Unravelling the link between chronic pain and mental health disorders
Chronic pain is a significant problem worldwide that results in enormous suffering and costs to affected individuals, their loved ones, and society. The experience of chronic pain is so much more than a sensation. Chronic pain impacts our emotions, cognition and social life. In Australia, an alarming 20 per cent of people with chronic pain have considered suicide.
NeuRA’s Dr Sylivia Gustin and her team are at the forefront of unravelling the impact of chronic pain on the brain. People with chronic pain can develop mental health disorders including anxiety and depression. The prevalence of depression in people with chronic pain is as high as 54 per cent and at least 35 per cent experience anxiety.
The medial prefrontal cortex (mPFC) which sits just behind the forehead is of particular interest when considering emotional and cognitive processing in the brain. The mPFC is especially vulnerable to the effects of stress. Brooke Naylor, from NeuRA’s Pain Imaging Laboratory led by Dr Gustin, showed that people with chronic pain have a decrease in glutamate, within the mPFC, which is the main excitatory neurotransmitter in the central nervous system. The decrease in mPFC glutamate is associated with excessive worry, pessimism, fear and doubt.
David Kang from the Pain Imaging Laboratory revealed that people with chronic pain also have a decrease in GABA, within the mPFC, the central nervous system’s main inhibitory neurotransmitter. The decrease in mPFC GABA is critical in the development and maintenance of depression.
Research by Anton Paulson from the Pain Imaging Laboratory, has also shown that people with chronic pain have increased activity, e.g. blood flow, in the mPFC compared to people without pain.
In summary, the research from the Pain Imaging Team supports a hyperexcitability hypothesis of chronic pain that is underpinned by glutamatergic/GABAergic imbalance. This means that the mPFC has lost its ability to dampen down pessimistic and/or fearful thoughts and emotions resulting in anxiety or depression.
Daniel Hultberg, also a member of the Pain Imaging team, has shown that the connection between the mPFC and the hippocampus, which is critical in learning and memory, is disrupted. This means that emotional and cognitive learning and memory in people with chronic pain may be maladaptive, resulting in learned worry, pessimism, fear and doubt.
Given the urgent need of novel effective pain therapies for the millions of people affected by chronic pain worldwide, the research that Dr Gustin and her team are doing is fundamental to understanding the underlying mechanisms for the development and maintenance of chronic pain and comorbid mental health disorders so that more effective treatments can be developed.