Freezing ants allows scientists to decipher their navigational system

We’ve heard Coldplay sing “lights will guide you home” but can you imagine a mathematical theorem guiding ants home? Yes, you read it right.

A group of scientists -- Ioannis Pisokas, who is pursuing PhD in Computational Neuroscience and BioRobotics at the University of Edinburgh; Ajay Narendra, a senior lecturer at School of Natural Sciences, Macquarie University; and Ayse Yilmaz-Heusinger, a postdoctoral researcher in Functional Zoology, Lund University – investigated how ants can locate their anthills after travelling long distances in search of food.

Ants travel in relation to the sun’s position in the sky and calculate the distance covered with the help of their own motion. This strategy is called path integration¹ using which ants can locate a point just by knowing the distance travelled and the direction taken.

But how does a tiny insect’s mind identify the right direction and measure the distance?

The researchers dug deeper into an ant’s brain using latest advancements in microscopy and genetics, which enabled them to analyse the working of neurons individually and in relation to other neurons. It was found that ants constantly update their speed in their memory to calculate the distance they have travelled. More surprising is the fact that they retain the memory for several days as “these two aspects of memory – fast updating and long lasting – are typically considered incompatible”².

To understand their memory’s neural network, the scientists decided to anaesthetize ants by freezing them, which disables their brains’ electrical activity. Freezing the ants helped the scientists confirm if memories of distance and direction were stored as short-term electrical activities or long-lasting memories in the insect’s brain.

The scientists picked up ants who were away from their homes and froze them. After a while, they normalized the temperature and released them at an unknown location. The ants immediately figured out the right direction but failed to calculate the distance to their homes.

The result confused the scientists as they couldn’t categorize the memories as short-term or long-lasting. However, they concluded that the distance and the direction form a single memory in the insect’s brain and is partially affected when frozen. Additionally, they have theorized that ants use the Cartesian coordinate system³ to navigate, but the freezing affects this to a great extent. In simple words, suppose that ants know their destination in x-y coordinates. When frozen, they partially lose the memory and the values of X and Y reduce equally, thus changing the coordinates proportionately. As a result, though the sense of direction is correct the distance calculation is affected. As a result, the ants identify the correct direction on the X-Y axes, but fail to calculate the distance correctly.

References:

1. Collett, T. Path integration: how details of the honeybee waggle dance and the foraging strategies of desert ants might help in understanding its mechanisms. https://doi.org/10.1242/jeb.205187

2. The insect brain: we froze ants and beetles to learn how they remember their way home. https://bigthink.com/life/insects-navigation/

3. Cartesian coordinate system. https://en.wikipedia.org/wiki/Cartesian_coordinate_system

4. An Anatomically Constrained Model for Path Integration in the Bee Brain. https://doi.org/10.1016/j.cub.2017.08.052

5. Anesthesia disrupts distance, but not direction, of path integration memory. https://doi.org/10.1016/j.cub.2021.11.039

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