Numerous studies involving functional magnetic resonance imaging (fMRI) of the brain, tell us that chronic back pain (CBP) alters brain function well beyond the feeling of pain and can cause impairments like depression, impaired decision-making and sleep disturbance [1,2].
It was Baliki’s group in 2008 which confirmed for the first time that CBP disrupts the dynamics of the default-mode network (DMN) of the brain [2]. From now on the default mode network or DMN is to be known as DAMIEN because that is easy to remember. The DAMIEN is a network of four cortical regions normally more active at rest than during performance of tasks; it’s what lights up when we are in our resting state.
In this current study Tagliazucchi and colleagues are investigating whether or not the spontaneous activity in resting state networks (RSNs) demonstrates the alterations in DAMIEN that Baliki and friends found earlier. Basically there are several well-established resting state networks; their functional connectivity has already been studied [3]. The authors of this paper looked at eight of them, of which DAMIEN is one—he’s the fifth one.
fMRI data were acquired from CBP patients and healthy controls as they lay still in an MRI scanner, keeping their eyes closed and minds ‘blank’. (I’m not sure how the latter was achieved. If it were me I would have had to devote much thought and attention to not thinking about anything.)
A lot of this paper is very technical, outlining the specific method by which ‘hubs’—the most functionally connected sites of each resting state network— were identified, and then tested for validity with extra control participants.
All in all, the team found increased activity in three of four sites belonging to DAMIEN, when CBP subjects were compared to healthy controls. The middle frontal gyrus and the left and right angular gyri showed significant increases in correlation with the insular cortex in CBP subjects. So, CBP sufferers were found to exhibit significant spontaneous co-activation between these sites and the insula; in normals there was close to zero co-activation in all three DAMIEN sites.
There were significant decreases in correlation between these three areas and parts of the middle frontal gyrus in the CBP group.
The team interprets the following: that long term pain alters brain connectivity. This is reflected in spontaneous fluctuations in brain activity.
Why is it of interest to us that a correlation was found between DAMIEN sites and the insular cortex? Because there are data already on the insular cortex being involved in the evaluation of pain and in interoception, the awareness of the internal state of our own bodies [4]. And why should we be bothered about a decreased correlation between Damien and the middle frontal gyrus? Well the middle frontal gyrus is situated in the resting state network where executive control is carried out; an area found to be functionally specialised for decision making [1, 2]. This makes sense when we think about some of the cognitive issues we see in so many CBP patients.
So…thanks to the authors of this paper, Baliki and friends, and of course DAMIEN himself, some of the neuroscience behind the cognitive impairments that we often see in chronic back pain sufferers is explained.
About Flavia
Flavia Di Pietro is a PhD student in the Moseley Group investigating the development of Complex Regional Pain Syndrome (CRPS) after wrist fracture. Flavia’s PhD focuses on the early detection of brain changes in CRPS using fMRI. But get this – Flavia did Physiotherapy Honours degree at Notre Dame and completely cleaned up – Brian Edwards Memorial Award, Physio Research Foundation Award, Dean’s Award. Now, these things mean that she is not only ticking the academic boxes but all the other fluffy stuff too. No surprises that the NHMRC of Australia jumped to support her PhD. So she has come over from Perth where she has been working as a physiotherapist. All her achievements, however, pale in comparison to her celebrated status as the best Shoe Salesperson south of Milano, as evidenced by her taking out the 2006 and 2008 Diana Ferrari Golden Boot Award. Clearly, she did not write this bio.
* One of the awards in Flavia’s bio is fictitious.
References
[1] Apkarian AV, Sosa Y, Krauss BR, Thomas PS, Fredrickson BE, Levy RE, Harden RN, & Chialvo DR (2004). Chronic pain patients are impaired on an emotional decision-making task. Pain, 108 (1-2), 129-36 PMID: 15109516
[2] Baliki MN, Geha PY, Apkarian AV, & Chialvo DR (2008). Beyond feeling: chronic pain hurts the brain, disrupting the default-mode network dynamics. J Neurosci, 28 (6), 1398-403 PMID: 18256259
[3] Beckmann, C., DeLuca, M., Devlin, J., & Smith, S. (2005). Investigations into resting-state connectivity using independent component analysis Phil Trans R Soc B, 360 (1457), 1001-1013 DOI: 10.1098/rstb.2005.1634
[4] Craig AD (2009). How do you feel–now? The anterior insula and human awareness. Nature reviews. Neuroscience, 10 (1), 59-70 PMID: 19096369