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Meet Neuropixels: how probes that track hundreds of brain cells at once are revolutionizing neuroscience
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Neuropixels probes are designed to record the electrical activity of hundreds of neurons at once. Credit: Allen Institute
In a bright surgical theatre in central London, neurosurgeon Ahmed Toma makes an incision on the side of a woman’s head. Then, he bores a small hole into her skull, revealing a glimpse of the pink, pulsating brain beneath.
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Toma is preparing to implant a shunt to drain excess cerebrospinal fluid — a routine treatment for a condition called normal pressure hydrocephalus, in which fluid builds up inside the skull. His patient at the National Hospital for Neurology and Neurosurgery (NHNN) has also agreed to take part in an experiment: one that involves briefly placing a centimetre-long probe, thinner than a human hair, into her brain. Called Neuropixels, this probe is designed to record the electrical activity of hundreds of neurons at once.
As Toma and a team of researchers carefully insert the probe into the patient’s brain, Mihaly Kollo, a research scientist at the Francis Crick Institute in London, stands nearby, monitoring a multicoloured array of outputs from the probe’s recording sites in real time. After controlling for electrical noise from the operating table and other surgical equipment, Kollo plays an audio sequence of repeating terms — ‘blind spot’, ‘parking spot, ‘piggy bank’ and so on — to examine how the brain represents the transitions between stimuli, and how they are influenced by frequency and familiarity. As the words ring through the theatre, some trigger brain perturbations that sweep across the waveforms representing the probe’s output — a clear sign that it is picking up activity.
Scientists have long conducted experiments during neurosurgery, which offers a rare opportunity to access a living (and often awake) human brain. But Neuropixels probes might provide researchers with the sharpest view of the organ yet.
Since their debut in 2017, Neuropixels have transformed how neuroscientists do electrophysiology experiments in animals, allowing them to record electrical activity from hundreds, sometimes even tens of thousands, of neurons at once. Over the past year, at the NHNN, which is part of the University College London Hospitals, Kollo and his colleagues have been collaborating with neurosurgeons such as Toma to take Neuropixels recordings in people.
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There are other ways of surveying single-cell activity in large populations of neurons, such as calcium imaging, which tracks the movement of calcium ions that occurs each time a neuron fires. But these techniques can be too slow to capture the action potentials in certain neurons, or require genetically encoded sensors, limiting their use in some organisms and precluding it in humans.