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Current theory states that the areas of the brain involved in pain processing can be divided into 2 networks: the lateral pain system, which projects through lateral thalamic nuclei to brain regions including the primary and secondary somatosensory cortices (SI and SII); and the medial pain system, which projects through medial thalamic nuclei to brain regions including the prefrontal and anterior cingulate cortices. The lateral pain system is thought to be responsible for the sensory aspects of pain such as its location and duration, while the medial pain system is thought to be responsible for the emotional aspects of pain, such as how unpleasant it feels. We are working on a wide range of studies, using a variety of techniques, to investigate the brain areas responsible for processing the different aspects of pain, and how the activity in these brain areas differs in patients with chronic pain conditions.
To enable us to study the medial and lateral pain systems, volunteers are given painful stimuli using a laser and are asked to concentrate on either the location of the pain on their arm (sensory aspect) or the unpleasantness of the pain (emotional aspect). When concentrating on a particular aspect of the pain, brain activity increases in the areas of the brain which process that aspect of the pain. Therefore, by studying brain activity during these two tasks, it is possible to identify brain regions involved in sensory and emotional aspects of pain processing.
Electroencephalography (EEG) studies
Using electroencephalography (EEG) on healthy volunteers, we have investigated the effect that concentrating on the location of pain versus the unpleasantness of pain has on laser evoked potentials (LEPs), which are electrical signals in the brain resulting from painful stimulation with a laser. The results of this study showed that concentrating on the spatial location of pain caused an increase in the amplitude of an early LEP component (N300-T7). This LEP component appears to originate in contralateral SII/insula and possibly SI. Therefore, these results support the idea that the lateral pain system is involved in processing the sensory aspects of pain sensation, particularly localisation. This work was carried out in collaboration with Prof Rolf-Detlef Treede at Johannes Gutenberg University in Germany and Dr Geoff Barrett at the Defence Science and Technology Laboratory (DSTL).
Key publication:
Bentley DE, Watson A, Treede R-D, Barrett G, Youell PD, Kulkarni B, Jones AKP. Differential effects on the laser evoked potential of selectively attending to pain localisation versus pain unpleasantness. Clinical Neurophysiology 2004; 115:1846-1856 |
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| Volunteer undergoing EEG recording using an electrode cap |
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Positron emission tomography (PET) studies
We are also working on similar studies, using positron emission tomography (PET) to image the brains of both healthy volunteers and patients with chronic pain during the performance of these same two tasks. These studies involve comparing the levels of brain activity during attention to the location of the pain with the levels of brain activity during attention to the unpleasantness of the pain, in different regions of the brain. Carrying out these experiments on both healthy volunteers and patients will allow us not only to identify brain regions responsible for processing the sensory and emotional aspects of pain, but also to identify differences in the way pain is processed by patients with chronic pain compared to healthy individuals. This work is a collaboration with Dr Rebecca Elliott at the Neuroscience and Psychiatry Unit, Profs Richard Frackowiak and Karl Friston at the Wellcome Department of Imaging Neuroscience, and Dr Stuart Derbyshire at the University of Pittsburgh Medical Center in the USA.
Key publication:
Kulkarni B, Bentley DE, Elliott R, Youell PD, Watson A, Derbyshire SWG, Frackowiak RSJ, Friston KJ, Jones AKP. Attention to pain localisation and unpleasantness discriminates the functions of the medial and lateral pain systems. Eur J Neurosci 2005; 21: 3133-3142. |
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| Volunteer undergoing PET scan while experiencing painful stimuli from the laser |
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Lateralisation of pain processing
A further study that we have carried out, in collaboration with Drs Irene Tracey and Richard Wise at the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB), involved using functional magnetic resonance imaging (fMRI) to investigate the lateralisation of pain processing in the brain. Healthy volunteers received painful laser stimulation on their right and left calves, and their brain scans were examined to see whether the activity in certain brain regions was the same in both the left and right hemispheres or differed between the hemispheres. In both SI and the thalamus, activation in response to painful stimulation was significantly greater in the hemisphere contralateral (on the opposite side) to the stimulus. This indicates that these areas are involved in processing the sensory aspects of pain, since sensory information is processed in the side of the brain opposite to the side of the body where the sensation is experienced.
Key publication:
Youell PD, Wise RG, Bentley DE, Dickinson MR, King TA, Tracey I, Jones AK. Lateralisation of nociceptive processing in the human brain: a functional magnetic resonance imaging study. Neuroimage 2004; 23(3):1068-1077
Further studies
Other related research being carried out by our group includes:
- investigation of the effect of distraction with noise on the ability to localise pain and on the perceived unpleasantness of the pain;
- examination of how the ability to localise a painful laser stimulus varies with the stimulus intensity;
- a study using transcranial magnetic stimulation (TMS) to assess whether SI is essential to the ability to localise a painful stimulus (in collaboration with Dr Shaheen Hamdy in Gastrointestinal Sciences at Hope Hospital and Prof John Rothwell at the Sobell Department of Motor Neuroscience and Movement Disorders at University College London).
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| Performing TMS over SI |
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