Period = average time in between spikes (i.e. 0.3s)
Frequency = 1/Period (i.e. 1/0.3s = 3.33 Hz)
Neuron spikes can be represented as an oscillator, with each "lap" around the orbit representing a neuron spiking.
Then, the period of the accompanying sine wave of the oscillator matches the period of the neuron.
Populations of neurons affect behavior. When enough neurons spike in synchrony, a strong enough signal is propogated to affect behavior (i.e. tremor in Parkinson's disease patients).
We can represent a population of neurons as oscillators and observe their synchrony.
Many different factors (i.e. neurotransmitters, upstream neuronal signals, etc.) influence a single neuron's spike. Thus, neurons don't always consistently fire at the exact same rate (and in exact synchrony with other neurons).
Here's how we can represent a noisy population of neurons as oscillators.