Recent pain research has concentrated heavily on excitatory processes. However, noxious stimuli activate excitatory and inhibitory systems. As failure of inhibition could underlie some forms of pathological pain, it may be argued that a full understanding of the mechanisms underlying the development of pain states can only come from a consideration of all the central sequelae of injurious stimuli. [berkley; blumberg et al.; coderre & katz; dickenson; mcmahon; weisenfeld-hallin et al.]