“…Anatomical and physiological studies have consistently demonstrated the convergence of these inputs onto spinothalamic tract neurons in the substantia gelatinosa and deeper laminae of the spinal and medullary dorsal horn (Christensen and Perl, 1970;Chung et al, 1979;Light and Perl, 1979a;Gobel et al, 1981;Cruz et al, 1987;Rethelyi et al, 1989;Yoshimura and Jessell, 1989). Most studies have revealed a predominantly excitatory input from both fiber types with the relatively short duration postsynaptic response to stimulation of Aδ fibers preceding the C fiber response (Willis et al, 1974;Menetrey et al, 1977;Chung et al, 1979;Yoshimura and Jessell, 1989); this is consistent with the facilitatory effect of cutaneous thermal stimulation on human nocifensive reflexes (Plaghki et al, 1998).There is evidence, however, that the interactions between the central processes initiated by Aδ and C fiber stimulation are complex, as suggested by the synaptic anatomy of the substantia gelatinosa (Light and Perl, 1979b;Cruz et al, 1987;Rethelyi et al, 1989). Electrophysiological investigations reveal both inhibitory and excitatory postsynaptic responses of nociresponsive dorsal horn neurons, including inhibitory interactions mediated through the activation of Aδ and C fibers (Christensen and Perl, 1970;Chung et al, 1984a;Chung et al, 1984b;Traub and Mendell, 1988;Yoshimura and Jessell, 1989;Tsuruoka et al, 1990;Schneider and Perl, 1994;Shimizu et al, 1995;Sandkuhler et al, 1997;Liu et al, 1998).…”