to begin with in certain individuals, or there may be genetic and environmental influences that predispose these brain regions to interact at an excitable level,” Apkarian said.

The nucleus accumbens is an important center for teaching the rest of the brain how to evaluate and react to the outside world, Apkarian noted, and this brain region may use the pain signal to teach the rest of the brain to develop chronic pain.

“Now we hope to develop new therapies for treatment based on this finding,” Apkarian added.

Chronic pain participants in the study also lost gray matter density, which is likely linked to fewer synaptic connections or neuronal and glial shrinkage, Apkarian said. Brain synapses are essential for communication between neurons.

“Chronic pain is one of the most expensive health care conditions in the U. S. yet there still is not a scientifically validated therapy for this condition,” Apkarian said. Chronic pain costs an estimated $600 billion a year, according to a 2011 National Academy of Sciences report. Back pain is the most prevalent chronic pain condition.

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