Hippocampal formation

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Hippocampal formation
CajalHippocampus (modified).png
The hippocampal formation, as drawn by Santiago Ramon y Cajal: DG: dentate gyrus. Sub: subiculum. EC: entorhinal cortex. CA1-CA3: hippocampus proper
Details
Part of Temporal lobe
Identifiers
Latin formatio hippocampi
NeuroNames 177
NeuroLex ID birnlex_7151
FMA 74038
Anatomical terms of neuroanatomy

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 temporal horn of the lateral ventricle. [1] There is no consensus concerning which brain regions are encompassed by the term, with some authors defining it as the dentate gyrus, the hippocampus proper and the subiculum; [2] and others including also the presubiculum, parasubiculum, and entorhinal cortex. [3] The hippocampal formation is thought to play a role in memory, spatial navigation and control of attention. The neural layout and pathways within the hippocampal formation are very similar in all mammals. [4]

Contents

History and function

During the nineteenth and early twentieth centuries, based largely on the observation that, between species, the size of the olfactory bulb varies with the size of the parahippocampal gyrus, the hippocampal formation was thought to be part of the olfactory system. [5]

In 1937, Papez theorized that a circuit including the hippocampal formation constitutes the neural substrate of emotional behavior, [6] and Klüver and Bucy reported that, in monkeys, surgical removal of the hippocampal formation and the amygdaloid complex has a profound effect on emotional responses. [7] [8] As a consequence of these publications, the idea that the hippocampal formation is entirely dedicated to olfaction began to recede. [9]

Medial (inner) surface of the right hemisphere of a human brain Medial surface of cerebral cortex - entorhinal cortex.png
Medial (inner) surface of the right hemisphere of a human brain

In an influential 1947 review, Alf Brodal pointed out that mammal species thought to have no sense of smell nevertheless have fully intact hippocampal formations, that removal of the hippocampal formation did not affect the ability of dogs to perform tasks dependent on olfaction, and that no fibers were actually known that carry information directly from the olfactory bulb to any part of the hippocampal formation. [10] Though massive direct input from the olfactory bulb to the entorhinal cortex has subsequently been found, [11] the current view is that the hippocampal formation is not an integral part of the olfactory system. [12]

In 1900, the Russian neurologist Vladimir Bekhterev described two patients with a significant memory deficit who, on autopsy, were found to have softening of hippocampal and adjacent cortical tissue; [13] and, in 1957, William Beecher Scoville and Brenda Milner reported memory loss in a series of patients subsequent to their removal of the patients' medial temporal lobes. [14] Thanks to these observations and a great deal of subsequent research, it is now broadly accepted that the hippocampal formation plays a role in some aspects of memory. [12]

EEG evidence from 1938 to the present, stimulation evidence from the 1950s, and modern imaging techniques together suggest a role for some part of the hippocampal formation (in concert with the anterior cingulate cortex) in the control of attention. [12]

In 1971, John O'Keefe and his student Jonathan Dostrovsky discovered place cells: neurons in the rat hippocampus whose activity relates to the animal's location within its environment. [15] Despite skepticism from other investigators, O'Keefe and his co-workers, including Lynn Nadel, continued to investigate this question, in a line of work that eventually led to their very influential 1978 book The Hippocampus as a Cognitive Map. [16] The discovery of place cells, together with the discovery of grid cells by May-Britt Moser and Edvard Moser, and the mapping of the function of the hippocampal formation in spatial awareness, led to the joint award of the Nobel Prize in Physiology or Medicine in 2014. In addition to place cells and grid cells, two further classes of spatial cell have since been identified in the hippocampal formation: head direction cells and boundary cells. As with the memory theory, there is now almost universal agreement that the hippocampal formation plays an important role in spatial coding, but the details are widely debated. [17]

Related Research Articles

<span class="mw-page-title-main">Entorhinal cortex</span> Area of the temporal lobe of the brain

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. The EC is the main interface between the hippocampus and neocortex. The EC-hippocampus system plays an important role in declarative (autobiographical/episodic/semantic) memories and in particular spatial memories including memory formation, memory consolidation, and memory optimization in sleep. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane response of classical trace conditioning; the association of impulses from the eye and the ear occurs in the entorhinal cortex.

