Periamygdaloid cortex  Periamygdaloid cortex (or periamygdalar area) is a portion of the rhinencephalon consisting of paleocortex. It is a cortical-like nucleus of the amygdaloid complex. Though considered a nucleus, the periamygdalar area is more commonly associated with cortex due to its layered structure and location on the outer surface of the brain. The periamygdaloid cortex is located on the dorsal surface of the brain bordered by the piriform cortex, entorhinal cortex, perirhinal cortex, periamygdalar claustrum, and anterior amygdaloid area. Its ventromedial and dorsolateral borders are defined by the first myelin bundle of the external capsule, while its remaining borders show no myelinated fiber projections or inputs as well as a higher density of acetylcholinesterase and cholinergic synapses than the neighboring anterior amygdaloid area. The periamygdaloid cortex plays a role in olfaction, and recent studies have shown that it may be involved in many more processes including opiate addiction, assessment of negative emotions, and depression. Additionally, it has been suggested that the left periamygdalar region may play a role in yawning. The periamygdaloid cortex is part of the primary olfactory cortex which receives input from the olfactory bulbs via the lateral olfactory tract. Along with the amygdala, the periamygdaloid cortex conducts cognitive evaluation of the olfactory input it receives and projects it back to the olfactory bulbs. A study of prodynorphin in the periamygdaloid cortex of humans with heroin addiction found that prodynorphin levels were significantly reduced. Further tests were run to determine the link of heroin metabolites to the prodynorphin to rule out ambiguity, but these tests led researchers to confirm that these decreases in prodynorphin were due to chronic heroin use and not a secondary factor. The mRNA-prodynorphin expression of rats undergoing heroin self-administration showed similar results which, paired with tests of affect, indicate that prodynorphin expression in the periamygdaloid cortex of rats correlates with negative affect. With the rat model results in mind, the study's results suggest that human opiate addicts have a lessened ability to manage negative affect due to the effects of heroin on the periamygdaloid cortex.