  Biological neurons receive multiple noisy oscillatory signals, and their
dynamical response to the superposition of these signals is of fundamental
importance for information processing in the brain. Here we study the response
of neural systems to the weak envelope modulation signal, which is superimposed
by two periodic signals with different frequencies. We show that stochastic
resonance occurs at the beat frequency in neural systems at the single-neuron
as well as the population level. The performance of this
frequency-difference-dependent stochastic resonance is influenced by both the
beat frequency and the two forcing frequencies. Compared to a single neuron, a
population of neurons is more efficient in detecting the information carried by
the weak envelope modulation signal at the beat frequency. Furthermore, an
appropriate fine-tuning of the excitation-inhibition balance can further
optimize the response of a neural ensemble to the superimposed signal. Our
results thus introduce and provide insights into the generation and modulation
mechanism of the frequency-difference-dependent stochastic resonance in neural
systems.
