Research interests and activities


My Ph.D. was concerned with the study of healthy human ageing. In particular I used magnetic resonance spectroscopy (MRS) to study non-invasively the concentrations of metabolites in frontal lobe grey matter. The study was published as a paper in 2001. Since that time I have changed track slightly, and whilst still focussing on the brain, I am now involved in the field of pain research:

Pain and laterality/attention

In my previous post (MARIARC & Pain Research Institute, University of Liverpool), I used functional magnetic resonance imaging (FMRI) to look at several aspects of pain processing. In particular, we were interested in looking at the effect of attention and stimulus laterality (i.e. responses that depend on the side of the body stimulated) on the cerebral response to pain. To achieve this we used a simple factorial design, with 2 variables: attention and laterality. Each subject underwent four FMRI scans:

RIGHT HAND
ATTENTION
 RIGHT HAND DISTRACTION
LEFT HAND
DISTRACTION
 :LEFT HAND
 ATTENTION

Where the right hand/left hand indicates which hand was stimulated and attention/distration refers to whether subjects attended to the painful stimulus (thermal pain) applied to the hand or were distracted from it. The distraction task was a global motion discrimination task in which a pattern of (apparently) randomly moving dots were projected to the subject in the scanner. Amongst the jittering dots, the majority were assigned to be noise and their net motion in any direction (during a presentation) was zero. However, for some presentations a noticeable amount of dots were assigned to be "signal" and they had a net movement either to the right or the left. During a distraction scan subjects were asked to continuously assess whether (for each presentation) they could detect a "net motion" of the dots either to the right or the left of the screen, and give a response using button boxes.

The results are summarised in the Figure below (which is taken from the paper reporting these findings):

insula attention/laterality

Where     RA/RV refers to Right hand stimulation without/with Visual distraction, respectively; and
               LA/LV refers to Left hand stimulation without/with Visual distraction, respectively

Laterality effects are represented by blue and red circles. Left hand stimulation gave rise to activation in contralateral (right) posterior insula cortex, whilst right hand stimulation produced the reverse effect (i.e. activation in left posterior insula cortex). These findings occurred irrespective of the attentional "state" of subjects, i.e. irrespective of whether they were being distracted from pain, or were attending to it.

Attention effects were observed in the anterior insula, where if subjects attended to the painful stimulus appled to either the right or the left hand, they activated to a much greater extent than if they were being distracted from the painful stimulus (see yellow circles in above figure).

More detail of the study may be found in the paper, click here to download/open.


Pain and a model of neuropathic pain

More recently I have been involved with development and application of a model of neuropathic pain (developed by Petersen and Rowbotham. "A new human experimental pain model: the heat/capsaicin sensitization model", NeuroReport, 10 (1999) 1511-1516) in healthy subjects studied with FMRI. In particular, we compared the brain response to an intrinsically painful thermal stimulus, to that obtained after treating the stimulation site with capsaicin (the active ingredient in chilli peppers), see Figure below.

Heat/Capsaicin sensitisation procedure

Summary of capsaicin sensitisation protocol. (1) The thenar eminence of the right hand was sensitised with a 5 minute exposure to a warm/hot thermal stimulus (45°C), which is followed by (2) topical application of capsaicin to the treated area. (3) The thenar was covered with a Tegaderm® dressing, and left for 45 minutes (which was found to be a necessary modification to the Petersen & Rowbotham’s original protocol). (4) Following this period the treated area develops a pronounced thermal hyperalgesia, though no increased sensitivity to brush or stretch allodynia, as was reported by Petersen & Rowbotham.

In both conditions we aimed to produce similar pain intensity levels, which meant that we had to adjust the temperature of the thermode to account for the presence of thermal hyperalgesia following application of capsaicin. Hyperalgesia refers to an enhanced pain response to an normally painful stimulus, thus the temperature required to produce the same pain intensity as the pre-capsaicin stimulus is generally significantly reduced. Other studies have refered to this effect as "heat allodynia", where allodynia is defined as pain evoked by a normally innocuous stimulus (e.g. light brushing of the skin with a cotton bud would produce pain in a patient with dynamic mechanical allodyna). I feel that this definition does not adequately describe the enhanced response we see to a lower temperature stimulus post-capsaicin. In practise the difference is small, and probably just reflects personal semantic interpretation, which arise due to difficulty in classifying neuropathic pain conditions.

Preliminary results from this study were published in the IASP Proceedings of the 10th World Congress on Pain and are currently being prepared for submission to an international journal.

Spinal FMRI

More information to follow.