User:Paskari/report 5

These are a series of notes, if I get to a point where I find it sufficient, I will parse them into an orderly fashion.
 * Place cells are certain neurons in the hippocampus which are tuned into a region of space (my guess is that they function only in two dimensional space)
 * The problem with understanding the hippocampus is that the input it recieves is not raw data, but heavily processed data arriving from other parts of the visual cortex
 * It is involved in both memory management, and spatial map formation
 * The map does not need to be topographic, only capture the funtional relationship between places
 * Hippocampus uses distributed encoding therefore neighbouring neurons are just as likely to represent distant portions of the environment as close ones.
 * Ensemble coding is used; a group of place cells appear to code one place (Wilson & McNaughton 1983)
 * Can autoassociative memory be incorporated into hippocampal cognitive map formation?
 * According to O'Keefe's cognitive map theory, an environment is represented by a collection of place cells, each of which represents a region of space.
 * The hippocampus encodes allocentric space: the location of an organism with respect to important places in the environment.
 * O'Keefe found that even a small group of neighbouring hippocampal neurons could represent most of the environment
 * All this mumbo jumbo is based on the discovery of place cells. Sort of like how most models are based on Hebbian learning
 * Other parts of the brain involved in spatial map formation involve the posterior parietal lobe and the dorsal striatum.
 * Processing of spatial scenes involves the parahippocampus
 * The right hippocampus is particularly involved in memory for locations within an environment, and the left hippocampus is particularly involved with context-dependent episodic or autobiographical memory
 * The absolute theory of space holds that space is a stationary framework which is seperate from, but can contain, material objects.
 * The relative theory of space holds that space is nothing more than the relations between material objects themeselves.
 * According to O'Keefe, a cognitive map would consist of two major systems: a place system and a misplace system; the former is a memory system which contains information about places in the organisms environment, their spatial relations, and their locations. The former is an update system which signals the presence of new objects, or the absence of old ones. Therefore, the place system is responsible for allowing an animal to move around in a familiar environment, whereas the misplace system enables an animal to explore a new environment.
 * Many senses, such as vision, sound and smell, are used to construct the spatial map
 * Most effort has been expended on object perception as opposed to environment perception

Afferents
There are 4 inputs to the hippocampus
 * 1) inputs from within the same sector
 * 2) inputs from a different sector
 * 3) inputs from the opposite hippocampus
 * 4) inputs from outside the hippocampus

Inputs from within the sector
This input is provided from the pyramidal cells and can be either excitatory or inhibitory.

Inputs from different sectors
?

Inputs from the opposite hippocampus
There is a lot of information being passed back and forth between the left and right hippocampus, but only god, not even O'Keefe, knows why.

Inputs from outside the hippocampus
The hippocampus receives input from the entorhinal cortex which is involved in memory formation, and it forms the main input to the hippocampus. Unfortunately, it also recieves input from a whole host of subcortical inputs, including the amygdala, the medial septum and the diagonal band of Broca, the claustrum, the substantia innominata and the basal nucleus of Meynert, the thalamus, the lateral preoptic and lateral hypothalamic areas, the supramammillary and retromammillary regions, the ventral tegmental area, the tegmental reticular fields, the raphe nuclei, the nucleus reticularis tegementi pontis, the central gray, the dorsal tegmental nucleus, and the locus coeruleus. For a detailed anatomy of all of this input pathways see 'The hippocampus as a Cognitive Map' pages 123-133

Efferents
The main output pathways of the hippocampus are the cingulum, which then projects to the entorhinal cortex bundle which is involved in memory consolidation and displays place cell sensitivity, and the fimbria/fornix. The fornix carries information to the mammillary body and the septal nuclei