Utah array (Utah Electrode Array)

The Utah Electrode Array (UEA) is the microelectrode array that has carried most human intracortical BCI work, including the BrainGate trials. It is a monolithic block of doped silicon micromachined into a square grid — classically 10 by 10, with up to 96 to 100 wired channels — of sharpened needles roughly 1 to 1.5 mm long on a 400 µm pitch. Each shank is electrically isolated from its neighbours by a glass moat, insulated along its length with parylene or silicon dioxide, and metallised only at the tip (platinum, iridium oxide, or sputtered iridium), so a single recording site per shank sits near cortical layers 4 to 5.

Because the tips are blunt on the scale of tissue mechanics, the array is inserted with a pneumatic inserter that fires it in under a millisecond, using inertia to defeat cortical dimpling; a slow push simply dents the pia. Signals leave through fine wire bundles to a percutaneous pedestal — the skull-mounted connector — which is the array's defining clinical liability, since it is an infection route and precludes a fully sealed implant.

The UEA's limitations frame much of implant engineering. One site per shank means no depth profiling within a cortical column; the fixed 400 µm pitch and roughly 1 mm length fix which layer is sampled; and the rigid tethered silicon contributes to a foreign-body response and to slow attrition of usable channels over months to years. Newer probes such as Neuropixels and flexible arrays attack exactly these constraints.