Hippocampus Flashcards
Where is the hippocampus situated?
Edge of the cortex
The hippocampus is divided into two main regions, what are they?
Cornu Ammonis (CA) divided into four regiions CA1-CA4 Dentate Gyrus (DG) gyrus is the name given to the ridges in the cortex. One of the few areas of the adult brain that exhibits neurogensis
Where does the main input to the hippocampus come from?
Entorhial Coretex (EC)
What is believed to be the primary role of the hippocampus?
Memory and constructing spatial maps.
It does not play a role in procedural memory ( learn new motor skills).
What kind of memory is stored in the hippocampus?
Auto-associative memory. These are patterns representing memories along with some dynamics that complete partial patterns.
What is sparseness?
The average proportion of neurons active at any one time
What is Hebbian plasticity rule
delta wij=eta(xi-a)(xj-a)
where wij is the strength of the connection.
eta is the learning rate
a is the sparseness
In this hippocampus memories need to be learned quickly eta is usually large. Since a is small, there will be a large increase for the connection between two neurons that are active at the same time.
What does too much overlap in patterns prevent?
Retrieval.
When many patterns are stored it is likely that there will be inference between them.
The number of connections is roughly N^2 and the amount of information in a pattern is N so the number of patterns that can be stored is..
N^2/N=N
The capacity is __ if there is sparseness
Larger
Links are __ if in the pattern is active and one inactive, and __ if both are active.
decrease
increased
If both on the increase is eta(1-a)^2
What is the estimated capacity of a network
P=KN/a
Where a is sparseness
k is a constant approx 0.035
and N is the number of neurons
What is the estimated capacity of a network (different way) if there is missing connections
P=NKC/a
where c stands for the fraction of pairs that are connected
If patterns share some fragments or subpatterns then the connections in these sub- patterns become very__
Strong
