A 5376-channel platform mapped signals across the rat cortex

A 5376-channel platform mapped signals across the rat cortex

On August 3, researchers from Rice University and SpikeGadgets described a flexible electrode array and a chip that reads signals from all its contacts simultaneously in a paper in npj Biomedical Innovations. In an acute experiment on an anesthetized rat, the array was placed on the cortical surface and revealed which regions responded to touches on the whiskers, paws, and torso.

A high-density array placed over the brain has two distinct counts. An electrode is a contact pad on the film that touches the tissue. A channel is a separate pathway through which the signal is amplified, digitized, and transmitted. Simultaneous recording makes it possible to compare how neighboring points on the cortex respond to the same touch.

The distinction is illustrated by the BISC wireless cortical surface interface. It has 65 536 electrodes, while its electronics simultaneously read 1024 selected channels. In the Rice system, each of the 5376 contacts is connected to its own channel. Each channel amplifies its signal. A single converter then digitizes signals from four channels in sequence. The system collects 20 thousand samples per second from each input, which produces an outgoing data stream of 1,3 Gbit per second.

The authors tested the system on the surface of the rat's left cerebral hemisphere. They repeatedly touched the whiskers, paws, and torso, then averaged the recordings. Distinct regions of the sensory cortex appeared across a film measuring approximately 7,7 × 9,9 millimeters. The response to an individual touch covered about one millimeter. Surface electrodes record the combined electrical response of many cells, so the experiment shows where these responses occur across the cortex.

The same chip contains 224 addressable stimulation sites, of which 32 can operate simultaneously. The authors tested their pulses using electrical loads, while the cortical map was produced using mechanical touch. Turning a large number of contacts into a synchronous map requires placing amplifiers and converters, connecting the chip to the flexible film, and transmitting the entire data stream to external hardware. In this setup, the data travel through a cable to an external controller.