Final answer:
Long-term depression (LTD) is the synaptic plasticity process that decreases neurotransmitter release after repeated action potentials, making neurons less likely to fire and aiding learning and memory through synaptic pruning.
Step-by-step explanation:
The type of synaptic plasticity that results in a decrease of neurotransmitter release after repeated action potentials is known as long-term depression (LTD). LTD is a process that weakens synaptic connections when calcium enters through postsynaptic NMDA receptors and initiates a cascade that leads to the removal of AMPA receptors from the postsynaptic membrane. This decrease in AMPA receptors renders the postsynaptic neuron less responsive to neurotransmitters, making it less likely to fire an action potential in response to presynaptic activity. LTD plays a crucial role in learning and memory, allowing the brain to prune unused synapses and strengthen important ones.