Notes on placebo
How could the PFC do this?
The two areas of the PreFrontal Cortex most involved in anticipation are the Dorso-Lateral PreFrontal Cortex (DLPFC)
and the OrbitoFrontal Cortex (for flexible incentive learning)
[17,27]. The DLPFC appears to maintain information needed for cognitive control of the body [17], while the OFC is thought to be involved in configuring control mechanisms and in learning based on reward information [27]. The OFC communicates with the DLPFC and the Anterior Cingulate Cortex
to generate and maintain expectation or anticipation. [17].
How could the ACC do this?
The rostral Anterior Cingulate Cortex (rACC)
is also thought to be involved in generating and maintaining expectations, and the Peri-Aqueductal Gray,
and other parts of the brain are involved as well. The rACC shows activation on brain scans relative to "control conditions", and because it's been shown to track changes in reported pain induced by hypnosis [17]. It is also known to have a high concentration of opioid receptors, supporting the finding that the rostral ACC is more reliably activated by endogenous opioids, than is the caudal ACC, which is activated by pain itself. [15]
There is also evidence that the opioid-receptor-containing Peri-Aqueductal Gray of the midbrain shows increased activity during anticipation of relief [17]. The peri-aqueductal gray alters neuronal activity in the rostral ventral medulla, which has 'on' and 'off' cells that are either excited or inhibited by the presence of endogenous or exogenous opioids [14]. Because the orbitofrontal cortex has dense connections with the rACC and with the brainstem, and because the ACC has fiber tracts projecting directly to the peri-aqueductal gray, it is hypothesized that these regions belong to a network that uses cognitive cues to activate an endogenous opioid network [15].
Other areas of cortex and subcortex show increased activity during anticipation of pain relief as well: the primary Sensory cortex, the secondary Sensory cortex, the primary Motor cortex --
RED = primary SENSORY cortex,
BLUE = primary MOTOR cortex
-- and the dorsal amygdala
[17].
RED = primary SENSORY cortex, BLUE = primary MOTOR cortex 
is the major 'way-station' in the pathway for sensing pain, decreased activity in the thalamus during the experience of placebo-induced pain reduction is assumed to come from a blocking or inhibition of pain transmission through the thalamus.