FYI:There is some important info in this. http://www.macmcm.com/pcp/pcp2000_01.htm "Modulatory factors. Finally, the CNS processing of sensory experience may be simultaneously modulated by two parallel pathways: memory-based modulation and stress- or arousal-induced modulation. The posterior parietal cortex, or sensory association cortex, forms a network with the hippocampus and the amygdala (the brain's memory centers) as well as with the lateral prefrontal cortex. Somatic pain studies have shown that, in response to a stimulus, the recall of a similar past event, along with subsequent interpretation of this memory in the lateral prefrontal cortex, plays a major role in the threat appraisal of a sensory experience. The second modulatory effect is the stress- or arousal-induced response. The pontine locus ceruleus is activated in response to potentially threatening experiences. This region then projects to nearly all other regions of the brain that receive visceral input, causing secretions of norepinephrine and arousal of these sections of the brain. When the secretion of norepinephrine is excessive, these target regions are inhibited. It is of interest that descending projections from the locus coeruleus complex to the sacral spinal cord appear to play a major role in the modulation of distal colonic motor and secretory function."