Entorhinal cortex
Encyclopedia
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 EC-hippocampus system
plays an important role in autobiographical/declarative/episodic 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.
. In primates it is located at the rostral end of the temporal lobe and stretches dorsolaterally. It is usually divided into medial
and lateral regions with three bands with distinct properties and connectivity running perpendicular across the whole area. A distinguishing characteristic of the EC is the lack of cell bodies where layer IV should be; this layer is called the lamina dissecans.
The superficial layers - layers II and III - of EC project to the dentate gyrus
and hippocampus
: Layer II projects primarily to dentate gyrus
and hippocampal region CA3; layer III projects primarily to hippocampal region CA1 and the subiculum
. These layers receive input from other cortical areas, especially associational, perirhinal
, and parahippocampal
cortices, as well as prefrontal cortex
. EC as a whole, therefore, receives highly-processed input from every sensory modality, as well as input relating to ongoing cognitive processes, though it should be stressed that, within EC, this information remains at least partially segregated.
The deep layers, especially layer V, receive one of the three main outputs of the hippocampus
and, in turn, reciprocate connections from other cortical areas that project to superficial EC.
The rodent entorhinal cortex shows a modular organization, with different properties and connections in different areas.
Neurons in the lateral entorhinal cortex exhibit little spatial selectivity, whereas neurons of the medial entorhinal cortex (MEA), exhibit multiple "place fields" that are arranged in an hexagonal pattern, and are therefore called "grid cells
". These fields and spacing between fields increase from the dorso-lateral MEA to the ventro-medial MEA.
Single-unit recording
of neurons in humans playing video games find path cells in the EC, the activity of which indicates whether a person is taking a clockwise or counterclockwise path. Such EC "direction" path cells show this directional activity irrespective of the location of where a person experiences themselves which contrasts them to place cells in the hippocampus which are activated by specific locations.
EC neurons process general information such as directional activity in the environment which contrasts to that of the hippocampal neurons, which usually encode information about specific places. This suggests that EC encodes general properties about current contexts that are then used by hippocampus to create unique representations from combinations of these properties.
.
For delineating the Entorhinal cortex, see Desikan RS, Ségonne F, Fischl B, Quinn BT, Dickerson BC, Blacker D, Buckner RL, Dale AM, Maguire RP, Hyman BT, Albert MS, Killiany RJ. An automated labeling system for subdividing the human cerebral cortex on MRI scans into gyral based regions of interest. Neuroimage. 2006 Jul 1;31(3):968-80.
Memory
In psychology, memory is an organism's ability to store, retain, and recall information and experiences. Traditional studies of memory began in the fields of philosophy, including techniques of artificially enhancing memory....
and navigation. The EC is the main interface between 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...
and neocortex
Neocortex
The neocortex , also called the neopallium and isocortex , is a part of the brain of mammals. It is the outer layer of the cerebral hemispheres, and made up of six layers, labelled I to VI...
. The EC-hippocampus system
EC-hippocampus system
The Entorhinal Cortex is a major part of the hippocampal formation of the human brain, and is reciprocally connected with the hippocampus....
plays an important role in autobiographical/declarative/episodic memories and in particular spatial memories
Spatial memory
In cognitive psychology and neuroscience, spatial memory is the part of memory responsible for recording information about one's environment and its spatial orientation. For example, a person's spatial memory is required in order to navigate around a familiar city, just as a rat's spatial memory is...
including memory formation, memory consolidation
Memory consolidation
Memory consolidation is a category of processes that stabilize a memory trace after the initial acquisition. Consolidation is distinguished into two specific processes, synaptic consolidation, which occurs within the first few hours after learning, and system consolidation, where...
, and memory optimization in sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...
. The EC is also responsible for the pre-processing (familiarity) of the input signals in the reflex nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
response of classical trace conditioning, the association of impulses from the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
and the ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
occurs in the entorhinal cortex.
