Hebbian Plasticity

• Hebb proposed that if a neuron tends to contribute to the firing of another neuron, the weight from the first to the second will tend to increase.
• He did this in 1949, and it was theoretical instaed of backed up by physiological experiments.
• It fits in with the idea of Cell Assemblies.
• The pithy version of this is neurons that fire together wire together.
• This gives a lot of room for mathematical rules, but these rules can be guided by neurobiological experiments.
• It should be noted that the weight of a synapse can't grow without limit.
• One standard rule is Oja's rule. This makes the weight of the synapses proportional to the probability that the post synaptic neuron fires with the presynaptic neuron.
• Note that timing is important here. How do the neurons tell if they fire at the same time?
• You can also have rules that reduce the weight if the presynaptic neuron does not fire with the post-synaptic neuron.