Hippocampus (brain)

This is in contrast to retrograde amnesia, where memories created prior to the event are lost while new memories can still be created.

- Anterograde amnesia

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

- Retrograde 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

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

The unexpected outcome of the surgery was severe anterograde and partial retrograde amnesia; Molaison was unable to form new episodic memories after his surgery and could not remember any events that occurred just before his surgery, but he did retain memories of events that occurred many years earlier extending back into his childhood.

Amnesie

Amnesia

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Deficit in memory caused by brain damage or disease, but it can also be caused temporarily by the use of various sedatives and hypnotic drugs.

Deficit in memory caused by brain damage or disease, but it can also be caused temporarily by the use of various sedatives and hypnotic drugs.

Amnesie

There are two main types of amnesia: retrograde amnesia and anterograde amnesia.

The line processes to make information memory

Memory consolidation

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Category of processes that stabilize a memory trace after its initial acquisition.

Category of processes that stabilize a memory trace after its initial acquisition.

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

Molaison also showed signs of retrograde amnesia spanning a period of about 3 years prior to the surgery suggesting that recently acquired memories of as long as a couple years could remain in the MTL prior to consolidation into other brain areas.

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.

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.

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.

He also had moderate retrograde amnesia, and could not remember most events in the one- to two-year period before surgery, nor some events up to 11 years before, meaning that his amnesia was temporally graded.

Thiamine

Korsakoff syndrome

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Disorder of the central nervous system characterized by amnesia, deficits in explicit memory, and confabulation.

Disorder of the central nervous system characterized by amnesia, deficits in explicit memory, and confabulation.

Thiamine

1) anterograde amnesia, memory loss for events after the onset of the syndrome

2) retrograde amnesia, memory loss extends back for some time before the onset of the syndrome