The Michigan probe is a class of silicon neural probe developed at the University of Michigan beginning in the 1970s by Kensall Wise and colleagues. Unlike the Utah Array — which has one electrode site per shank — Michigan probes feature multiple recording sites distributed along the length of each shank, enabling simultaneous recording at different cortical depths. This laminar recording capability makes Michigan probes particularly valuable for studying cortical column organization and depth-dependent neural dynamics.
Design
A typical Michigan probe consists of:
- One to four thin silicon shanks (50-100 micrometers wide, 15-50 micrometers thick, 3-10 mm long)
- Multiple electrode sites per shank (8-64 sites per shank, spaced 25-200 micrometers apart along the shank length)
- Integrated signal routing via thin-film metal traces on the silicon substrate
- A connection platform at the base for bonding to external cables or connectors
The probes are fabricated using planar silicon micromachining — photolithography, boron diffusion etch stops, and thin-film metal deposition — a fundamentally different manufacturing approach from the Utah Array's bulk silicon dicing.
Laminar Recording
The key advantage of Michigan probes is the ability to record from multiple cortical layers simultaneously along a single insertion track. Cortical tissue is organized into six layers (L1-L6) with distinct cell types, connectivity patterns, and functional roles. Michigan probes can record from superficial (L2/3), middle (L4), and deep (L5/6) layers concurrently, providing a depth profile of neural activity that is impossible with single-tip-per-shank designs.
Evolution and Impact
Michigan probes evolved into several modern high-density designs. The NeuroNexus company (Ann Arbor, MI) commercialized Michigan probe technology for the research market. The Neuropixels probe — developed by HHMI Janelia, IMEC, and collaborators — extends the Michigan probe concept to extreme channel counts (384-960 sites per shank) and has become the dominant tool for systems neuroscience in animal models. While Michigan probes are primarily used in research rather than clinical BCI, their laminar recording capability has influenced the design of clinical devices.
Comparison with Utah Array
| Feature | Michigan Probe | Utah Array | |---------|---------------|------------| | Sites per shank | 8-64 | 1 | | Number of shanks | 1-4 | 96 | | Depth recording | Yes (laminar) | No (single depth) | | Cortical coverage | Narrow column | Broad surface | | Primary use | Research | Clinical BCI |