Oxford Meeting - November 2002

Opioids and the Brain: fMRI

Richard Rogers Nuffield Department of Anaesthetics and FMRIB- University of Oxford

Analgesia is a complex area to study because it is difficult to quantify the different dimensions of pain. Pain is private, internal and subjective, it cannot be directly observed. Since we have no objective measures of pain, pain intensity is recorded by a variety of self-report scales that attempt to categorize this subjective experience. An objective measure of pain could revolutionise our understanding and management of this complex phenomenon.

Recent developments in functional brain imaging have provided insight into the way the brain processes noxious stimuli. Functional magnetic resonance imaging is a particularly good technique because it is non-invasive and has a comparatively good spatial and temporal resolution.

The Oxford Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB) is an MRC unit set up specifically to exploit this technology using a purpose built 3 Tesla magnet.

Functional magnetic resonance imaging (fMRI) produces both structural and functional information. MRI uses magnetic fields and radio waves to provide an anatomical map of the brain based on the water density of tissues. Changes in local neuronal activity alter the local tissue oxygenation, blood flow and blood volume giving a blood oxygen level dependent (BOLD) signal. Comparison of the BOLD signal under two conditions; a baseline and a stimulus or response e.g. noxious stimulus, provides a measure of function. 

Functional Brain Imaging has revealed a network of central sites that respond to noxious stimuli. This pain matrix includes the thalamus and insular, lingulate and sensory cortices.

The pain group at FMRIB in Oxford has looked at how analgesics and psychological manipulation alters the activity of the pain matrix. In this talk, I present some of the units work on measuring the analgesia produced by remifentanil. This work suggests that the reduction in behavioural pain score seen with remifentanil can be imaged and that this reduction in pain can be objectively quantified.

Functional MRI has the potential to measure analgesia objectively and provide information on subcomponents of pain.