A multielectrode implant device for the cerebral cortex

A new class of brain implant technology was developed that allows the simul taneous recording of voltage signals from many individual neurons in the ce rebral cortex during cognitive tasks. The device allows recording from 49 i ndependent positions spanning a 2 x 2-mm region of neural tissue. The recor ding electrodes are positioned in a square grid with 350 mu m spacing, and each microelectrode can be precisely independently vertically positioned us ing a hydraulic microdrive. The device utilizes ultrafine, sharp iridium mi croelectrodes that minimize mechanical disturbance of the region near the e lectrode tip and produce low noise neuronal recordings. The total weight of this device is less than 20 g, and the device is reusable. The implant dev ice has been used for transdural recordings in primary somatosensory and au ditory cortices of marmosets, owl monkeys, and rats. On a typical day, one- third of the microelectrodes yield well-discriminated single neuron action potential waveforms. Additional array electrodes yield lower amplitude driv en multiunit activity. The average signal-to-noise ratio of discriminated a ction potential waveforms 6 months after implantation was greater than 9. S imple design alternatives are discussed that can increase the number of ele ctrodes in the array and the depths at which dense array recordings can be achieved. (C) 1999 Elsevier Science B.V. All rights reserved.