Chinese scientists have developed an ultralight wireless microscope that can record brain activity in freely moving mice at the level of individual neurons, offering a new way to study how the brain works during natural behaviors.

The device, named Airscope, was developed by researchers from Tsinghua University and the Chinese PLA General Hospital. Weighing just 1 gram, it is more than 30 percent lighter than the latest head-mounted microscopes capable of capturing brain activity across large areas while resolving individual neurons.

Published in the journal Nature on Monday, the research could help scientists better understand the neural basis of intelligence and advance the development of optical brain-machine interfaces, which use light to detect brain signals and could help connect brain activity with external devices.

Airscope has a field of view 6 millimeters wide and can simultaneously record the activity of more than 8,500 cortical neurons in a single mouse — about 25 times as many as previous wireless imaging devices.

Zhang Yuanlong, co-first author of the study and an assistant professor at Tsinghua University's School of Life Sciences and IDG/McGovern Institute for Brain Research, said understanding how the cerebral cortex works during complex behaviors in natural environments is essential to explaining intelligence and developing brain-machine interfaces.

The cerebral cortex, the brain's outer layer, plays a key role in functions such as perception, learning and decision-making. However, studying its activity during natural behavior has long posed a technical challenge: scientists need to observe large areas of the brain in fine detail without equipment that restricts an animal's movement.

Traditional microscopes that can distinguish individual neurons across large areas often require animals to have their heads fixed in place or to remain connected to equipment by cables. Both arrangements can interfere with natural behavior. Wireless head-mounted microscopes allow animals to move freely, but their field of view is typically less than 1 millimeter, limiting observations to a small area of the brain.

To overcome these limitations, the team jointly optimized the microscope's lenses, lighting, electronic components and wireless data transmission. Using just four specially shaped lenses, the researchers built a device that can clearly image individual brain cells across an area spanning 14 regions of the cerebral cortex in one hemisphere.

Wu Jiamin, co-corresponding author of the study and an associate professor at Tsinghua University's Department of Automation, said the device combines wireless operation, low weight, broad coverage and the ability to record the activity of large numbers of neurons simultaneously.

Existing wireless head-mounted microscopes often weigh more than 3 grams, potentially affecting mice's natural movements, Wu said. Airscope is light enough for mice to climb, run and interact socially without being hindered by the equipment.

The device also uses a 2-megapixel image sensor and a data-compression method that reduces the amount of information transmitted by about 25 times. This enables it to send high-resolution images wirelessly in real time while keeping data transmission manageable.

Using Airscope, the researchers conducted experiments that would have been difficult with wired equipment or heavier devices. They recorded brain activity as a mouse explored a 5-square-meter habitat and tracked neural activity in five mice interacting freely at the same time.

In a commonly used tube test, in which two mice compete to push each other out of a narrow tube, a deep-learning model trained on brain activity recorded from two animals predicted which mouse would win with 81.8 percent accuracy, well above the 50 percent expected from random guessing.

Dai Qionghai, co-corresponding author of the study and a member of the Chinese Academy of Engineering, said Airscope provides a new tool for studying brain activity across large areas, complementing the team's earlier RUSH3D system, a tabletop microscope designed to record brain activity in animals whose heads are held still.

Dai, who is also a professor at Tsinghua University's Department of Automation, said Airscope could help optical brain-machine interfaces detect brain signals more precisely. Its potential applications could also extend beyond neuroscience to fields such as immunology and oncology, he added.

The team is working to bring the related technologies into industrial production to help Chinese scientists achieve original breakthroughs using domestically developed scientific instruments, Dai said.