The subiculum (

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

for "support") also known as the subicular complex, or subicular cortex, is the most inferior component of the

hippocampal formation The hippocampal formation is a compound structure in the medial temporal lobe of the brain. It forms a c-shaped bulge on the floor of the inferior horn of the lateral ventricle. Typically, the hippocampal formation is said to included the dent ...

. 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 t ...

and the CA1

hippocampal subfield The hippocampal subfields are four subfields CA1, CA2, CA3, and CA4 that make up the structure of the hippocampus. Regions described in the hippocampus are the head, body, and tail, and other hippocampal subfields include the dentate gyrus, the ...

. The subicular complex comprises a set of four related structures including the 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 the first to use the word "biology" and was a pioneer of neuroanatomy. Life Burdach came from a family of physicians in Leipzig. He graduated in medicine ...

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 hippocampal subfields are four subfields CA1, CA2, CA3, and CA4 that make up the structure of the hippocampus. Regions described in the hippocampus are the head, body, and tail, and other hippocampal subfields include the dentate gyrus, the ...

Structure

The subicular complex 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 cells are the primary excitation units of the mammalian prefrontal cort ...

s and is the main output of the

hippocampus proper The hippocampal subfields are four subfields CA1, CA2, CA3, and CA4 that make up the structure of the hippocampus. Regions described in the hippocampus are the head, body, and tail, and other hippocampal subfields include the dentate gyrus, the ...

. The

pyramidal neurons 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 cells are the primary excitation units of the mammalian prefrontal cort ...

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 hypo ...

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. It is the association cortex in the frontal lobe. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, ...

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 cogni ...

nucleus reuniens The nucleus reuniens is a region of the thalamic midline nuclear group. In the human brain, it is located in the interthalamic adhesion (''massa intermedia''). It is also known as the medioventral nucleus. The nucleus reuniens receives afferen ...

, mammillary nuclei,

and

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 ...

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

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

output:

bursting Bursting, or burst firing, is an extremely diverse general phenomenon of the activation patterns of neurons in the central nervous system where periods of rapid action potential spiking are followed by quiescent periods much longer than typical in ...

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 ento ...

(adjacent to the parahippocampal gyrus),

presubiculum Brodmann area 27 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 postsu ...

, 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, an ...

, 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 corte ...

corresponding to

Brodmann area 27 Brodmann area 27 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 postsu ...

, 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 a ...

, 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 (: hippocampi; via Latin from Ancient Greek, Greek , 'seahorse'), also hippocampus proper, is a major component of the brain of humans and many other vertebrates. In the human brain the hippocampus, the dentate gyrus, and the ...

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 disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

. It has also been implicated in

working memory Working memory is a cognitive system with a limited capacity that can Memory, 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 m ...

and drug

addiction Addiction is a neuropsychological disorder characterized by a persistent and intense urge to use a drug or engage in a behavior that produces natural reward, despite substantial harm and other negative consequences. Repetitive drug use can ...

. 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 neurodegenerative disease and the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As the disease advances, symptoms can include problems wit ...

. Alzheimer's disease pathology is thought to have

prion A prion () is a Proteinopathy, misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), w ...

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