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 cortical tissue consists of three cortical laminae (layers of neuronal cell bodies). In comparison, the neocortex ...
. 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
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 the ...
,
perirhinal cortex
The perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. It receives highly processed sensory information from all sensory regions, and is generally accepted to be an important region f ...
, 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 (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
Enzymes () are proteins that a ...
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, it ...
, 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.
Olfactory System
The periamygdaloid cortex is part of the
primary olfactory cortex which receives input from the
olfactory bulb
The olfactory bulb (Latin: ''bulbus olfactorius'') is a grey matter, neural structure of the vertebrate forebrain involved in olfaction, the sense of odor, smell. It sends olfactory information to be further processed in the amygdala, the orbitof ...
s via the
lateral olfactory tract
The olfactory tract 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 cortex, amygdala, and entorhinal cortex. It i ...
. 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 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.
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/
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Cerebral cortex
Olfactory system