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The entorhinal cortex (EC) is a major part of the hippocampal formation of the brain, and is reciprocally connected with the hippocampus. [1]The hippocampal formation, which consists of the hippocampus, perirhinal cortex, the dentate gyrus, the subicular areas and the EC forms one of the most important parts of the limbic system.
View of left entorhinal cortex (red) from beneath the brain, with front of brain at top. Artist's rendering. 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.
The entorhinal cortex (EC) is a structure in the brain located in the medial temporal lobe.The EC is composed of six distinct layers. The superficial (outer) layers, which include layers I through III, are mainly input layers that receive signals from other parts of the EC, but also project to hippocampal structures via the perforant path.
Most external input comes from the adjoining entorhinal cortex, via the axons of the so-called perforant path. These axons arise from layer 2 of the entorhinal cortex (EC), and terminate in the dentate gyrus and CA3. There is also a distinct pathway from layer 3 of the EC directly to CA1, often referred to as the temporoammonic or TA-CA1 pathway.
The presubiculum, parasubiculum, and the entorhinal cortex may also be included. [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]
A recent hypothesis postulates that CA3 sequences are built up pair by pair during memory encoding, relying on precisely timed, phase-precessing input from the entorhinal cortex. [10] This mechanism is based on the synapses of the CA3 recurrent axon corraterals on the dendrites of the CA3 population [11] that form a complete matrix of connections.
The parahippocampal gyrus (or hippocampal gyrus [1]) is a grey matter cortical region of the brain that surrounds the hippocampus and is part of the limbic system. The region plays an important role in memory encoding and retrieval. It has been involved in some cases of hippocampal sclerosis. [2] Asymmetry has been observed in schizophrenia. [3]
The term limbic system was introduced in 1952 by Paul MacLean to describe the set of structures that line the deep edge of the cortex (Latin limbus meaning border): [17] These include the hippocampus, cingulate cortex, olfactory cortex, and amygdala. Paul MacLean later suggested that the limbic structures comprise the neural basis of emotion.