<span class="mw-page-title-main">Hippocampus</span> Vertebrate brain region involved in memory consolidation

The hippocampus 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, and plays important roles in the consolidation of information from short-term memory to long-term memory, and in spatial memory that enables navigation. The hippocampus is located in the allocortex, with neural projections into the neocortex, in humans as well as other primates. The hippocampus, as the medial pallium, is a structure found in all vertebrates. In humans, it contains two main interlocking parts: the hippocampus proper, and the dentate gyrus.

<span class="mw-page-title-main">Limbic system</span> Set of brain structures involved in emotion and motivation

The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.

<span class="mw-page-title-main">Long-term potentiation</span> Persistent strengthening of synapses based on recent patterns of activity

In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons. The opposite of LTP is long-term depression, which produces a long-lasting decrease in synaptic strength.

<span class="mw-page-title-main">Dentate gyrus</span> Region of the hippocampus in the brain

The dentate gyrus (DG) is part of the hippocampal formation in the temporal lobe of the brain, which also includes the hippocampus and the subiculum. The dentate gyrus is part of the hippocampal trisynaptic circuit and is thought to contribute to the formation of new episodic memories, the spontaneous exploration of novel environments and other functions.

<span class="mw-page-title-main">Olfactory bulb</span> Neural structure

The olfactory bulb 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 (OFC) and the hippocampus where it plays a role in emotion, memory and learning. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb. The main olfactory bulb connects to the amygdala via the piriform cortex of the primary olfactory cortex and directly projects from the main olfactory bulb to specific amygdala areas. The accessory olfactory bulb resides on the dorsal-posterior region of the main olfactory bulb and forms a parallel pathway. Destruction of the olfactory bulb results in ipsilateral anosmia, while irritative lesions of the uncus can result in olfactory and gustatory hallucinations.

<span class="mw-page-title-main">Temporal lobe</span> One of the four lobes of the mammalian brain

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.

<span class="mw-page-title-main">Limbic lobe</span> Region of a cerebral cortex

The limbic lobe is an arc-shaped cortical region of the limbic system, on the medial surface of each cerebral hemisphere of the mammalian brain, consisting of parts of the frontal, parietal and temporal lobes. The term is ambiguous, with some authors including the paraterminal gyrus, the subcallosal area, the cingulate gyrus, the parahippocampal gyrus, the dentate gyrus, the hippocampus and the subiculum; while the Terminologia Anatomica includes the cingulate sulcus, the cingulate gyrus, the isthmus of cingulate gyrus, the fasciolar gyrus, the parahippocampal gyrus, the parahippocampal sulcus, the dentate gyrus, the fimbrodentate sulcus, the fimbria of hippocampus, the collateral sulcus, and the rhinal sulcus, and omits the hippocampus.

<span class="mw-page-title-main">Place cell</span> Place-activated hippocampus cells found in some mammals

A place cell is a kind of pyramidal neuron in the hippocampus that becomes active when an animal enters a particular place in its environment, which is known as the place field. Place cells are thought to act collectively as a cognitive representation of a specific location in space, known as a cognitive map. Place cells work with other types of neurons in the hippocampus and surrounding regions to perform this kind of spatial processing. They have been found in a variety of animals, including rodents, bats, monkeys and humans.

<span class="mw-page-title-main">Papez circuit</span> Neural circuit

The Papez circuit, or medial limbic circuit, is a neural circuit for the control of emotional expression. In 1937, James Papez proposed that the circuit connecting the hypothalamus to the limbic lobe was the basis for emotional experiences. Paul D. MacLean reconceptualized Papez's proposal and coined the term limbic system. MacLean redefined the circuit as the "visceral brain" which consisted of the limbic lobe and its major connections in the forebrain – hypothalamus, amygdala, and septum. Over time, the concept of a forebrain circuit for the control of emotional expression has been modified to include the prefrontal cortex.

<span class="mw-page-title-main">Subiculum</span> Most inferior part of the hippocampal formation

The subiculum is the most inferior component of the hippocampal formation. It lies between the entorhinal cortex and the CA1 subfield of the hippocampus proper.

<span class="mw-page-title-main">Grid cell</span>

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 direction. Grid cells have been found in many animals, including rats, mice, bats, monkeys, and humans.

<span class="mw-page-title-main">Diagonal band of Broca</span>

The diagonal band of Broca interconnects the amygdala and the septal area. It is one of the olfactory structures. It is situated upon the inferior aspect of the brain. It forms the medial margin of the anterior perforated substance.

