Periamygdaloid cortex (or periamygdalar area) is a portion of the

rhinencephalon In animal anatomy, the rhinencephalon (from the Greek, ῥίς, ''rhis'' = "nose", and ἐγκέφαλος, ''enkephalos'' = "brain"), also called the smell-brain or olfactory brain, is a part of the brain involved with smell (i.e. olfaction). ...

consisting of

paleocortex In anatomy of animals, the paleocortex, or paleopallium, is a region within the telencephalon in the vertebrate brain. This type of cerebral cortex, cortical tissue consists of three cortical laminae (layers of perikaryon, neuronal cell bodies). I ...

. 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 The piriform cortex, or pyriform cortex, is a region in the brain, part of the rhinencephalon situated in the cerebrum. The function of the piriform cortex relates to the sense of smell. Structure The piriform cortex is part of the rhinencephal ...

entorhinal cortex The entorhinal cortex (EC) is an area of the brain's allocortex, located in the medial temporal lobe, whose functions include being a widespread network hub for memory, navigation, and the perception of time.Integrating time from experience in t ...

perirhinal cortex The perirhinal cortex is a brain cortex, cortical region in the medial temporal lobe that is made up of Brodmann areas Brodmann area 35, 35 and Brodmann area 36, 36. It receives highly processed sensory information from all sensory regions, and i ...

, periamygdalar claustrum, and anterior amygdaloid area. Its ventromedial and dorsolateral borders are defined by the first myelin bundle of the

external capsule The external capsule is a series of white matter fiber tracts in the brain. These fibers run between the most lateral (toward the side of the head) segment of the lentiform nucleus (more specifically the putamen) and the claustrum. The white matt ...

, while its remaining borders show no myelinated fiber projections or inputs as well as a higher density of

acetylcholinesterase Acetylcholinesterase (HUGO Gene Nomenclature Committee, HGNC symbol ACHE; EC 3.1.1.7; systematic name acetylcholine acetylhydrolase), also known as AChE, AChase or acetylhydrolase, is the primary cholinesterase in the body. It is an enzyme th ...

and cholinergic synapses than the neighboring anterior amygdaloid area. The periamygdaloid cortex plays a role in

olfaction The sense of smell, or olfaction, is the special sense through which smells (or odors) are perceived. The sense of smell has many functions, including detecting desirable foods, hazards, and pheromones, and plays a role in taste. In humans, ...

, and recent studies have shown that it may be involved in many more processes including

opiate addiction Opioid use disorder (OUD) is a substance use disorder characterized by cravings for opioids, continued use despite physical and/or psychological deterioration, increased tolerance with use, and withdrawal symptoms after discontinuing opioids. ...

, assessment of negative emotions, and depression. Additionally, it has been suggested that the left periamygdalar region may play a role in

yawn A yawn is a reflex in vertebrate animals characterized by a long inspiratory phase with gradual mouth gaping, followed by a brief climax (or acme) with muscle stretching, and a rapid expiratory phase with muscle relaxation, which typically last ...

ing.

Olfactory System

The periamygdaloid cortex is part of the

primary olfactory cortex The primary olfactory cortex (POC) is a portion of the cerebral cortex. It is found in the inferior part of the temporal lobe of the brain. It receives input from the olfactory tract. It is involved in the sense of smell (olfaction). Structure ...

which receives input from the

olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...

s via the

lateral olfactory tract The olfactory tract (olfactory peduncle or olfactory stalk) is a bilateral bundle of afferent nerve fibers from the mitral and tufted cells of the olfactory bulb that connects to several target regions in the brain, including the piriform cort ...

. Along with the amygdala, the periamygdaloid cortex conducts cognitive evaluation of the olfactory input it receives and projects it back to the olfactory bulbs.

Addiction and Depression

A study of

prodynorphin Prodynorphin, also known as proenkephalin B, is an opioid polypeptide hormone involved with chemical signal transduction and cell communication. The gene for prodynorphin is expressed in the endometrium and the striatum, and its gene map locus is 2 ...

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 In psychology, negative affectivity (NA), or negative affect, is a personality variable that involves the experience of negative emotions and poor self-concept. Negative affectivity subsumes a variety of negative emotions, including anger, contem ...

. 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. Similar to its proposed mechanism of action in heroin addiction, prodynorphin in the periamygdaloid cortex has been shown to be significantly decreased in Major Depressive Disorder sufferers. This further implicates prodynorphin in the control of negative affect in humans and thus suggests that the periamygdaloid cortex is partially responsible for affect in humans.

Negative Emotion Assessment

The activity of various brain regions were assessed during exposure-recognition tasks of static and dynamic facial expressions of anger and happiness. Both the left and right periamygdaloid cortex voxels studied showed differential activation when the subject was tasked with recognizing dynamic expressions of anger compared to neutral, control expressions. This was not observed in static expressions of anger or in any expressions of happiness. These results suggest that the periamygdaloid cortex may be partially responsible for interpreting facial expressions and body language that indicate anger. This demonstrated involvement of the periamygdaloid cortex in dynamic anger assessment adds to the discoveries in more recent research linking the periamygdaloid cortex with prodynorphin expression.

References

External links

* http://braininfo.rprc.washington.edu/centraldirectory.aspx?ID=166 * https://web.archive.org/web/20091208125451/http://isc.temple.edu/neuroanatomy/lab/atlas/bgfgic/ {{Authority control Cerebral cortex Olfactory system