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Nahum Ulanovsky

Two fruit bats in Australia. Photo: depositphotos.com

When neurons change gears: how the brain copes with sudden changes

New research done in bats reveals far-reaching dynamic capabilities of neural networks
Fruit bat. Photo: depositphotos.com

Navigate in a big way

A new neural code for navigating large spaces was revealed in the "bat tunnel" at the Weizmann Institute of Science
Bat news. Photo: Weizmann Institute Press Releases Press Clips for Press Releases Awards and Appointments Institute Visitors Download the "Institute Magazine" application free of charge for iPAD and Android devices Unique tours of the Weizmann Institute of Science Weizmann House Facebook Scientists of the Weizmann Institute of Science measured for the first time nerve cell activity in bats during flight April 18 2013 Neurobiology The findings, obtained using a miniaturized wireless system, provide the first information on how mammals orientate in 24D space ** Dr. Ulanovsky will talk about his research at the "Science on the Bar" event on April 76 (Otto Bar, Ibn Gvirol XNUMX) The ability to navigate and orient oneself in space is necessary for survival - it is what makes it possible to find food and shelter, avoid madmen, and more. A study by Dr. Nahum Ulanovsky and research student Michael Yertzev from the Weizmann Institute of Science, published today (Friday) in the scientific journal Science, reveals for the first time how XNUMXD space is represented in the brain of mammals. The research was done using a unique miniaturized system, developed especially for this purpose, which allows measuring the activity of individual nerve cells during flight. The question of how animals orient themselves in space has been widely studied, but so far only in a two-dimensional context. It is known that there are "place cells", which are nerve cells located in the hippocampus - a brain structure related to memory, and in particular spatial memory. Each of the place cells is responsible for a defined area in space, and sends an electrical signal when the animal is in that area. In this way, all the place cells create, together, a complete representation of the entire space. But in fact, the navigation of many animals, and of humans, is done in three-dimensional space. And yet, attempts to expand the canvas from two dimensions to three encountered difficulties. One of the most prominent attempts in this field was carried out in collaboration between the University of Arizona and the American space agency, NASA. As part of it, rats were launched into space (on the space shuttle). In the end, the experiment did not provide the necessary data since the rats did move in zero gravity in three-dimensional space, but in fact they ran on a linear, one-dimensional track. Other attempts, which used projections of the XNUMXD space onto a XNUMXD surface, also failed. The conclusion was that in order to understand movement in three-dimensional space it is necessary to allow the animal to move in a way that fills all three dimensions; That is, flying animals must be studied. Dr. Ulanovsky chose an Israeli fruit bat - an animal convenient for experiments, and relatively large, so it is possible to connect wireless measurement and recording systems to it, which do not interfere with its free movement. The development effort of the sophisticated measurement system lasted for several years, in cooperation between Dr. Ulanovsky and a commercial company in the USA. In the end, a wireless, light system was obtained (weighing 12 grams, about 7% of the bat's weight), with electrodes that measure the activity of individual nerve cells in the bat's brain. Another challenge faced by the scientists was to adapt the behavior of the bats to the purpose of the experiment. Naturally, the bats fly to their destination - for example, to the fruit tree - in a straight line, i.e. in a one-dimensional way, whereas for the purpose of the experiment they had to fly freely so that they fill a three-dimensional volume. The solution to the problem is found in a previous study by Dr. Ulanovsky, in which he followed fruit bats in the wild using miniature GPS devices and discovered, among other things, that when the bats reach the fruit tree, they circle it and move in a way that fills the entire space around the tree. To simulate this situation in the laboratory - which is a kind of artificial cave equipped with equipment for full monitoring of the bats - an artificial "tree" made of metal rods, to which bowls of fruit are attached, was installed. Measuring the activity of nerve cells in the bats' hippocampus showed for the first time that the representation of XNUMXD space in the brain is similar to a XNUMXD representation: each of the place cells is responsible for identifying a specific area in the "cave" space, and sends an electrical signal when the bat enters this area. The entire population of place cells forms a full coverage of the entire "cave" volume. A careful examination of the areas for which the place cells are responsible provided a solution to a controversial question - is there "equality" in the perception of the three dimensions, for example, is the resolution of the perception of height in the brain the same as that of length and width. The findings show that the area each of the place cells is responsible for is spherical, meaning that the resolution is indeed uniform in all three dimensions. The researchers point out that it is possible that in non-flying animals, which actually move in a flat space, the level of resolution in the different axes is not uniform. It is possible, for example, that such animals should be more sensitive to changes in the axis of length and width, and less to changes in the axis of height. Regarding humans, this is a particularly interesting question, since on the one hand they evolved from monkeys that jump in three-dimensional space, from branch to branch, but on the other hand, their characteristic movement is in two-dimensional space. The research findings provide new insights into the basic functions of the brain: navigation, spatial memory, and spatial perception, and this is largely thanks to the development of the innovative technology that made it possible for the first time to glimpse the insides of the brain of a naturally flying animal. Dr. Ulanovsky believes that in the long term, brain research will turn to natural research as much as possible, that is, it will investigate the brain basis of animal behavior in laboratory facilities in which the conditions in nature are imitated, or even when they are found in their natural environment, while performing natural tasks. Israeli fruit bat. Photo: Dr. Yossi Yuval/Weizmann Institute for Israeli Fruit Bat Science.

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