If presynaptic action potentials impinging on a postsynaptic neuron, with long intervals between each action potential, fail to stimulate the p ostsynaptic neuron to produce action potentials, but those with shorter intervals between each action potential succeed in activating the postsynaptic neurons to produce action potentials, which of the following most likely occurred? a. spatial summation
b. temporal summation
c. presynaptic inhibition
d. inhibitory postsynaptic potentials