hebbian learning

Joseph Strout jstrout at ucsd.edu
Wed Sep 13 10:16:05 EST 1995


On 13 Sep 1995, tareq i. j. albaho wrote:

> i have a question concerning hebbian learning	...
> in this model, the connection between two "neurons" is strengthened if
> both neurons are firing, and this leads to learning.
> 
> however, only recently i read that there is no direct experimental
> support for the hebbian model of neural plasticity.

Actually, there is quite a bit of evidence for a Hebb-like learning rule 
in LTP (long-term potentiation); see Brown et al, "Hebbian synapses: 
Biophysical mechanisms and algorithms", Annual Review of Neuroscience, 
13:475-511 (1990) for a review.

The key difference is that actual action potentials ("firings") are not 
required in the postsynaptic cell; rather, depolarization is all that's 
needed.  But this may be a minor point for your purposes.

All forms of LTP seem to depend on an increase in intracellular calcium 
concentration in the postsynaptic neuron.  In NMDA-dependent LTP, NMDA 
receptors (which require both depolarization and synaptic glutamate) 
allow the calcium influx; in non-NMDA LTP, voltage-gated Ca++ channels 
may be involved.

,------------------------------------------------------------------.
|    Joseph J. Strout           Department of Neuroscience, UCSD   |
|    jstrout at ucsd.edu           http://sdcc3.ucsd.edu/~jstrout/    |
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