Synaptic Weight Modulation and Adaptation

A “weight” in an artificial neuron model is meant to be a representation of the amount of effect that a synaptic input has on the overall response of the neuron. The neuron that generates the synaptic input (the “action potential” or AP) is called the “presynaptic neuron”; the neuron receiving the effect of the action potential is called the “postsynaptic neuron”. The synapse is the biological structure that connects these two neurons. As such, “the” synapse belongs to neither the presynaptic nor the postsynaptic neuron. The part of the synaptic structure contained within the cell of the presynaptic neuron is called the “presynaptic terminal”. The part of the synaptic structure contained within the cell of the postsynaptic neuron is called the “postsynaptic compartment”. Between these two is a small, liquid-filled gap called the “synaptic cleft.” Transmission from the presynaptic terminal to the postsynaptic compartment takes place by chemical signaling. The presynaptic terminal secretes particular molecules, called neurotransmitters (NTXs), into the cleft. These NTXs bind to receptor proteins on the surface of the postsynaptic compartment, and this chemical binding causes electro-chemical reactions to take place in the postsynaptic cell. Figure 1 illustrates the generic form of a synapse.