Hippocampus (brain)
The line processes to make information memory
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Systematic studies of anterograde amnesia started to emerge in the 1960s and 1970s.

- Memory consolidation

This suggests that memory consolidation for different types of memory takes place in different regions of the brain.

- Anterograde amnesia
Hippocampus (brain)

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Overall

Humans have two hippocampi, one in each hemisphere of the brain. They are located in the medial temporal lobes of the cerebrum. In this lateral view of the human brain, the frontal lobe is at the left, the occipital lobe at the right, and the temporal and parietal lobes have largely been removed to reveal one of the hippocampi underneath.

Hippocampus

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Major component of the brain of humans and other vertebrates.

Major component of the brain of humans and other vertebrates.

Humans have two hippocampi, one in each hemisphere of the brain. They are located in the medial temporal lobes of the cerebrum. In this lateral view of the human brain, the frontal lobe is at the left, the occipital lobe at the right, and the temporal and parietal lobes have largely been removed to reveal one of the hippocampi underneath.
Image 1: The human hippocampus and fornix (left) compared with a seahorse (right)
Image 2: Cross-section of cerebral hemisphere showing structure and location of hippocampus
Image 3: Coronal section of the brain of a macaque monkey, showing hippocampus (circled)
Image 4: Basic circuit of the hippocampus, as drawn by Cajal DG: dentate gyrus. Sub: subiculum. EC: entorhinal cortex
Image 5: Hippocampal location and regions
Rats and cognitive maps
Image 6: Spatial firing patterns of 8 place cells recorded from the CA1 layer of a rat. The rat ran back and forth along an elevated track, stopping at each end to eat a small food reward. Dots indicate positions where action potentials were recorded, with color indicating which neuron emitted that action potential.
Image 7: Examples of rat hippocampal EEG and CA1 neural activity in the theta (awake/behaving) and LIA (slow-wave sleep) modes. Each plot shows 20 seconds of data, with a hippocampal EEG trace at the top, spike rasters from 40 simultaneously recorded CA1 pyramidal cells in the middle (each raster line represents a different cell), and a plot of running speed at the bottom. The top plot represents a time period during which the rat was actively searching for scattered food pellets. For the bottom plot the rat was asleep.
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Image 9: An EEG showing epilepsy right-hippocampal seizure onset
Image 10: An EEG showing epilepsy left-hippocampal seizure onset
Image 11: Drawing by Italian pathologist Camillo Golgi of a hippocampus stained using the silver nitrate method
thumb|Hippocampus highlighted in green on coronal T1 MRI images
thumb|Hippocampus highlighted in green on sagittal T1 MRI images
thumb|Hippocampus highlighted in green on transversal T1 MRI images

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.

People with extensive, bilateral hippocampal damage may experience anterograde amnesia: the inability to form and retain new memories.

Long-term memory

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Stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely.

Stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely.

Synaptic Consolidation is the process by which items are transferred from short-term to long-term memory.

His subsequent total anterograde amnesia and partial retrograde amnesia provided the first evidence for the localization of memory function, and further clarified the differences between declarative and procedural memory.

Hippocampus as seen in red

Explicit memory

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One of the two main types of long-term human memory, the other of which is implicit memory.

One of the two main types of long-term human memory, the other of which is implicit memory.

Hippocampus as seen in red
Amygdala as seen in red
The Morris water maze

Specifically, sleep's unique properties enhance memory consolidation, such as the reactivation of newly learned memories during sleep.

Guy Pearce plays an ex-insurance investigator suffering from severe anterograde amnesia caused by a head injury.

Retrograde amnesia

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Loss of memory-access to events that occurred or information that was learned in the past.

Loss of memory-access to events that occurred or information that was learned in the past.

Anterograde amnesia is a similar condition that deals with the inability to form new memories following the onset of an injury or disease.

The hippocampus deals largely with memory consolidation, where information from the working memory and short-term memory is encoded into long-term storage for future retrieval. Amnesic patients with damage to the hippocampus are able to demonstrate some degree of unimpaired semantic memory, despite a loss of episodic memory, due to spared parahippocampal cortex. In other words, retrograde amnesics "know" about information or skill, but cannot "remember" how they do.

Molaison in 1953 before his surgery

Henry Molaison

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American who had a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy.

American who had a bilateral medial temporal lobectomy to surgically resect the anterior two thirds of his hippocampi, parahippocampal cortices, entorhinal cortices, piriform cortices, and amygdalae in an attempt to cure his epilepsy.

Molaison in 1953 before his surgery
Most of Molaison's two hippocampi were removed bilaterally.

After the surgery, which was partially successful in controlling his seizures, Molaison developed severe anterograde amnesia: although his working memory and procedural memory were intact, he could not commit new events to his explicit memory.

Another contribution of Molaison to understanding of human memory regards the neural structures of the memory consolidation process, which is responsible for forming stable long-term memories (Eysenck & Keane, 2005).

Episodic memory

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Memory of everyday events that can be explicitly stated or conjured.

Memory of everyday events that can be explicitly stated or conjured.

Others believe the hippocampus only stores episodic memories for a short time, after which the memories are consolidated to the neocortex.

For example, anterograde amnesia, from damage of the medial temporal lobe, is an impairment of declarative memory that affects both episodic and semantic memory operations.