The subiculum (

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

for "support") is the most inferior component of the

hippocampal formation The hippocampal formation is a compound structure in the Temporal lobe#Medial temporal lobe, medial temporal lobe of the brain. It forms a c-shaped bulge on the floor of the temporal horn of the Lateral ventricles, lateral ventricle. There is no ...

. It lies between the

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 ...

and the CA1 subfield of the

hippocampus proper The hippocampus proper refers to the actual structure of the hippocampus which is made up of three regions or subfields. The subfields CA1, CA2, and CA3 use the initials of cornu Ammonis, an earlier name of the hippocampus. Structure There are ...

. The subicular complex comprises a set of related structures including (as well as subiculum proper) prosubiculum, presubiculum, postsubiculum and parasubiculum.

Name

The subiculum got its name from

Karl Friedrich Burdach Karl Friedrich Burdach (12 June 1776 – 16 July 1847) was a German physiologist. He was born in Leipzig and died in Königsberg. He was the first to use the word "biology" and was a pioneer of neuroanatomy. Life Burdach came from a family of ...

in his three-volume work ''Vom Bau und Leben des Gehirns'' (Vol. 2, §199). He originally named it subiculum cornu ammonis and so associated it with the rest of the

hippocampal subfields The hippocampus proper refers to the actual structure of the hippocampus which is made up of three regions or subfields. The subfields CA1, CA2, and CA3 use the initials of cornu Ammonis, an earlier name of the hippocampus. Structure There are ...

Structure

It receives input from CA1 and entorhinal cortical layer III

pyramidal neuron Pyramidal cells, or pyramidal neurons, are a type of multipolar neuron found in areas of the brain including the cerebral cortex, the hippocampus, and the amygdala. Pyramidal neurons are the primary excitation units of the mammalian prefrontal cor ...

s and is the main output of the hippocampus. The pyramidal neurons send projections to the

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for " nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypot ...

septal nuclei The septal area (medial olfactory area), consisting of the lateral septum and medial septum, is an area in the lower, posterior part of the medial surface of the frontal lobe, and refers to the nearby septum pellucidum. The septal nuclei are loca ...

prefrontal cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46, ...

lateral hypothalamus The lateral hypothalamus (LH), also called the lateral hypothalamic area (LHA), contains the primary orexinergic nucleus within the hypothalamus that widely projects throughout the nervous system; this system of neurons mediates an array of cognit ...

, nucleus reuniens, mammillary nuclei,

and

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 ...

. The pyramidal neurons in the subiculum exhibit transitions between two modes of

action potential An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...

output: bursting and single spiking. The transitions between these two modes is thought to be important for routing information out of the hippocampus. Four component areas have been described:

parasubiculum In the rodent, the parasubiculum is a retrohippocampal isocortical structure, and a major component of the subicular complex. It receives numerous subcortical and cortical inputs, and sends major projections to the superficial layers of the entor ...

(adjacent to the parahippocampal gyrus),

presubiculum Area 27 of Brodmann-1909 is a cytoarchitecturally defined cortical area that is a rostral part of the parahippocampal gyrus. It is commonly regarded as a synonym of presubiculum. The dorsal part of the presubiculum is more commonly known as the ...

, postsubiculum, and prosubiculum.

Parasubiculum

The

contains

grid cells A grid cell is a type of neuron within the entorhinal cortex that fires at regular intervals as an animal navigates an open area, allowing it to understand its position in space by storing and integrating information about location, distance, and ...

, which are neurons responsive to movements in particular directions over particular distances.

Presubiculum

The

is part of the

posterior cortex Posterior cortex usually means the posterior (back) part of the complete cerebral cortex and includes the occipital, parietal, and temporal cortices. In other words, the posterior cortex includes all the cerebral cortex without the frontal cortex ...

corresponding to

Brodmann area 27 Area 27 of Brodmann-1909 is a cytoarchitecturally defined cortical area that is a rostral part of the parahippocampal gyrus. It is commonly regarded as a synonym of presubiculum. The dorsal part of the presubiculum is more commonly known as th ...

, and forms part of the cortical input to the entorhinal-hippocampal spatial/memory system.

Postsubiculum

The dorsal part of the presubiculum is more commonly known as the postsubiculum and is of interest because it contains

head direction cells Head direction (HD) cells are neurons found in a number of brain regions that increase their firing rates above baseline levels only when the animal's head points in a specific direction. They have been reported in rats, monkeys, mice, chinchillas ...

, which are responsive to the facing direction of the head.

Prosubiculum

Prosubiculum is a term often used in reference to monkey anatomy but rarely in rodents, referring to a region located between the CA1 region of the

hippocampus 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, a ...

and the subiculum, and distinguished by higher cell density and smaller cell sizes.

Function

It is believed to play a role in some cases of human

epilepsy Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...

. It has also been implicated in

working memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...

and drug

addiction Addiction is a neuropsychological disorder characterized by a persistent and intense urge to engage in certain behaviors, one of which is the usage of a drug, despite substantial harm and other negative consequences. Repetitive drug use o ...

. It has been suggested that the dorsal subiculum is involved in spatial relations, and the ventral subiculum regulates the hypothalamic-pituitary-adrenal axis.

Clinical significance

Potential role in Alzheimer's disease

Rat studies indicate that lesioning of the subiculum decreases the spread of amyloid-beta in rat models of

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

. Alzheimer's disease pathology is thought to have

prion Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It ...

-like properties. The disease tends to spread in characteristic sequence from the entorhinal cortex through the subiculum.