Next-generation neural probe leads to expanded understanding of the brain

Neuroscientists are learning new things about how the brain functions thanks to a newly created neural probe with an unparalleled number of micro-LEDs and recording sites combined on the same neural device. The hectoSTAR probe's 128 LEDs and 256 recording electrodes enable neuroscientists to monitor interactions among various brain areas.

Mihály Vöröslakos, a neurologist at New York University and the study's primary author, stated, "With the hectoSTAR probe, we could address several problems that we were not able to answer before." "Being the first to test these gadgets affords a rare opportunity since we have technology that no one else has."

With additional channels, neuroscientists can record not only a larger portion of the brain but also the relationships between various regions, which may provide crucial information for treating neurological illnesses.

The hectoSTAR probe can image an area that extends from the cortex on the outside of a rodent's brain all the way down to the hippocampus in the deep brain. It is equipped with four 30-m thick silicon micro-needle shanks and can record from a region of roughly 1 mm2 (1.3 mm x 0.9 mm) up to 6 mm deep within the brain.

It was developed by University of Michigan researchers for two years before it was successfully tested for the first time in real-world circumstances.

A live mouse's CA3 area of the hippocampus was the location of the hectoSTAR probe. The recording electrodes recorded the neural response as light streamed through one or more LEDs. The researchers found that the light had an effect on the neurons in the CA1 area next to it in addition to the cells next to them in the CA3 region. More over half a millimeter, or 600 microns, separates the CA3 and CA1 areas.

According to Vöröslakos, "using this technology, we may disturb the neuronal system in a highly exact spatial and temporal manner." The hectoSTAR gadget and the tiny LED probe in general are fantastic tools for these research.

It takes time to advance scientific research, as well as frequently a lot of teamwork and collaboration. Vöröslakos spent two years working in Prof. Euisik Yoon's lab at the University of Michigan as a Kavli scholar to make sure the new technology could answer very specific scientific questions. Vöröslakos was already familiar with earlier versions of the brain probe created by Yoon's team there.

Yoon's team published the first-ever neural probe in 2015 that can record activity from many neurons and activate the activity of the neurons with a resolution that is almost single cellular. These probes have 32 recording electrodes and 12 LEDs. By eliminating the significant amount of noise that LED stimulation had added to the recorded neural signal, Yoon's team in 2020—led by former doctoral student Kanghwan Kim (MSE PHD EE '15, '20)—introduced a more useful microLED probe that enables high-quality neural signal recording during LED stimulation.

Yoon stated, "That effort paved the road to scaling it up. "Numerous engineering difficulties had to be solved, but the end product has allowed neuroscientists to better comprehend the global interconnectedness of the brain. This brand-new chip has us quite interested."

With an area of 8 by 11 micrometers, the new LEDs have nearly half the surface area of the previous generation. The hectoSTAR team's chief researcher, Kanghwan Kim, applied theory to produce enough light output to activate the neurons.

When it came to making things smaller, nothing was trivial, according to Kim.

Last but not least, Yoon remarked that raising the number of optical stimulation locations to 128 was a bit of a nightmare. His team created an open-source multi-channel LED controller system to separately regulate the light emitted to each LED and then process the incoming data from the recording electrodes in order to address the control issue.

Yoon explained, "We can carefully select which LEDs are lighted as well as the intensity of the light, which has the capacity to activate only a few neurons nearby the LED, and then record how the signal is travelling to other areas of the brain."

It takes time to double the number of electrodes and LEDs by an order of magnitude. I did had faith that it would work after spending so much time in the cleanroom, said Kim. "Watching those little LEDs come to life was amazing."

"Without it, we would have to insert several probes into the brain to obtain the same data. We were still constrained by the animal's carrying capacity, "Vöröslakos stated.

Vöröslakos is doing more research based on the hectoSTAR electrode's findings and has already requested the devices' upcoming iterations.

In response, Yoon has directed his current research group to develop two crucial improvements to the hectoSTAR: flexible probes and a significantly smaller headstage board. The rat would be able to wander about without restriction and live a long time while having its brain stimulated and recorded thanks to these advancements.

Yoon's lab has previously hosted researchers from other institutions who wanted to learn how to insert his nerve probes and gather data.