Stimulation some point of auricle activating the descending pain inhibition pathways from brain stem, thus inhibiting the ascending pain pathways.
The application of auricular acupuncture gives pain killing effect by activating the descending pain inhibition pathways  along the dorsal side of spinal cord where the dorsal horn cells are located.
Therefore,deep brain stimulation can produce analgesic effect by compressing the dorsolateral funiculus in the spinal canal.
Nociceptive pain can trigger activity in the hypothalamus,peri aquaductal grey matter,somatosensory cortex and pre frontal cortex, but deep brain stimulation can also activate the same areas in the subcortical thalamus to produce analgesic effect by increasing the concentration of beta endorphins and can be blocked by administation of some auricle point "lung-shenmen"
In that point as reflexes on the surface of ear running along the neuron fibers from earlobe to the brain,from the brain through the spinal cord,then the body'S correspondence area.
The outer ear running the pheripheral brances of vagal nerve,great auricular nerve,auriculo temporal nerve as branch of trigeminal nerve and lesser occipital nerve.
These point is neurovascular points and connected CNS lkmbic system and releasing CRH and  POMC to release ACTH and beta endorphins.

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Evidence based Complement Altern Med 2015

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Evidence based Complement Altern Med 2013