A measurement system for 256-channel in vitro recordings of brain tissue electrophysiological activity is presented in the paper. The system consists of the brain tissue life support system, Microelectrode Array (MEA), conditioning Application Specific Integrated Circuits (ASIC’s) for signals conditioning, Digitizer and PC application for measurement data presentation and storage. The life support system keeps brain tissue samples in appropriately saturated artificial cerebrospinal fluid at a very stable temperature. The MEA consists of two hundred and fifty-six 40 μm diameter tip-shaped electrodes. The ASIC’s performs amplification and filtering of the 256-field and action potential signals. The Digitizer performs simultaneous data acquisition from 256 channels 14 kS/s sample rate and 12-bit resolution. The resulting byte stream is transmitted to the PC via USB (Universal Serial Bus). Preliminary tests confirm that the system is capable of keeping the extracted brain tissue active (hippocampal formation slices) and simultaneously to record action potentials, as well as local theta field potentials with very small amplitudes from multiple neurons
This paper presents the design and measurements of low-noise multichannel front-end electronics for recording extra-cellular neuronal signals using microelectrode arrays. The integrated circuit contains 64 readout channels and is fabricated in CMOS 180 nm technology. A single readout channel is built of an AC coupling circuit at the input, a low-noise preamplifier, a band-pass filter and a second amplifier. In order to reduce the number of output lines, the 64 analog signals from readout channels are multiplexed to a single output by an analog multiplexer. The chip is optimized for low noise and good matching performance and has the possibility of pass-band tuning. The low cut-off frequency can be tuned in the 1 Hz - 60 Hz range while the high cut-off frequency can be tuned in the 3.5 kHz - 15 kHz range. For the nominal gain setting at 44 dB and power dissipation per single channel of 220 μW, the equivalent input noise is in the range from 6 μV - 11 μV rms depending on the band-pass filter settings. The chip has good uniformity concerning the spread of its electrical parameters from channel to channel. The spread of the gain calculated as standard deviation to mean value is about 4.4% and the spread of the low cut-off frequency set at 1.6 Hz is only 0.07 Hz. The chip occupies 5×2.3 mm2 of silicon area. To our knowledge, our solution is the first reported multichannel recording system which allows to set in each recording channel the low cut-off frequency within a single Hz with a small spread of this parameter from channel to channel. The first recordings of action potentials from the thalamus of the rat under urethane anesthesia are presented.