Neuropixels probes, which can record electrical activity from hundreds or thousands of neurons at once, are giving scientists an unprecedented view of brain activity. Originally developed for animal research, the technology is now being adapted for use during human neurosurgery, while newer versions are helping researchers map neural activity across entire brains in mice and non-human primates.
In a brightly lit operating theatre in central London, neurosurgeon Ahmed Thoma makes an incision in a woman’s scalp and drills a small hole in her skull, revealing the pink, pulsating brain beneath.
Thoma is preparing to implant a shunt to drain excess cerebrospinal fluid. The procedure is a routine treatment for normal-pressure hydrocephalus, a condition in which cerebrospinal fluid accumulates inside the skull. His patients at the National Hospital of Neurology and Neurosurgery (NHNN) have also agreed to take part in a research experiment involving the brief insertion of a centimetre-long probe thinner than a human hair.
The probe, known as a Neuropixels probe, is designed to record the electrical activity of hundreds of neurons simultaneously. As Thoma and his team carefully insert it into a patient’s brain, Mihai Kolo, a research scientist at London’s Francis Crick Institute, monitors the colourful output from the recording site in real time.
After accounting for electrical noise from operating tables and surgical instruments, Kolo plays sequences of repeated terms such as “blind spot”, “parking lot” and “piggy bank”. The researchers are examining how the brain represents transitions between stimuli and how those responses are affected by frequency and habituation. As the words echo through the operating theatre, some trigger disturbances that spread across the probe’s waveform, indicating neural activity.
Scientists have long conducted experiments during neurosurgical procedures, which offer a rare opportunity to study the living, and often conscious, human brain. Neuropixels probes could provide researchers with one of the clearest views yet of activity in the organ.
Since their debut in 2017, Neuropixels probes have transformed electrophysiology experiments in animals by allowing researchers to record electrical activity from hundreds or even tens of thousands of neurons at once. Over the past year, Kolo and his colleagues at NHNN, part of University College London Hospital, have worked with neurosurgeons such as Thoma to use the probes in people.
Recording many neurons at once
Other methods for studying activity in large populations of individual neurons include calcium imaging, which tracks the movement of calcium ions that occurs when a neuron fires. These techniques can be too slow to capture the action potentials of individual neurons, however, and they require genetically encoded sensors, limiting their use in some organisms and ruling them out for studies in humans.
In humans, researchers have primarily relied on devices placed on the brain’s surface to measure activity across populations of neurons, including high-density electrocorticography. Tools such as the Utah array have also enabled single-cell recordings from relatively small numbers of neurons. The Utah array is a small device covered with tiny needles that penetrate about 1 millimetre into the brain and provide 96 recording channels.
Pierre Bourdillon, a neurosurgeon at the Adolphe de Rothschild Foundation Hospital in Paris, compares the advance made possible by Neuropixels with the difference between trying to decipher a conversation using a single microphone at a busy intersection and listening with individual microphones attached to each speaker’s collar.
“We’re just starting to get to the level of microphones to individuals,” he says. “For non-human animals, this revolution started about 10 to 15 years ago. We are now just beginning to see the first teams using this type of technology in humans.”
Simultaneous recording
A short walk from NHNN, in a hospital converted into a research facility known as the Cross Building at University College London, neuroscientist Matteo Carandini is applying an advanced version of Neuropixels technology to animals with much smaller brains.
His team has used Neuropixels probes to record tens of thousands of neurons in mouse brains, sometimes for months at a time. On a sunny Monday afternoon in September, he demonstrated the Neuropixels Opto system.1 The version of the technology that he helped develop combines electrical recording with optogenetics, a method that uses light to switch neurons on and off.
Neuroscientists Hayley Bounds (left) and Matteo Carandini examine Neuropixels data. Credit: Matteo Carandini and Hayley Bounds
Carandini was one of the first neuroscientists to use Neuropixels, a device originally designed for rodent research. The project began with Tim Harris, a biomedical engineer who joined the Howard Hughes Medical Institute’s Janelia Research Campus in Ashburn, Virginia, in 2008. His task was to identify and develop tools that researchers needed.
