Fig. 1. Schema of the electronic circuitry used as interface between the pairs of Pt microelectrodes and reference electrodes and the multiplexer-data logger assembly. The set of six microelectrodes and reference electrodes connected to the interface includes resistors (R) of 10 x 10⁶ ohms (1%). The seven reference electrodes are connected to ON/OFF switch (S). H1 means high terminal of Channel 1 and L1 means low terminal of Channel 1. H1 COM means high terminal of Common Line 1 and L1 COM means low terminal of Common Line 1 of the multiplexer. 1H1 and 1L1 are the differential channels of the multiplexer sequentially connected to the Common Line 1.