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

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

, 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 (: cerebra), 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 olfac ...

. 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 (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...

, uncus, and anterior

parahippocampal gyrus The parahippocampal gyrus (or hippocampal gyrus') is a grey matter cortical region, a gyrus 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 ha ...

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

temporal lobe The temporal lobe is one of the four 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 is involved in pr ...

, 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, ...

, 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 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 ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s and

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

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

telencephalon The cerebrum (: cerebra), 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 olf ...

of amphibians, situated

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

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 regions. Recognized as neopallium or

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, ...

, enlarged dorsal areas envelop the paleopallial piriform cortex in

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s and

Old World monkey Old World monkeys are primates in the family Cercopithecidae (). Twenty-four genera and 138 species are recognized, making it the largest primate family. Old World monkey genera include baboons (genus '' Papio''), red colobus (genus '' Piliocolob ...

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

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 file:Common brown robberfly with prey.jpg, A Asilidae, robber fly eating a hoverfly An insectivore is a carnivore, carnivorous animal or plant which eats insects. An alternative term is entomophage, which can also refer to the Entomophagy ...

s than in

primate Primates is an order (biology), order of mammals, which is further divided into the Strepsirrhini, strepsirrhines, which include lemurs, galagos, and Lorisidae, lorisids; and the Haplorhini, haplorhines, which include Tarsiiformes, tarsiers a ...

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