We propose a biological cortical column model, at a some mesoscopic scale, in order to better understand and start to interpret biological sources of voltagesensitive dye imaging signal. The mesoscopic scale, corresponding to a micro-column, is about 50 ,m. Simulations are done thanks to the NEURON and NEURONCONSTRUCT software. This model suggests that the OI signal is the result of an average from multiple components whose proportion changes with levels of activity and shows surprisingly that inhibitory cells, spiking activity and deep layers may well participate more to the signal than initially though.