The synaptic eligibility trace, a concept developed by Alfredo Kirkwood and others, describes how synapses learn to strengthen long-term potentiation based on the precise timing of presynaptic input and postsynaptic response.

“The synapse has learned, 'I need to strengthen long-term potentiation, because there's a presynaptic input releasing typically glutamate onto the postsynaptic cell, the cell that's receiving it and because the order was right, release glutamate, and then respond I should strengthen.”