The Physics of: Ants and Bats

This week's new Weizmann science stories are on ants and bats. Two different models for investigating human behavior? Yes, but not exactly in the ways you might imagine, and so much more than that.

Dr. Ofer Feinerman, the "ant scientist," is a new member of the Physics Faculty. In his graduate research under Prof. Elisha Moses in the Physics of Complex Systems Department, Feinerman created artificial circuits out of neurons. Now he has turned to investigating the complexities of ant societies. What, you might ask, do neurons and ant colonies have to do with physics? The answer is: They involve non-linear, collective phenomena, similar to those studied extensively by physicists. (Moses has investigated everything from falling leaves and advancing wave fronts* to schizophrenia to deep patterns in literature.) So in this physics lab, instead of lasers or ion traps, there are high-tech ant farms where the inhabitants run around with miniature barcodes glued to their backs.

Photo: Lab of Dr. Ofer Feinerman

Of course a huge body of work has already been published on ant social order, and conclusions have even been applied to human society from some of that work. What new perspective will a physicist bring to ant studies? For one thing, Feinerman has the tools - experimental and computational - to conduct in-depth research into one of the basic underpinnings of any society: communication networks. These go beyond the simple divisions of labor: queen, worker, nursemaid, sperm donor, etc, and his studies are already revealing that the ants' social order is both more complex and more flexible than that painted by the more traditional models. Ultimately, it may be the differences between ant and human societies that are the most interesting. Because once a physicist detects a new pattern, he will almost certainly look around for other iterations of that pattern. Understanding how communications help facilitate life in the leaderless ant colonies may not help us to create the perfect anarchist utopia, but it could provide insight into other non-linear networks - for instance complex interrelations between immune cells or communication between swarms of mini-robots engaged in a joint task.

Dr. Nachum Ulanovsky, the "bat scientist" even has a "bat cave" in his lab, where the animals can fly around in the dark. Though he is in the Neurobiology Department, Ulanovsky's research would definitely not be out of place in the non-linear physics lab; and his analytical methods are often borrowed from physics. In fact, in his latest work, he investigated a phenomenon that is more often seen in the neat world of solid-state physics than the messy world of brain biology: cells that fire in an orderly, hexagonal pattern. These cells, called grid cells for obvious reasons, fire as an animal moves through an environment and crosses the vertices of a hexagonal lattice, and they help create maps in the brain.

The question was: What causes this regular firing pattern? Was it due to another non-linear phenomenon - time-dependent oscillations in the same region? Or could the pattern arise from something in the way these cells work together?

Once again, difference was crucial: Researchers who investigated the grid cell patterns in rats and mice had noted that regular oscillations always accompanied their activity. Ulanovsky repeated those experiments with bats, on a hunch that the seemingly solid connection between the spatial pattern and temporal oscillations in the rat brain might come uncoupled in a different animal. Recordings of the activity in this tiny area of the bats' brains showed that the hexagonal firing patterns were there - nearly identical to those of the rats. But, as he and his team reported in Nature several weeks ago, the oscillations they observed were very rare, and did not appear to be tied in any way to the spatial patterns. In other words, the bat's brain has periodicity but it ain't got that "rhythmicity" - which tends to discount the popular theory that the periodicity in the rat's brain is caused by neuronal rhythmicity.

Which brings the whole story back around to communications networks. In this case, the neurons appear to coordinate their activities using the most stable possible network: a honeycomb-like hexagonal grid in which every node is equidistant from its neighbors.

Postscript: Ulanvosky and Feinerman are both locals, and both wrote this science writer that they went to high school together and had the same math and physics teachers. Who says that high school doesn't make a difference?

*The Weizmann Wave banner is a microscope image from Moses' lab of a boundary-layer eruption caused by temperature variations in water.