MadSci Network: Neuroscience

Re: How does the brain store memory and what is its capacity?

Date: Mon Nov 1 23:17:11 1999
Posted By: Xu Lin, Staff, Laboratory of Learning and Memory, Kunming Institute of Zoology
Area of science: Neuroscience
ID: 941443836.Ns

You asked a question that scientists have been looking for the answer to
for a long time. Unfortunately, we are still at the front gate of the 
memory world.

However, a lot of progress has been made which may be useful for you. First of 
all, Ivan Pavlov's theorised that a memory trace is layed down in the brain 
during conditioning as the bases of the memory. A breakthrough was made by T.V.P. 
Bliss in 1973 when he found long-term potentiation (LTP) of excitatory 
postsynaptic potentials in the hippocampus; such phenomena also supported the 
theories proposed by Hebb (1949) who suggested that memory storage is the 
activity-dependent changes of the efficacy of synaptic transmission. Today, there 
are thousands of papers published about LTP. Now, most neurobiologists agree that 
LTP may be the best cellular model for learning and memory. 

There are two parts to the signaling that occurs in the nervous system. The first 
part are called action potentials, which either fire or don't fire, all or none, 
i.e. No or Yes. Therefore, action potentials carry information by their frequency 
of occurance. The second half is synaptic transmission.   The action potentials 
trigger neurotransmitter release which results in excitatory or inhibitory 
postsynaptic potentials which are graded signals. The action potential pretty 
much acts as a binary code, but we can't predict the graded signal of the 
postsynaptic potential. 

There are many research works showing that the areas of memory storage 
are the prefrontal cortex (Goldman-Rakic, Yale Univ.) and the hippocampus 
(Scoville and Milner). O'Keefe (1971) found that there are place cells in the  
hippocampus which associate with a spatial map.  So, based on these developments, 
we believe that synpatic plasticity underlies the storage of information by brain 
areas such as the hippocampus during learning.  

The storage capacity is very difficulty to guess. Some people guess 
that our brain could store 10^13-10^14 bits. Based on the fact that there are 
about 10^10 neurons in our brain and each neuron has several thousands of 
synapses to communicate with other neurons. 

This is a Billions of Dollars question, we all yearn to know the answer.

MADSCI note:  For more about LTP see the following--

how do we learn? 

long term memory

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