Miniature recording probes track brain activity for weeks

Building on the Neuropixel probes released in 2017, researchers at the non profit HHMI Janelia research centre in Virginnia, USA, have developed smaller versions, the Neuropixels 2.0, which are around one third the size. They can track the same neurons inside brains of mice over a period of weeks to study long term brain activities, like learning and memory.

They are designed to record the electrical activity from more individual neurons and can track this activity over extended time periods, even for months. That makes them especially useful for studying long-term phenomena like learning and memory in small animals such as mice, says Tim Harris, a senior fellow at HHMI’s Janelia Research Campus who led the project.

Using imec’s proprietary technology to design, develop, and fabricate the probe, the team have introduced several key innovations which have advanced Neuropixels 2.0, including new ways to process the data. There have also been layout changes to the probes to reduce the size and help them to monitor activity for longer. helped make them better suited to certain tasks. For example in place of a single narrow metal piece that enters the brain in the original Neuropixels probes, the revised versions have four. This distributes the recording sites over a wider area, allowing for more efficient recording in many important brain areas, especially thin layers within the brain, reports the research team.

The probe has a high recording-site density and longterm stability, said Barun Dutta, chief scientist at imec.

Tracking the same neuron is a challenge, because brains move a little bit whenever animals move. Each Neuropixels probe contains multiple recording sites or spots that pick up neural signals. Neuropixels 2.0 has more of these sites which are spaced closer together than the earlier version. This has the same effect as positioning several microphones around a crowded room, the design change makes it more likely that if a neuron moves out of reach of one recording site, it will still be picked up by a neighbouring one. Janelia group leader Marius Pachitariu developed software to track the neurons.

In experiments in mice, the team found they could use two probes to pick up electrical signals from more than 6,000 different sites, says first author Nick Steinmetz, a researcher at UCL and the University of Washington.

Prototypes of the latest version are currently being tested by neuroscientists in labs across the world and being tweaked and fine-tuned in response to users’ experiences. Harris and his colleagues hope that the product will be ready for widespread distribution sometime in 2022.

The Neuropixels 2.0 consortium is led by Tim Harris at the Howard Hughes Medical Institute’s Janelia Research Campus, and includes funding from and scientists at University College London (UCL), at the Norwegian University for Science and Technology (NTNU) in Trondheim, Norway, at Neuroelectronics Research Flanders (NERF) in Leuven, Belgium, and at the Champalimaud Centre for the Unknown in Lisbon, Portugal.

Harris and his colleagues describe the advance in a paper published online April 16 in the journal Science.

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