A long-term memory forms when

a. neurons send out spikes of electrical activity one time.

b. the same collection or "pattern" of neurons fire repeatedly, forming a neural network.

c. one neuron fires repeatedly

The correct answer is b. the same collection or "pattern" of neurons fire repeatedly, forming a neural network.

Circuits of neurons in the brain, which are called neural networks, are created, altered or strengthened when we learn something. The neural network consists of a number of neurons that communicate with one another through synapses and the transfer of neurotransmitters across the synapse (binding of the neurotransmitter to a receptor), the communicative strength of networks is reinforced. With repeated use, the efficiency of these connections increases.