WULFRAM GERSTNER AND L. F. ABBOTT (1996)
Learning Navigational Maps Through Potentiation and Modulation of Hippocampal Place Cells
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Keywords: hippocampal place cell, long term potentiation/depression (LTP/LTD), navigation map, short-range-static and long-range-dynamic components of the map.

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"We show that synaptic modification during random exploration of an environment shifts the location encoded by place cell activity in such a way that it indicates the direction from any location to a fixed target avoiding walls and other obstacles."


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"It has been shown that a navigational map can be formed by the potentiation of synapses between hippocampal place cells arising from the exploration of an environment (Blum and Abbott, 1996)."

"The difference between the location encoded by place cell activity and the actual location that evokes that activity provides a navigational map directing the animal toward the target from any position in the environment (Blum and Abbott, 1996)."


     - Blum K. I, Abbott L. F. (1996) "A model of spatial map formation in the hippocampus of the rat." Neural Comp. 8:85.93" => OK

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"We show how a long range component of the map, including information about obstacles, develops during random exploration."


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"In the model studied, environmental learning is based exclusively on random exploration that results in chance encounters with both targets and obstacles."



"We begin our analysis by studying how a navigationally useful map can arise from the potentiation and depression of synapses between place cells <<that occur during random exploration of an environment>>."



"For the case of a single target in a simple environment, it is possible to perform a fairly general analysis of the effects of LTP and LTD during random exploration on the encoded population vector."


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"During learning, the synaptic efficacy increases or decreases according to a Hebbian learning rule. This means that the change in the strength of a given synapse is proportional to the correlation of its pre- and postsynaptic firing rates."

"In addition, the change in synaptic efficacy depends on the relative timing of presynaptic and postsynaptic activity. Specifically if presynaptic activity occurs at a time t' and postsynaptic activity at time t, the change in synaptic strength is proportional to a factor H(t-t')."

     J_ij = 

In accordance with experimental results on long-term potentiation we assume that synapses are strengthened, if presynaptic activity precedes postsynaptic firing. Onthe other hand, the synaptic efficacy is depressed if the postsynaptic neuron fires before the presynaptic neuron. We describe the time-dependence of synaptic plasticity by a function of the form

     H(t) =