The classification of modifiable synapses and their use in models for conditioning

Modifiable synapses are analysed theoretically. It is proved that they fall into three classes (called A, B and C), such that any two members of the same class can, with the aid of non-remembering elements that perform simple logical operations, replace one another in any net; but a member of class A cannot replace one of class B or C. A member of class B can replace one of class A or C only if non-logical elements, for example noise generators, are included in the net. Models are designed that use modifiable synapses and show the principal features of classical and operant conditioning. If the models are to be given the property of extinction, classical conditioning requires modifiable synapses of classes A and B or of class C, and operant conditioning of class B or C. It is argued that if the conditioning and memory mechanisms of the nervous system store information by means of modifiable synapses, some of these must be of class B or C.