Ultralow - noise headstage and main amplifi ers for extracellular spike recording

This methodological paper provides a detailed description of a novel ultralowABSTRACT noise preand main-amplifi er system designed for the extracellular recording of voltage spikes produced by neuronal action potentials. The main diffi culties with extracellular recording are the unwanted electrical signals that lower the recording quality. They include destructive interferences by alternating electric or magnetic fi elds, in addition to thermal and other random noises resulting from the intrinsic properties of the substances from which the electrode and the electrical circuit are made. The preamplifi er is placed in a specially built metal headstage probe. It is designed so that microelectrodes can be plugged directly into the probe, keeping the electrode and preamplifi er in the closest possible proximity. Unique electrode holder adaptors at the same time make the probe for the electrode holder with the added benefi t of extended electrical shielding. The main amplifi er contains tuned circuit band pass fi lters optimized for metal and carbon fi ber microelectrodes. Electromagnetic interference pickup is reduced by the enclosing tin-plated iron box and a built-in 50/60 Hz reject fi lter. In test experiments, an excellent signal-to-noise ratio and low-noise baseline recording were achieved. When carbon fi ber microelectrodes were applied in the medulla of anesthetized rats, the total peak-to-peak noise level of the system was about 25 μV, i.e., about 6 μV RMS, which is only a few μV higher than the theoretical random noise. It is concluded that, in combination with carbon fi ber electrodes, the present amplifi ers do not contribute signifi cantly to the overall noise. Acta Biol Szeged 48(1-4):13-17 (2004) KEY WORDS