Ž . Brain Research Protocols 4 1999 303–313 www.elsevier.comrlocaterbres Protocol Long-term neural recording characteristics of wire microelectrode arrays implanted in cerebral cortex Justin C. Williams, Robert L. Rennaker, Daryl R. Kipke ) ,1 Bioengineering Program, ECG 202, Box 876006, Arizona State UniÕersity, Tempe, AZ 85287-6006, USA Accepted 29 June 1999 Abstract This paper describes a detailed protocol for obtaining chronic, multi-site unit recordings in cerebral cortex of awake animals for periods of three months or more. The protocol includes details for making relatively simple and inexpensive implantable multichannel electrodes that consist of arrays of separate microwires. The results reported in this paper suggest that a viable implant will have discriminable unit activity on about 80% of the electrodes, resulting in, on average, the simultaneous unit recording of upwards of 60 units during a daily recording session. The active electrodes during one recording session tend to remain active in subsequent recording sessions for several weeks. Using the methods described here, implants have been constructed which incorporate several different electrode materials, coatings, sizes, and electrode separation within a single array. These microwire electrode arrays provide the basic technology for obtaining unit recordings for several months. This provides a model system for studying biocompatibility of neural implants, which is a critical component for the development of neural implants that have an indefinite working span. q 1999 Elsevier Science B.V. All rights reserved. Themes: Sensory Systems Topics: Auditory systems: central physiology Keywords: Microelectrodes; Extracellular recording; Chronic implants 1. Type of research We report a protocol for long-term unit recording in the cerebral cortex of awake animals using permanently im- planted microelectrode arrays. This protocol is relevant to several types of experimental approaches: i. Studies of cortical function, including relationships to w x behavior — e.g., 3,10,14,15,20,22,24 w x ii. Neuroprosthetic research — e.g., 1,2,9,11,18,21 This protocol includes a detailed description of the fabrication of a relatively simple microelectrode array ) Corresponding author. Fax: q1-602-965-0037; E-mail: kipke@asu.edu 1 URL: http:__neurolab.eas.asu.edu. based on microwires. This electrode technology comple- ments alternative existing technologies. w x iii. Silicon Based microelectrode arrays 4,6–8 w x iv. Microwires, including tetrodes 5,12,19 2. Time required The time to make and implant the electrode array depends on experience. After several iterations it is possi- ble to perform the following steps in the time indicated. Ø Make individual electrode rows: 30 minrrow Ø Assemble rows into a complete microelectrode array: 1h Ø Test and clean: 30 min Ø Surgically Implant the Array: 2–3 h depending on the cortical area of interest 1385-299Xr99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S1385-299X 99 00034-3