A Brief History of Neural Electrode Technology

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Extracellular recording electrodes moved from single metal microelectrodes in the 1950s, to implanted wires that held single units for days and then months, to silicon probes made by integrated-circuit methods from 1970 on. The silicon probes developed at the University of Michigan recorded at many depths at once and, by 2003, recorded in rat cortex for more than six months. NeuroNexus was founded in 2004 to make the Michigan probe available to any laboratory.

Research use only. NeuroNexus products are for non-clinical research use and must not be used in human or veterinary medical procedures.

Metal microelectrodes, 1953–1957#

Our history of microelectrode technology starts in the 1950s.

In 1953, Dowben and Rose described a metal-filled microelectrode: a drawn glass capillary filled with a metal alloy, which recorded single units deep in the brain (Dowben & Rose, Science 1953). In 1957, Hubel ↗ described an electrolytically sharpened tungsten microelectrode for recording single units (Hubel, Science 1957). Tungsten is stiff and does not shatter, so the electrode could be advanced through tissue that would break a glass tip, and it became a standard tool for single-unit recording.

Implanted wires and chronic recording, 1958–1976#

The next step was to leave the electrode in place. In 1958, Strumwasser recorded single neurons over days in unrestrained ground squirrels through implanted fine wires (Strumwasser, Science 1958), one of the first chronic single-unit recordings in a freely moving mammal. Through the 1960s, labs extended the method to behaving animals with bundles of fine wires.

Two problems limited how long an implant lasted: the brain moves relative to the skull, and insulation degrades. In 1973, Salcman and Bak described a chronic microelectrode connected by a fine, flexible lead, so that it moved with the brain instead of being held by the skull (Salcman & Bak, IEEE Trans Biomed Eng 1973). With chronic microelectrodes implanted in the motor cortex of monkeys, Schmidt, Bak and McIntosh reported that 11 of 12 electrodes in one animal recorded single units at some point over 223 days (Schmidt et al., Exp Neurol 1976).

From the early 1970s, the NIH's Neural Prosthesis Program funded much of this engineering, bringing researchers together around neural interfaces and the materials and methods behind them.

Silicon, 1970–1991#

In 1970, Wise, Angell and Starr, at Stanford, reported a microelectrode made by integrated-circuit methods. Recording sites were patterned on a silicon substrate and insulated with silicon dioxide, and the device recorded single units in rat cortex (Wise et al., IEEE Trans Biomed Eng 1970). It is widely cited as the first silicon microelectrode. The method changed what could be designed. A photolithographic process puts each site exactly where the mask places it and repeats that layout on every device, so the number and position of sites became design choices instead of the result of hand assembly.

The work moved with Wise to the University of Michigan, where a group that included David Anderson, Khalil Najafi and Jamille Hetke developed the approach into the multisite probe that became known as the Michigan probe. In 1985, Najafi, Wise and Mochizuki reported a multichannel recording array made with a high-yield process compatible with integrated circuits. Its boron etch-stop sets the thickness of the shank, and it became the basis of the Michigan probe process (Najafi et al., IEEE Trans Electron Devices 1985). In 1988, Drake and colleagues reported single-unit recordings in cortex with planar multisite probes, and showed that closely spaced sites on one shank discriminate single units better than a single site does (Drake et al., IEEE Trans Biomed Eng 1988). Sites spaced along one shank recorded at many depths at once. This is the basis of the laminar array, in which one insertion samples the layers of a structure. In 1991, Kipke, Clopton and Anderson published the first neurophysiological study to use Michigan probes, on groups of neurons in the dorsal cochlear nucleus (Kipke et al., Hear Res 1991).

From the Michigan probe to NeuroNexus, 1994–2004#

From 1994, the NIH-funded Center for Neural Communication Technology at the University of Michigan made silicon probes and distributed them to researchers outside Michigan. Its focus was acute probes, used for one recording session and then removed.

Chronic use was the next question. In 1999, Williams, Rennaker and Kipke characterized the long-term recording performance of wire microelectrode arrays implanted in rat cortex (Williams et al., Brain Res Protoc 1999). In 2003, Kipke, Vetter, Williams and Hetke reported 16-site silicon probes, four shanks of four sites each, implanted in rat cortex: five of six recorded spikes for more than six weeks, and four for more than 28 weeks (Kipke et al., IEEE Trans Neural Syst Rehabil Eng 2003). In 2004, Vetter and colleagues reported that 13 of 14 implanted silicon probes remained functional, with high-quality spike recordings for up to 127 days (Vetter et al., IEEE Trans Biomed Eng 2004).

The mature probe as it stood at that point, its process, shank mechanics, site electrochemistry and chronic assemblies, is described by two of its makers in a handbook chapter (Hetke & Anderson, Handbook of Neuroprosthetic Methods 2003).

In 2004, Daryl Kipke, Rio Vetter, and Jamille Hetke founded NeuroNexus, spun out of the University of Michigan, to make the Michigan probe available to any laboratory. A first-person account of the lineage, and of the design decisions that continue in today's probes, opens Neural Probes: What They Are, How They Work, and How to Choose One.

Timeline#

• 1953: metal-filled glass microelectrode records single units (Dowben & Rose)
• 1957: tungsten microelectrode (Hubel)
• 1958: chronic single-unit recording through implanted wires in a freely moving mammal (Strumwasser)
• 1960s: fine-wire bundles in behaving animals
• 1970: silicon microelectrode made by integrated-circuit methods (Wise, Angell & Starr)
• Early 1970s: NIH Neural Prosthesis Program
• 1973: chronic microelectrode on a flexible lead (Salcman & Bak)
• 1976: single units recorded over 223 days in monkey motor cortex (Schmidt, Bak & McIntosh)
• 1985: high-yield, circuit-compatible process for multichannel silicon arrays (Najafi, Wise & Mochizuki)
• 1988: multisite Michigan probes record single units in cortex (Drake et al.)
• 1991: first neurophysiological study with Michigan probes (Kipke, Clopton & Anderson)
• 1994: Center for Neural Communication Technology distributes silicon probes
• 1999: long-term recording characteristics of implanted wire arrays (Williams, Rennaker & Kipke)
• 2003: the mature Michigan probe described in the Handbook of Neuroprosthetic Methods (Hetke & Anderson)
• 2003–2004: chronic silicon probes record in rat cortex for more than 28 weeks (Kipke et al.; Vetter et al.)
• 2004: NeuroNexus founded

Related documents#

• Where the probe stands today: Neural Probes: What They Are, How They Work, and How to Choose One · NeuroNexus Probe Technology: Questions and Answers · Silicon or wires? Choosing an electrode for multi-channel single-unit recording
• Terms: Michigan probe · Neural probe · Silicon probe · Thin-film microfabrication
• On the site: Our history · Silicon neural probes · Citation database
• Elsewhere: Microelectrode ↗, Microelectrode array ↗, and Single-unit recording ↗ on Wikipedia · Neural Interface Technologies and Applications ↗ in the Nature Index