A model neuronal network explaining placebo analgesia-related activation of ACC neurons. Placebo leads to activation of inhibitory neurons within the ACC. These inhibitory neurons then release an inhibitory neurotransmitter, GABA. GABA acts on postsynaptic GABA receptors to inhibit ACC neurons that are involved in pain perception. In some neurons, endogenous neuropeptides such as enkaphalin (Enk) may also be released to produce similar inhibitory effects (a). Inhibitory neurons may also affect ACC neurons that form descending facilitatory innervations with the spinal cord dorsal horn. Activation of inhibitory neurons within the ACC causes the reduction of descending facilitatory influences. The reduced facilitatory influence on spinal nociceptive transmission therefore produces analgesic effects.