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. Author manuscript; available in PMC: 2009 Oct 30.
Published in final edited form as: J Neurosci Methods. 2009 Jul 21;184(1):142–151. doi: 10.1016/j.jneumeth.2009.07.005

Figure 4.

Figure 4

Both the Fourier-FEM model and the equivalent circuit model reveal the frequency dependent effects of the interface on the stimulus waveform. The circuit model represents the complex impedance of the peri-electrode space and the tissue using a RC circuit for each compartment. In the FEM model, these properties are represented by the conductivity and the permittivity of the regions in the geometry. The electrode is assumed to be perfectly polarisable and is consequently modelled as a pure capacitance. In both cases, the acute interface demonstrates low-pass filtering behaviour, whereas in the chronic stage the effect is mainly a reduction in amplitude. The charge delivered can be measured by the area under the curve, and the FEM model results show that 93% of the charge in the original waveform is delivered in the acute case, but only 76% in the chronic case. In the circuit model these values are 89% and 52%.