Brain research goes wild

By Anne Sperling

Off the coast of Tanzania in the Indian Ocean sits Latham Island, a tiny, uninhabited coral landmass attracting breeding seabirds, nesting turtles—and now, Weizmann neuroscientists fascinated by the brain’s navigational system.

Prof. Nachum Ulanovsky, from the Department of Brain Sciences, has already put himself on the international map of “who’s who” in neuroscience through his groundbreaking work to understand how Egyptian fruit bats—native not only to Africa, but also to Israel— navigate across vast distances. His experimental set-up on the Weizmann campus in Rehovot includes a 700-meter-long bat tunnel—the first of its kind in the world—and a spatially complex maze structure the size of a football field.

By mounting a tiny neural recording device (the Ulanovsky team’s own innovation, the “Neurologger”) on the bats’ heads, the group is able to record the activity of individual neurons in the hippocampus of the bats as they fly freely in the tunnel or the maze.

The hippocampus is home to the brain’s inner map and compass and is responsible for memory storage, including spatial memory. This brain region is also the first to be affected by Alzheimer’s disease, which explains why one of the first symptoms is difficulty navigating in one’s own neighborhood.

Now, long tunnels and intricate mazes are wonderful for studying one- and two-dimensional navigation—but of course, we live in a 3D world. Prof. Ulanovsky struggled for years to come up with a solution for cracking the third dimension over large geographical scales. And that’s not to mention the other issue: how to ensure that the Neurologger-wearing bats will fly sufficiently far to generate usable data and yet will not escape if allowed to fly completely unrestricted—that is, if they fly outdoors, outside any enclosure.

“I was at a conference in Australia in 2018 and went scuba diving on an island in the Great Barrier Reef when I had this revelation: the solution was an uninhabited, isolated island in the ocean somewhere,” recalls Prof. Ulanovsky.

Indeed, a remote island in the middle of the ocean makes it easier to catch the bats and ensures they won’t escape, as there is nowhere to go. And the small size of such a hypothetical island would ensure that the bats could fly multiple times around the same region, providing rich datasets.

Island paradise

After searching the Pacific, Prof. Ulanovsky ultimately discovered the potential of Latham Island in the Indian Ocean, off the coast of Tanzania—home to the same species of bat that his team studies in Israel. In 2022, the Ulanovsky group received permission to rent a building from the Central Veterinary Authority of the Tanzanian government, on the mainland, which the team then renovated. The six-room lab includes animal care facilities and a flight-test space. After fitting the bats with Neurologgers, the team sails with them to Latham Island to carry out the outdoor field experiments.

The Weizmann team—including senior staff scientist Dr. Liora Las, veterinarian Dr. Avishag Tuval, postdoctoral fellow Dr. Saikat Ray, PhD student Shaked Palgi, and research assistant Chen Cohen—has already conducted fieldwork there twice—in 2023 and 2024. Each time they go—usually for 1-2 months— they need to catch a new cohort of bats, acclimate them to human contact, fit them with Neurologgers, and then sail to the island. There, the bats are released to fly around while their brain activity and GPS-based positions are recorded using the Neurologger. The scientists must also set up camp on Latham Island: They sleep in tents or in hammocks—making it quite an outdoorsy experience.

“I was at a conference in Australia… when I had this revelation: the solution was an uninhabited, isolated island in the ocean somewhere,” says Prof. Nachum Ulanovsky.

“I like camping, so for me the whole ‘Robinson Crusoe’ scenario was fun, but combining this with cutting-edge neuroscience was intense,” says Shaked. “Making sure our equipment and electronics could work under all kinds of crazy weather and field conditions, improvising procedures on the fly, waking up in the middle of the night to move our tents due to rising sea levels—it was exciting to remember that the data we were collecting is unique— no one else in the world has ever done this!”

Local collaborators include Dr. Julius Keyyu, a lead scientist from the Tanzania Wildlife Research Institute, and Dr. Abdalla Ibrahim from the State University of Zanzibar, who helped them with the permitting process. And then there’s Jason Alexiou, a local sportfishing legend who shuttles the researchers and their supplies between the mainland and the island.

3D science

What makes this work so compelling is that it’s the first time anyone has been able to record activity from individual neurons in freely behaving mammals as they navigate in 3D.

Bats, like all mammals, exhibit “head direction” cells in their hippocampus—neurons that become more active when the animal’s head points in a specific direction. Unlike rodents, whose head-direction cells are only sensitive to two dimensions, bats’ head-direction cells operate in 3D—at least, in the lab they do. But what happens in the real world, with real, rotating landmarks, such as the Moon and stars (and not artificial substitutes)? Prof. Ulanovsky is finally able to answer this question with bona fide evidence, as well as explain how “goal direction” is represented in the brain, among many other lines of inquiry.

The intensive fieldwork on a remote oceanic island complements the team’s longer-term studies done on campus in the bat tunnel and the bat maze—creating a holistic understanding of the neural mechanisms of navigation.

“This isn’t just the first time someone has done 3D, single-neuron studies in bats,” Prof. Ulanovsky emphasizes. “It’s the first time that anyone has recorded neurons in the brain of any mammalian species in an outdoor environment.”

NACHUM ULANOVSKY IS SUPPORTED BY:

• Irene and Jared M. Drescher Center for Research on Mental and Emotional Health
• Barbara and Morris L. Levinson Professorial Chair in Brain Research
• The Ben B. and Joyce Eisenberg Foundation Research Fellow Chair in Neuroscience supports a Staff Scientist in Prof. Ulanovsky’s lab