Hippocampal formation
Encyclopedia
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Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. There is currently no consensus concerning which brain regions are encompassed by the term, with some authors defining it as the dentate gyrus
Dentate gyrus
The dentate gyrus is part of the hippocampal formation. It is thought to contribute to new memories as well as other functional roles. It is notable as being one of a select few brain structures currently known to have high rates of neurogenesis in adult rats, .The dentate gyrus cells receive...
, the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
proper and the subiculum
Subiculum
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.-Paths:...
; and others including also the presubiculum, parasubiculum
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 entorhinal cortex .The parasubicular area is a...
, and entorhinal cortex
Entorhinal cortex
The entorhinal cortex is located in the medial temporal lobe and functions as a hub in a widespread network for memory and navigation. The EC is the main interface between the hippocampus and neocortex...
. 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.
Function
During the nineteenth and early twentieth centuries, based largely on the observation that, between species, the size of the olfactory bulbOlfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
varies with the size of the parahippocampal gyrus, the hippocampal formation was thought to be part of the olfactory system.
In 1937 Papez
James Papez
James Papez was an American neuroanatomist. Papez received his MD from the University of Minnesota College of Medicine and Surgery. He is most famous for his 1937 description of the Papez circuit which is a neural pathway in the brain thought to be involved in the cortical control of emotion...
theorized that a circuit including the hippocampal formation constitutes the neural substrate of emotional behavior, and Klüver
Heinrich Klüver
Heinrich Klüver was a German-American psychologist born in Holstein, Germany.After having served in the Imperial Germany Army during World War I, he studied at both the University of Hamburg and the University of Berlin from 1920-23. In the latter year, he arrived in the United States to attend...
and Bucy
Paul Bucy
Paul Bucy was an American neuropathologist who was a native of Hubbard, Iowa. He studied medicine at the University of Iowa, and afterwards was an assistant to neurosurgeon Percival Bailey at the University of Chicago...
reported that, in monkeys, resection
Segmental resection
Segmental resection is a surgical procedure to remove part of an organ or gland. It may also be used to remove a tumor and normal tissue around it. In lung cancer surgery, segmental resection refers to removing a section of a lobe of the lung.- External links :* entry in the public domain NCI...
involving the hippocampal formation and the amygdaloid complex
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
has a profound effect on emotional responses. As a consequence of these publications, the idea that the hippocampal formation is entirely dedicated to olfaction
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
began to recede. (Today there is little support for the idea that the hippocampal formation is directly involved in emotion.)
In an influential 1947 review, Alf Brodal
Alf Brodal
Alf Brodal was a Norwegian professor of anatomy.-Career:He was born in Kristiania as a son of the doctor of engineering Peter Brodal and his wife Helene Kathrine Obenauer . He took the examen artium in 1929 and the cand.med. degree in 1937. He took the dr.med...
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
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
were actually known that carry information directly from the olfactory bulb to any part of the hippocampal formation. Though massive direct input from the olfactory bulb to the entorhinal cortex has subsequently been found, the current view is that the hippocampal formation is not an integral part of the olfactory system.
In 1900, the Russian neurologist Vladimir Bekhterev
Vladimir Bekhterev
Vladimir Mikhailovich Bekhterev was a Russian Neurologist and the Father of Objective Psychology. He is best known for noting the role of the hippocampus in memory, his study of reflexes, and Bekhterev’s Disease...
described two patients with a significant memory deficit who, on autopsy, were found to have softening of hippocampal and adjacent cortical tissue; and, in 1957, Scoville and Milner reported memory loss in a series of patients subsequent to their removal of the patients' medial temporal lobes. 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.
EEG
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
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.
In 1971, John O'Keefe and his student Jonathan Dostrovsky discovered neurons in the rat hippocampus that appeared to show activity related to the rat's location within its environment. Despite skepticism
Skepticism
Skepticism has many definitions, but generally refers to any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere...
from other investigators, O'Keefe and his co-workers, including Lynn Nadel
Lynn Nadel
Lynn Nadel is the Regents' Professor of Psychology at the University of Arizona. Nadel specializes in memory, and has investigated the role of the hippocampus in memory formation. Together with John O'Keefe, he coauthored the influential 1978 book The Hippocampus as a Cognitive Map, which...
, 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. 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.