A low-noise preamplifier for multisite recording of brain multi-unit activity in freely moving animals

A novel FET instrumentation amplifier is described which, as compared to most traditional operational FET preamplifiers, is characterized by an about 7-10 times lower intrinsic electronic noise and a higher common mode rejection. This allows discrimination of single units from multi-unit recording, even if the action potential amplitudes are as small as 20-30 microV and the units are located more than 100 microns away from the electrode tips. Such a distant and chronic recording may be expected to reduce the possibility of mechanical interference with functions of neuronal membrane and its immediate environment, and may be suitable for studying changes in functional connectivities among neurons during the animal's behavior and learning.