The Myth of the Brain's Pain Matrix?

How does the brain encode physical pain? Which brain areas (if any) respond only to painful stimuli? A new paper reports that one supposedly "pain-selective" brain region, the posterior insula, doesn't actually specifically encode pain - it activates in response to diverse non-painful stimuli as well. The study appears in PLoS Biology and it comes from Giulia Liberati and colleagues of the Université catholique de Louvain, Belgium. Liberati et al. found that the insula responds to non-noxious visual, auditory and tactile stimuli, as well as to painful ones. This was true of every part of the insula they examined, ruling out the possibility of a pain-specific spot within the region. The study included six patients who had electrodes implanted in the insula as part of the programme of treatment for their epilepsy (intracerebral recording). Liberati et al. recorded local field potentials (LFPs) from a total of 72 different sites across all patients, 47 of which were in the insula. Painful stimuli were provided using a small laser. Here's the results from one patient, showing that all categories of stimuli evoked responses.