<span class="mw-page-title-main">Hippocampus anatomy</span>

Hippocampus anatomy describes the physical aspects and properties of the hippocampus, a neural structure in the medial temporal lobe of the brain. It has a distinctive, curved shape that has been likened to the sea-horse monster of Greek mythology and the ram's horns of Amun in Egyptian mythology. This general layout holds across the full range of mammalian species, from hedgehog to human, although the details vary. For example, in the rat, the two hippocampi look similar to a pair of bananas, joined at the stems. In primate brains, including humans, the portion of the hippocampus near the base of the temporal lobe is much broader than the part at the top. Due to the three-dimensional curvature of this structure, two-dimensional sections such as shown are commonly seen. Neuroimaging pictures can show a number of different shapes, depending on the angle and location of the cut.

<span class="mw-page-title-main">Edvard Moser</span> Norwegian psychologist and neuroscientist

Edvard Ingjald Moser is a Norwegian psychologist and neuroscientist, who is a professor at the Norwegian University of Science and Technology (NTNU) in Trondheim. In 2005, he and his then-wife May-Britt Moser discovered grid cells in the brain's medial entorhinal cortex. Grid cells are specialized neurons that provide the brain with a coordinate system and a metric for space. In 2018, he discovered a neural network that expresses a person's sense of time in experiences and memories located in the brain's lateral entorhinal cortex.

<span class="mw-page-title-main">May-Britt Moser</span> Norwegian psychologist and neuroscientist

May-Britt Moser is a Norwegian psychologist and neuroscientist, who is a Professor of Psychology and Neuroscience at the Norwegian University of Science and Technology (NTNU). She and her former husband, Edvard Moser, shared half of the 2014 Nobel Prize in Physiology or Medicine, awarded for work concerning the grid cells in the entorhinal cortex, as well as several additional space-representing cell types in the same circuit that make up the positioning system in the brain. Together with Edvard Moser she established the Moser research environment at NTNU, which they lead. Since 2012 she has headed the Centre for Neural Computation.

<span class="mw-page-title-main">Medial septal nucleus</span>

The medial septal nucleus (MS) is one of the septal nuclei. Neurons in this nucleus give rise to the bulk of efferents from the septal nuclei. A major projection from the medial septal nucleus terminates in the hippocampal formation.

<span class="mw-page-title-main">Granule cell</span> Type of neuron with a very small cell body

The name granule cell has been used for a number of different types of neurons whose only common feature is that they all have very small cell bodies. Granule cells are found within the granular layer of the cerebellum, the dentate gyrus of the hippocampus, the superficial layer of the dorsal cochlear nucleus, the olfactory bulb, and the cerebral cortex.

<span class="mw-page-title-main">John O'Keefe (neuroscientist)</span> American–British neuroscientist

John O'Keefe, is an American-British neuroscientist, psychologist and a professor at the Sainsbury Wellcome Centre for Neural Circuits and Behaviour and the Research Department of Cell and Developmental Biology at University College London. He discovered place cells in the hippocampus, and that they show a specific kind of temporal coding in the form of theta phase precession. He shared the Nobel Prize in Physiology or Medicine in 2014, together with May-Britt Moser and Edvard Moser; he has received several other awards. He has worked at University College London for his entire career, but also held a part-time chair at the Norwegian University of Science and Technology at the behest of his Norwegian collaborators, the Mosers.

<span class="mw-page-title-main">Phase precession</span> Neural mechanism

Phase precession is a neurophysiological process in which the time of firing of action potentials by individual neurons occurs progressively earlier in relation to the phase of the local field potential oscillation with each successive cycle. In place cells, a type of neuron found in the hippocampal region of the brain, phase precession is believed to play a major role in the neural coding of information. John O'Keefe, who later shared the 2014 Nobel Prize in Physiology or Medicine for his discovery that place cells help form a "map" of the body's position in space, co-discovered phase precession with Michael Recce in 1993.

