Reverse-Hebb plasticity leads to optimization and association in a simulated visual cortex

The effects of a variable-phase synaptic modification rule on the experience-dependent development of a simulated visual cortex were investigated. Of interest were the process of optimization of the internal representation with respect to orientation, through which the weakly tuned neurons of visually inexperienced animals attain their tightly tuned adult characteristics, and the process of association by which identical stimuli presented to either eye come to evoke identical cortical representations. In its general form, the synaptic modification rule was Hebbian. However, it was not assumed that positive correlation of presynaptic and postsynaptic activity would lead to an increase in synaptic weight. The relative phase of presynaptic vs. postsynapatic activity that would effect an increase in synaptic weight was a parameter of the modification rule. When this parameter was zero, synaptic modification conformed to the standard Hebbian type. With a value of 180 deg, or the reverse-Hebb condition, negative correlation between presynaptic and postsynaptic activity led to increased synaptic weight. It was found that a synaptic modification rule of the reverse-Hebb type not only optimized the cortical representation, and associated the representations from the two eyes, but was quite stable with respect to retaining the optimized state for long periods of learning.