  Extracellular recordings of single neurons in primary and secondary
somatosensory cortices of monkeys in vivo have shown that their firing rate can
increase, decrease, or remain constant in different cells, as the external
stimulus frequency increases. We observed similar intrinsic firing patterns
(increasing, decreasing or constant) in rat somatosensory cortex in vitro, when
stimulated with oscillatory input using conductance injection (dynamic clamp).
The underlying mechanism of this observation is not obvious, and presents a
challenge for mathematical modelling. We propose a simple principle for
describing this phenomenon using a leaky integrate-and-fire model with
sinusoidal input, an intrinsic oscillation and Poisson noise. Additional
enhancement of the gain of encoding could be achieved by local network
connections amongst diverse intrinsic response patterns. Our work sheds light
on the possible cellular and network mechanisms underlying these opposing
neuronal responses, which serve to enhance signal detection.
