Artificial Consciousness/Neural Correlates/Inter-Organ Connection Models/Entorhinal Cortex Hippocampus Connections
Entorhinal Cortex Hippocampus Connections edit
To understand how the mind can find its place even when the maze is turned and manipulated, we need to understand the idea of size invariant encoding, and the Mapping Grid Neurons found in the Entorhinal Cortex, that connects to CA3. As in the layers of the cerebral cortex, we find a source of signals in a separate layer, in this case the Dentate Gyrus that connects to CA4, a non-pyramidal section of the hippocampus. In this areas we find the familiar mossy Dendrite Neurons that made the first layer of the cerebral cortex. We also find feeding them a layer of granular cells. The Dentate Gyrus connectes to a number of areas within the hippocampal area, suggesting that this system is well informed, but without any understanding yet on how it works. Most of its data seems to come from the Fornix which is thought might connect the hippocampus to the prefrontal cortex.
The Dentate Gyrus, mostly connects with CA3 which is built up of pyramidal Neurons that are highly susceptible to Epileptic Activity. A special connection from the Entorhinal Cortex, is thought to provide grid cell activity creating an underlying mapping grid, that allows CA3 to be used to link signals to locations. Because of the small size of CA3, there is not thought to be enough room for size related data, so most placement signals involve just one or two neurons firing when placement is detected.
Although in some theories CA2 is thought to be directly connected to the Amygdala, and therefore linked to the limbic system, which is tightly linked to the hippocampus, no direct connections to the limbic system approach CA2, which suggest this is a misconstruction. However CA2 is resistant to epileptic activity, and so might act as a buffer between CA3 and CA1.
Via connections called Shaffer Collaterals, signals from CA3 pass throught CA2 To CA1. tightly linking the two areas of the hippocampus. A second set of signals from the Entorhinal cortex, links to CA1, which may or may not mean that it too has some sort of mapping overlay. CA1 in turn connects to both the other half of the Entorhinal Cortex, and to the Subiculum, a body that lies directly between the two hippocampal areas. No one knows yet what the Subiculum does, but it's location and connections to the Nucleus Accumbens make it interesting to the Attention System. Primarily it seems to feed it's output directly to layer 5 of the Entorhinal Cortex. Which might be interesting if the Entorhinal Cortex operates in a manner similar to the Cerebral Cortex. Since this might indicate that it's role is to act as an attention agent, in the Entorhinal Cortex. In much the same way that the thalamus does in the Cerebral Cortex.
The linking of the Hippocampus to signals produced during sleep and memory consolidation, suggest that it has a role in long-term memory. But why such a small part of the brain would have such a large effect, is ellusive. Marr thought that the Hippocampus was a stage in long-term memory, and many researchers have considered that there might be significant compression involved to allow such a small area to control the larger cerebral cortex.