|MadSci Network: Neuroscience|
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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