Anatomy
In rodents, the EC is located at the caudal end of the temporal lobeTemporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
. In primates it is located at the rostral end of the temporal lobe and stretches dorsolaterally. It is usually divided into medial
Medial
- Medial magmas :In abstract algebra, a medial magma is a set with a binary operation which satisfies the identity \cdot = \cdot , or more simply, xy\cdot uv = xu\cdot yv...
and lateral regions with three bands with distinct properties and connectivity running perpendicular across the whole area. A distinguishing characteristic of the EC is the lack of cell bodies where layer IV should be; this layer is called the lamina dissecans.
Inputs and outputs
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...
and 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...
: Layer II projects primarily to 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...
and hippocampal region CA3; layer III projects primarily to hippocampal region CA1 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:...
. These layers receive input from other cortical areas, especially associational, perirhinal
Perirhinal cortex
Perirhinal cortex is a cortical region in the medial temporal lobe that is made up of Brodmann areas 35 and 36. In rats, it is located along and dorsal to the rhinal sulcus. It receives highly-processed sensory information from all sensory regions, and is generally accepted to be an important...
, and parahippocampal
Parahippocampal gyrus
The parahippocampal gyrus is a grey matter cortical region of the brain that surrounds the hippocampus. This region plays an important role in memory encoding and retrieval....
cortices, as well as prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
. EC as a whole, therefore, receives highly-processed input from every sensory modality, as well as input relating to ongoing cognitive processes, though it should be stressed that, within EC, this information remains at least partially segregated.
The deep layers, especially layer V, receive one of the three main outputs of 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...
and, in turn, reciprocate connections from other cortical areas that project to superficial EC.
The rodent entorhinal cortex shows a modular organization, with different properties and connections in different areas.
Neuron information processing
In 2005, it was discovered that entorhinal cortex contains a neural map of the spatial environment in rats.Neurons in the lateral entorhinal cortex exhibit little spatial selectivity, whereas neurons of the medial entorhinal cortex (MEA), exhibit multiple "place fields" that are arranged in an hexagonal pattern, and are therefore called "grid cells
Grid cells
A grid cell is a type of neuron that has been found in the brains of rats and mice; and it is likely to exist in other animals including humans...
". These fields and spacing between fields increase from the dorso-lateral MEA to the ventro-medial MEA.
Single-unit recording
Single-unit recording
In neurophysiology and neurology, single-unit recording is the use of an electrode to record the electrophysiological activity from a single neuron.-History:...
of neurons in humans playing video games find path cells in the EC, the activity of which indicates whether a person is taking a clockwise or counterclockwise path. Such EC "direction" path cells show this directional activity irrespective of the location of where a person experiences themselves which contrasts them to place cells in the hippocampus which are activated by specific locations.
EC neurons process general information such as directional activity in the environment which contrasts to that of the hippocampal neurons, which usually encode information about specific places. This suggests that EC encodes general properties about current contexts that are then used by hippocampus to create unique representations from combinations of these properties.
Alzheimer's Disease
The entorhinal cortex is one of the first areas to be affected in Alzheimer's DiseaseAlzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
.
Brodmann's areas
- Brodmann area 28Brodmann area 28-Guenon:Brodmann area 28 is a subdivision of the cerebral cortex of the guenon defined on the basis of cytoarchitecture. Brodmann regarded its location adjacent to the hippocampus as imprecisely represented in the illustration of the cortex of the guenon brain in Brodmann-1909...
is known as the "area entorhinalis" - Brodmann area 34Brodmann area 34Brodmann area 34 is a part of the brain.It has been described as part of the entorhinal area.It has been described as part of the superior temporal gyrus....
is known as the "area entorhinalis dorsalis"
External links
- NIF Search - Entorhinal Cortex via the Neuroscience Information FrameworkNeuroscience Information FrameworkThe Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...
For delineating the Entorhinal cortex, see Desikan RS, Ségonne F, Fischl B, Quinn BT, Dickerson BC, Blacker D, Buckner RL, Dale AM, Maguire RP, Hyman BT, Albert MS, Killiany RJ. An automated labeling system for subdividing the human cerebral cortex on MRI scans into gyral based regions of interest. Neuroimage. 2006 Jul 1;31(3):968-80.