References

  1. ↑ Schultz, Christian; Engelhardt, Maren (2014). "Anatomy of the Hippocampal Formation". The Hippocampus in Clinical Neuroscience. Frontiers of Neurology and Neuroscience. 34: 6–17. doi:10.1159/000360925. ISBN   978-3-318-02567-5. PMID   24777126.
  2. ↑ Martin, JH (2003). "Lymbic system and cerebral circuits for emotions, learning, and memory". Neuroanatomy: text and atlas (third ed.). McGraw-Hill Companies. p. 382. ISBN   0-07-121237-X.
  3. ↑ Amaral, D; Lavenex, P (2007). "Hippocampal neuroanatomy". In Anderson, P; Morris, R; Amaral, D; Bliss, T; I'Keefe (eds.). The hippocampus book (first ed.). New York: Oxford University Press. p. 37. ISBN   9780195100273.
  4. ↑ Anderson, P; Morris, R; Amaral, D; Bliss, T; O'Keefe, J (2007). "The hippocampal formation". In Anderson, P; Morris, R; Amaral, D; Bliss, T; I'Keefe (eds.). The hippocampus book (first ed.). New York: Oxford University Press. p. 3. ISBN   9780195100273.
  5. ↑ Finger, S (2001). "Defining and controlling the circuits of emotion". Origins of neuroscience: a history of explorations into brain function. Oxford/New York: Oxford University Press. p. 286. ISBN   0-19-506503-4.
  6. ↑ Papez, JW (1937). "A proposed mechanism of emotion". Archives of Neurology and Psychiatry. 38 (4): 725–43. doi:10.1001/archneurpsyc.1937.02260220069003.
  7. ↑ Klüver, H; Bucy, PC (1937). ""Psychic blindness" and other symptoms following bilateral temporal lobectomy in Rhesus monkeys". American Journal of Physiology. 119: 352–53.
  8. ↑ Klüver, H; Bucy, PC (1939). "Preliminary analysis of functions of the temporal lobes in monkeys". Archives of Neurology and Psychiatry. 42 (6): 979–1000. doi:10.1001/archneurpsyc.1939.02270240017001.
  9. ↑ Nieuwenhuys, R; Voogd, J; van Huijzen, C (2008). "The greater limbic system". The human central nervous system (fourth ed.). Berlin/Heidelberg/New York: Springer-Verlag. p. 917. ISBN   978-3-540-13441-1.
  10. ↑ Brodal, A (1947). "Hippocampus and the sense of smell". Brain. 70 (Pt 2): 179–222. doi:10.1093/brain/70.2.179. PMID   20261820.
  11. ↑ Shipley, MT; Adamek, GD (1984). "The connections of the mouse olfactory bulb: a study using orthograde and retrograde transport of wheatgerm agglutinin conjugated to horsradish peroxidase". Brain Research Bulletin. 12 (6): 669–688. doi:10.1016/0361-9230(84)90148-5. PMID   6206930. S2CID   4706475.
  12. 1 2 3 Anderson, P; Morris, R; Amaral, D; Bliss, T; O'Keefe, J (2007). "Historical perspective: Proposed functions, biological characteristics, and neurobiological models of the hippocampus". In Anderson, P; Morris, R; Amaral, D; Bliss, T; I'Keefe (eds.). The hippocampus book (first ed.). New York: Oxford University Press. pp. 9–36. ISBN   9780195100273.
  13. ↑ Bekhterev, V (1900). "Demonstration eines gehirns mit zerstörung der vorderen und inneren theile der hirnrinde beider schläfenlappen". Neurologische Zeitenblatte. 19: 990–991.
  14. ↑ Scoville, WB; Milner B (1957). "Loss of Recent Memory After Bilateral Hippocampal Lesions". Journal of Neurology, Neurosurgery, and Psychiatry. 20 (1): 11–21. doi:10.1136/jnnp.20.1.11. PMC   497229 . PMID   13406589.
  15. ↑ O'Keefe J, Dostrovsky J (1971). "The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely-moving rat". Brain Res. 34 (1): 171–75. doi:10.1016/0006-8993(71)90358-1. PMID   5124915.
  16. ↑ O'Keefe, J; Nadel L (1978). The Hippocampus as a Cognitive Map. Oxford University Press. ISBN   0-19-857206-9. Archived from the original on 2011-03-24. Retrieved 2010-01-23.
  17. ↑ Moser, EI; Moser M-B (1998). "Functional differentiation in the hippocampus". Hippocampus. 8 (6): 608–19. doi:10.1002/(SICI)1098-1063(1998)8:6<608::AID-HIPO3>3.0.CO;2-7. PMID   9882018. S2CID   32384692.
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