When Harris asked his colleagues, “What do you want to measure that you can’t?”, he found that they lacked probes capable of supporting large-scale, long-term electrophysiology experiments. In living animals, researchers need to measure the electrical properties of neurons directly.
At the time, scientists primarily used arrays of twisted four-wire electrodes, which could be combined to record from dozens of channels, or silicon probes that typically had about 32 recording sites. Researchers wanted a more comprehensive picture of how brain cells work together to perform the organ’s vital functions. That required recordings from many more neurons.
After testing some designs himself, Harris contacted the Interuniversity Microelectronics Center (Imec), a research institute in Leuven, Belgium, that contributed to the development of advanced microchips. To Harris’s surprise, Varun Dutta, principal scientist at Imec’s Semiconductor Technology and Systems Center, agreed to take on the project.
Together, they developed Neuropixels 1.0. The silicon probe has 960 recording sites along its hair-thin shank. Each channel is small enough to capture the action potentials of individual neurons, and 384 channels can be read out in parallel. The shank is attached to a chip roughly the size of a nano-SIM card that contains the electronics needed to read, amplify and digitize the signal. The output can be transmitted using just two wires, a major advance over devices that required a separate wire for every recording channel.
In a paper reporting the technology,2 Carandini and about 30 neuroscientists from multiple laboratories showed that two probes, each weighing about 250 milligrams, could be inserted into a mouse to record about 700 neurons simultaneously across five brain regions.
Neuropixels 2.0, a small, lightweight probe with four shanks, was introduced four years later.3 It has 5,120 recording sites, 1,536 of which can be read out at once. The 1.0 and 2.0 probes are available from Imec for approximately $1,700 and $1,800, respectively.
Carandini says Neuropixels probes have changed how neuroscience is conducted. His team uses them to study how the brain processes and uses sensory signals, tracking individual action potentials from thousands of neurons at once across multiple regions of a mouse brain that is only about a centimetre long.
Using Neuropixels, researchers have found that signals associated with particular sensory, cognitive and motor functions are more widely distributed across the brain than previously thought.4 The probes have also enabled scientists to study neural manifolds: distinctive patterns of activity that emerge within populations of brain cells.
In several collaborations known as Brain Observatories, independent teams have conducted the same experiments using standardized methods and collected large Neuropixels data sets. In a 2025 study,5 more than a dozen laboratories in the United States and Europe, working as the International Brain Institute, recorded activity from more than 620,000 neurons across 279 regions in 139 mice. The result was a brain-wide map of neural activity associated with cognitive and motor functions, including vision, movement and decision-making.
From rodents to humans
Approximately 1,700 laboratories around the world use Neuropixels probes in more than 24 species, including zebra finches, bearded dragons and octopuses. “I was completely surprised that the researchers used these in different species,” Harris says.
Scientists studying non-human primates were especially enthusiastic. Their existing tools either had too few recording channels or could access only the brain’s superficial layers. Harris, Dutta and their colleagues worked with the research community to develop Neuropixels 1.0 NHP.6
The device has a thick shank designed to penetrate the tough membrane surrounding the non-human primate brain. It is 4 centimetres long, allowing it to record from deeper structures. According to Dutta, the probes cost about $4,200 each.
Before Neuropixels, researchers could record from about 24 neurons in non-human primates “on a sunny day”, says Tyryn Moore, a neuroscientist at Stanford University in California who worked on the project. It is now routine to record from at least 100. Without these tools, primate neuroscience “would still be in the dark ages”, he says.
Moore and his colleagues plan to use the NHP probe to create high-resolution maps of neural activity in the macaque visual system as part of the Enigma Project, a brain-recording and deciphering initiative based at Stanford University.
The Neuropixels probe records brain activity during surgery to remove part of a person’s brain. Credit: Mihaly Kollo/UCLH
Source: www.nature.com