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Dr Ben Seymour, Computational and Biological Learning Lab, Trumpington Street, Cambridge CB2 1PZ

and

Center for Information and Neural Networks, National Institute for Information and Communications Technology (NICT), 1-3 Yamadaoka, Suita, Osaka 565-0871, Japan.

bjs49 AT cam.ac.uk / seymour AT cinet.jp

F1000 reviews (paywall)

 

Thursday
Feb022012

The cortical rhythms of chronic back pain

It seems increasingly unlikely that we are going to understand chronic pain as the isolated overactivity of a single brain region, and much more likely that it relates to the abnormal dynamic activity and connectivity between a network that spans cortical, subcortical and spinal regions. But finding out the nature of this abnormal connectivity is not an easy task. This study focuses on one such method: resting frequency analysis of the functional magnetic resonance imaging (fMRI) blood-oxygen-level-dependent (BOLD) signal. Not only do the authors show clear excess of high-frequency oscillatory activity in patients, centred on medial prefrontal cortical activity, but they also show that this abnormal activity correlates with spontaneous fluctuations of pain, providing the first convincing evidence of a functional relationship between dynamic cortical activity and chronic pain.

This is likely to stimulate research into sophisticated spatiotemporal decoding methods for fMRI activity, as well as parallel studies using other methodologies (such as magnetoencephalography [MEG]), and marks an important direction for chronic pain research.

Baliki MN, Baria AT, Apkarian AV. The cortical rhythms of chronic back pain. J Neurosci. 2011 Sep 28; 31(39): 13981-90

Tuesday
Jan312012

Distracted by placebo

Buhle and colleagues' recentlyn pblished a extremely interesting paper -- they convincingly show that placebo-related analgesia and working memory 'load'-associated analgesia show no interaction, suggesting that they represent different mechanisms. This is important for our understanding of pain, and the result is one that is not obvious and will change the way many view endogenous analgesia. The strength of what is ultimately a negative finding (i.e. lack of an interaction) results from the adequacy of the design and analysis, and the strength of the main effects.

Buhle JT, Stevens BL, Friedman JJ, Wager TD. Distraction and placebo: two separate routes to pain control. Psychol Sci. 2012 Mar 1; 23(3): 246-53

Wednesday
Jan112012

The puzzle of the putamen and pain.

Here's an extremely interesting study on the functional role of the putamen in pain processing - 'The contribution of the putamen to sensory aspects of pain: insights from structural connectivity and brain' by Starr and colleagues {1}.

The results are subtle. The extent to which it shows a role of the putamen in core sensory processing of pain is an interesting question. Consideration of the functional role of the putamen in behaviour in general suggests several possible mechanisms by which pain processing might be disrupted. First, we know the putamen plays a central role in dopamine-dependent reward value learning, and we know dopamine boosts sensory perceptual learning (e.g. improvements in tactile discrimination learning over time) {2}. Thus, perhaps the deficit here relates to a failure to improve performance in response to the task goal (which is by definition a reward). It would be interesting to know how performance changed over the course of the experiment. 

Second, we also know the ventral putamen is involved in pain (aversive) value learning from functional magnetic resonance imaging (fMRI) studies {3}, including our own {4}, so perhaps what it observed here is a reduction in the learned aversive response (emotional impact) of pain. It would be fascinating to test this possibility in a Pavlovian pain conditioning design.

References

1. Starr CJ, Sawaki L, Wittenberg GF, Burdette JH, Oshiro Y, Quevedo AS, McHaffie JG, Coghill RC. The contribution of the putamen to sensory aspects of pain: insights from structural connectivity and brain lesions. Brain. 2011 Jul; 134(Pt 7): 1987-2002.

 2. Influence of dopaminergically mediated reward on somatosensory decision-making. Pleger B, Ruff CC, Blankenburg F, Klöppel S, Driver J, Dolan RJPLoS Biol 2009 Jul; 7(7):e1000164 PMID: 19636360

3.Direct activation of the ventral striatum in anticipation of aversive stimuli.
Jensen J, McIntosh AR, Crawley AP, Mikulis DJ, Remington G, Kapur SNeuron 2003 Dec 18; 6(40):1251-7 
PMID: 14687557
4.Temporal difference models describe higher-order learning in humans.
Seymour B, O'Doherty JP, Dayan P, Koltzenburg M, Jones AK, Dolan RJ, Friston KJ, Frackowiak RSNature 2004 Jun 10; 6992(429):664-7 
PMID: 15190354
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