Neuropixels probes

A CMOS shank carrying nearly a thousand recording sites with the amplifiers and multiplexers on the probe itself, which made recording hundreds of neurons at once routine.

The bottleneck in high-density recording was never how small you could make an electrode site. It was wiring. A passive probe needs one conductor per site running out of the brain to an external amplifier, so site count is limited by how many wires the shank can carry and how much tissue that displaces.

Neuropixels moves the electronics onto the probe. The shank is a CMOS process, with amplifiers, filters, multiplexers, and digitisation integrated into the same silicon that carries the 960 recording sites — so what leaves the head is a handful of digital lines rather than a thousand analog ones.

Why that is the whole story

Every hard constraint in the design is a consequence of putting active circuitry inside a brain.

Power, therefore heat. Tissue tolerates very little temperature rise, which sets a budget for the entire amplifier array. Per-channel power has to be small enough that hundreds of channels stay within it, and that budget — not achievable noise performance in isolation — is what determines the front-end design.

Noise within that budget. Amplifier input-referred noise trades against current consumption. The site count is only useful if each channel is still quiet enough to resolve a spike, so the design lives at a specific point on that trade rather than at the low-noise extreme.

Site selection, then multiplexing. The 960 sites feed 384 recording channels, so which sites are live is a programmable choice made by an on-chip switch matrix rather than a fixed wiring pattern — you choose your depth range after the probe is already in the brain. Downstream of that, groups of channels share converters and are sampled in sequence, which leaves a small known skew between channels.

What changed because of it

Recording from many neurons across several brain areas at once stopped being a specialist achievement and became something a normal lab does. That shifted the questions: from what a neuron responds to, toward how activity is distributed across a population and how it evolves over time — the same move microelectrode arrays started, carried far enough to change what most systems neuroscience is about.