By Avigayil Kadesh
They say an elephant never forgets. Well, neither does a bat.
The flying mammals are used in memory research in the lab of Dr. Nachum Ulanovsky, a neurobiologist at the Weizmann Institute of Science in Rehovot.
Ulanovsky explains that a bat’s brain structure is remarkably similar to that of people. Both have a hippocampus, which plays a major role in episodic and spatial memory.
“The hippocampus is an ancient structure,” said Ulanovsky. “It developed long ago, and so is anatomically very similar across all mammals, including bats and humans.”
He is generally interested in using bats to understand how the hippocampus plays a role in neurological conditions such as Alzheimer’s disease, epilepsy and schizophrenia.
He and his researchers published an article about their bat studies in Science magazine that suggests it may be easier to find an object by looking for it indirectly rather than straight on.
Ulanovsky, a pioneer of hippocampus research using bats, works with Egyptian fruit bats, which are common in Israel. This relatively large bat – one of approximately 1,250 bat varieties in the world -- echolocates, using sound to navigate.
Switching senses
The bats in the Weizmann experiments were allowed to fly freely in their climate-controlled room, equipped with tiny backpacks holding the world’s smallest GPS device, which Ulanovsky developed. The bats also got microelectrode implants that measure brain activity and transmit signals via a neural-telemetry wireless recording system developed by Ulanovsky.
When the lights were on, the bats used their eyes to navigate, but when the scientists darkened the room, they switched to echolocation exclusively.
Bats emit slow sonar clicks when they’re searching for a target by echolocation. The clicks become more rapid as they detect the target and prepare to approach it. Ulanovsky found this natural system very convenient, since he “can simply put out a microphone and the animal literally tells you what it thinks.”
The recordings revealed that for some targets, the bats use a focused, high-intensity sound beam, whereas for other targets they use a side-to-side, off-center beam to sweep the area.
Dr. Nachum Ulanovsky at the Weizmann Institute
The GPS data clearly show that bats have some personal preferences. For example, one subject likes to visit a particular fruit tree, passing over others of the same type. Generally, though, their routes are consistently direct and efficient as they find their favorite foods and then return home.
A map-like memory
Previously, Ulanovsky’s bat studies had determined that bats have a large-scale, map-like memory that most likely resides in the hippocampus. He says this was “the first time a cognitive map, which is what enables the bats to navigate, has been shown in any mammal.”
The scientist and his team have published many articles in popular and academic journals about their research – six in 2011 alone.
As reported in their 2008 article “What the bat’s voice tells the bat’s brain” in the journal PNAS (Proceedings of the National Academy of Sciences), Ulanovsky and research partner Cynthia Moss found that the bat's vocal-motor system directly correlates to its spatial orientation by sonar.
Ulanovsky and his group were the first to identify “place cells,” neurons that respond when the animal passes through a certain area of the environment; and “grid cells,” which fire in a remarkable lattice-like or grid-like hexagonal pattern resembling the hexagons of a honeycomb. The findings on place cells and grid cells were published in the prestigious journals Nature and Nature Neuroscience.
The “road map” of a bat’s brain
“Some of the most difficult problems that medicine faces today have to do with the brain,” said Ulanovsky. “I have hope that understanding the function of these memory systems, especially by comparing them across mammalian species, will help solve the dysfunctions that arise. Bats are already generating fresh views on the brain and memory.”