A Low-Capacitance Multielectrode Probe for Use in Extracellular Neurophysiology

A multielectrode structure containing integrated junction-FET input stages is described. Photoengraved microelectrodes are utilized to obtain high dimensional precision, small size, and extremely low capacitive coupling between electrodes. The interelectrode capacitance is less than 0.01 pf. The integrated input devices (JFET´s) reduce the impedance levels on the recording channels to less than 500 ohms, virtually eliminating crosstalk and stray noise pickup from the system. The n-channel JFET´s operate as source-followers from a common 2.5 volt drain supply and have input impedances greater than 100 megohms at 1 kHz. A simple external preamplifier ensures stable operation and easy interfacing with conventional recording and display equipment. Special considerations in the design of low-noise completely integrated input stages for use with metal microelectrodes are discussed in detail. As a result of the low interelectrode coupling in this structure, simultaneous recording and stimulation from closely adjacent areas of brain should be possible with virtually no stimulus artifact.