The regions associated with pain modulation are the cingulo-frontal cortex and periaqueductal gray matter.
High densities of opioid receptors are located in all areas of the central nervous system known to be involved in integrating information about pain such as cingulate cortex, periaqueductal gray matter and reticular formation (8) and, these major structures of the medial pain system have a very high concentration of opioid receptors (5).
These structures are connected with the amygdala, hippocampus, hypothalamus, periaqueductal gray matter
, and the limbic regions of the frontal and temporal lobes.
Three areas in the brain stem and diencephalon are specifically implicated in the control of micturition: the dorsolateral pontine tegmentum, the periaqueductal gray matter
, and the preoptic area of the hypothalamus.
The periaqueductal gray matter
(PAG) describes a particular subcortical array of neurons located adjacent to the aqueduct of the fourth ventricle.