Weighting of synaptic responses

Michael Ferber Ferber at zoology.uni-frankfurt.de
Sat Aug 24 00:16:52 EST 1996

In article <4vofut$s8f at reader1.reader.news.ozemail.net>,
   rreich at shell02.ozemail.com.au (Rose Reich) wrote:

>Q: In a modeled neural network the input into a neuron is regulated via 
>   a weighting mechanism. In "real" brains is this performed by regulating
>   Na+ concentration within the dendrite thus changing ion gradient, having
>   a nett effect on the input level at the hillock ? or is it done some other
>   way ?

Fro where does the information about the Na+ come? From my understanding, the 
wheighting or strength of a synaptic connection between two neurones (a single 
neuron can be connected to several hundred or more other neurones) is 
represented in the size of the postsynaptic potential. Changing ion 
concentrations (better activities) in the dendrite of the piostsynaptic neuron 
would affect all inputs in a similar way. 
Nevertheless the strength of a synaptic connection (the amplitude of the PSP) 
may change as a result of a change in the amount of transmitter released by 
the presynaptic cell,  by changing the number of anatomical synapses between 
two neurones which will lead to greater postsynaptic ion-currents, by changig 
the sensitivity of the postsynaptic cell to the transmitter (for exmaple by a 
modification of receptor coupled ion-channels), or by other mechnisms 
(Suggestions are greatly appreciated).  

>Q: How is this weighting controlled? In a modeled neural net one simply 
>   adjusts the weighting vector, but how is this achieved in real brains ?

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