The piriform cortex, or pyriform cortex, is a region in the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

, part 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). ...

situated in the

cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...

. The function of the piriform cortex relates to the sense of smell.

Structure

The piriform cortex is part of the

situated in the

. In human anatomy, the piriform cortex has been described as consisting of the cortical

amygdala The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...

uncus The uncus is an anterior extremity of the parahippocampal gyrus. It is separated from the apex of the temporal lobe by a slight fissure called the incisura temporalis (also called rhinal sulcus). Although superficially continuous with the hippo ...

, and anterior

parahippocampal gyrus The parahippocampal gyrus (or hippocampal gyrus') is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. The region plays an important role in memory encoding and retrieval. It has been inv ...

. More specifically, the human piriform cortex is located between the insula and the

temporal lobe The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain. The temporal lobe ...

, anteriorly and laterally of the amygdala.Howard, J. D., Plailly, J., Grueschow, M., Haynes, J. D., & Gottfried, J. A. (2009). Odor quality coding and categorization in human posterior piriform cortex. Nature neuroscience, 12(7), 932-938. Supplementary material, p.4

Function

The function of the piriform cortex relates to

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 ...

, which is the perception of smell. This has been particularly shown in humans for the posterior piriform cortex. The piriform cortex in rodents and some primates has been shown to harbor cells expressing markers of plasticity such as

doublecortin Neuronal migration protein doublecortin, also known as doublin or lissencephalin-X is a protein that in humans is encoded by the DCX gene. Function Doublecortin (DCX) is a microtubule-associated protein expressed by neuronal precursor cells an ...

and PSA-NCAM which are modulated by the noradrenergic neurotransmitter system.

Clinical significance

The piriform cortex contains a critical, functionally defined epileptogenic trigger zone, "Area Tempestas". From this site in piriform cortex chemical and electrically evoked seizures can be triggered. It is the site of action for the proconvulsant action of chemoconvulsants.

Other animals

Sometimes called the ''olfactory cortex'', ''olfactory lobe'' or ''paleopallium'', piriform cortical regions are present in the brains of

amphibians Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbore ...

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

s and

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s. The piriform cortex is among three areas that emerge in the

telencephalon The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...

of amphibians, situated

caudally Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

to a dorsal area, which is caudal to a hippocampal area. Further along the phylogenic timeline, the telencephalic bulb of reptiles as viewed in a cross section of the transverse plane extends with the archipallial hippocampus folding toward the midline and down as the dorsal area begins to form a recognizable cortex. As mammalian brains developed, volume of the dorsal cortex increased in slightly greater proportion, as compared proportionally with increased overall brain volume, until it enveloped the

hippocampal The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, an ...

regions. Recognized as

neopallium The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, s ...

neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...

, enlarged dorsal areas envelop the paleopallial piriform cortex in

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s and

Old World monkey Old World monkey is the common English name for a family of primates known taxonomically as the Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons ...

s. Among taxonomic groupings of mammals, the piriform cortex and 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 ...

become proportionally smaller in the brains of phylogenically younger species. The piriform cortex occupies a greater proportion of the overall brain and of the telencephalic brains of

insectivore A robber fly eating a hoverfly An insectivore is a carnivorous animal or plant that eats insects. An alternative term is entomophage, which can also refer to the human practice of eating insects. The first vertebrate insectivores wer ...

s than in

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including huma ...

s. The piriform cortex continues to occupy a consistent albeit small and declining proportion of the increasingly large

in the most recent primate species while the volume of the olfactory bulb becomes less in proportion.

References

External links