Thalamic nociceptive systems.

A role for thalamic structures in the processing of signals of nociception and pain has been suggested on the basis of clinical data since the turn of the century. Searches for a 'pain centre' by lesion or stimulation were often disappointing and the electrophysiological data were rare and usually contradictory. However, recent electrophysiological anatomical and neuropharmacological studies, made in various species (mainly rat and monkey) appear now progressively to give some clues in the understanding of pain process at the thalamic level. These studies have been mainly concerned with the areas receiving projections from ascending spinal pathways conveying noxious inputs, either directly by the spinothalamic tract or indirectly by the spinoreticulothalamic pathway. The eventual respective roles of these thalamic structures are considered. Electrophysiological recordings from thalamic structures in a model of experimental pain, arthritic rats, are also presented.