Figure 3.

Neural signal equivalent circuit in a differential recording setup. Equipotential surfaces (blue dashed curves) and streamlines of the current (blue solid curves) for an electric dipole (white circle) consisting of the current source (+E) and current sink (-E). Each vector (purple lines) references the coordinate system (red lines). $V_{NS\_ME\_DM}$ represents the differential-mode neural signal captured from the electrolyte–electrode interface. Points $S$, $R$, and $G$, respectively, represent the positions of the signal electrode, reference electrode, and ground electrode implanted in the cortex. $Z_S$, $Z_R$, and $Z_G$ represent the path impedances of the signal, reference, and ground electrodes, respectively. Points $P$, $N$, and $G^{\mathrm{*}}$, respectively, represent the inputs of the positive, negative, and differential-mode signal IC ground of the OPA. $I_S$, $I_R$, and $I_G$ represent the path current through the signal, reference, and ground electrodes, respectively. $Z_{OP\_P\_DM}$ and $Z_{OP\_N\_DM}$ represent the equivalent input differential-mode impedance of the positive and negative input of the OPA, respectively. The amplifier shares one negative and one ground input for N recording channels.