For most of us, knowing the way is not a particularly difficult thing, and we humans are excellent navigators who are comfortable navigating different environments. But insect navigation skills are probably better than ours, and even quite amazing.
For example, ants living in the Sahara salt pans can travel more than a thousand meters and know their location to their nests at any point in the journey. On such terrain, there are no landmarks or other features to help ants identify their orientation. Don't forget, a kilometer is almost 120,000 times the length of an ant. This is equivalent to a person walking from Hangzhou to Shanghai, without using any landmarks to be able to clearly understand the correct direction and distance at any time along the way.
For many insects, finding the right direction is almost a matter of life and death. Similar to great human explorers such as Columbus and Magellan, ants knew how to use the sun's position in the sky as a compass and estimate distances by their own motion. This ensures that the ants return to the nest without error after foraging.
When an insect leaves its nest, the direction and distance it travels are encoded by neurons in the brain. To find out how the insect's brain encodes and stores these memories of orientation, a team of scientists conducted very special experiments. They froze some ants and beetles (don't worry, these little guys are still alive). The study suggests that insects may have "harnessed" a system similar to Descartes' coordinate system to help memorize routes. The paper was recently published in Contemporary Biology.
Compatible with different aspects of memory
Thanks to recent advances in microscopy and genetics, scientists have been able to make different kinds of brain cells emit different colors of light. This gives researchers the ability to distinguish individual neurons and unravel the question of how they are interconnected in the nervous system that makes up the brain.
This technique has been used to observe how an insect's brain tracks its direction of action and to identify brain cells that encode the insect's speed as it moves. With this information, insects can continuously add their current speed to their memory over their journey, calculating and tracking how far they have come.
In fact, it's a rather confusing puzzle. Fast-moving insects need to constantly update their memories of direction and distance during their flight, while retaining those memories for days. These two aspects of memory, namely rapid renewal and long-term persistence, are often considered incompatible, but insects seem to manage to combine them.
Frozen insects
To solve this conundrum, in the new study, scientists believe that freezing insects is the best way to find out. This certainly sounds very strange at first glance, but for its own reasons.
Anesthesiologists know that when a person is anesthetized, they forget certain things that happened before anesthesia, but remember other things, depending on how those memories are stored. For insects, the closest state to anesthesia is to temporarily freeze them. When their temperature drops to the temperature of melt ice (0 C), electrical activity in the brain stops and the insect falls into a coma.
If their orientation and distance memories are maintained in the form of short-term electrical activity, those memories are erased when they are frozen. But if they are stored in synapses between neurons as part of long-term memory, then they can still be left behind.
So the scientists caught the ants and beetles as they left their nests, cooled them to 0 C for half an hour, and then put the little guys back into ambient temperatures. Once the ants or beetles have awakened, they will be placed in an unfamiliar place to see what they will do.
Image credit: Pisokas, I. et al. (2022)
Usually, when these insects are released into an unfamiliar place in their living environment, they run straight to where their nests are as if they were not being moved. That is, they move in parallel with their usual path and once they reach the expected distance, they begin to look for an entrance to the nest.
But scientists noticed that the frozen insects would move in the expected direction, but could not remember how far they should have traveled. That is, they will prematurely start looking for an entrance to the nest.
A possible explanation
At first, this conclusion is very confusing, because the memory of their distance is degraded, but the memory of direction is retained. This result did not lead to the clear distinction the team expected between short-term (forgetting) and long-term (reserved) memories.
But the scientists then proposed that the best explanation for this phenomenon is not to see it as two separate memories, but as a common memory, which combines direction and distance to encode together, and after freezing, this memory partially fades.
Think of it this way, the ant does not remember a distance plus a direction (angle), but its position in x-y coordinates, the so-called Cartesian coordinate system.
Insects may have used Cartesian coordinate systems to remember their positions. | Image: Wenwen Wen; Reference: Pisokas, I. et al. (2022)
If it loses some of its memory, both x and y are reduced, and assuming it loses memory in similar proportions on two axes, the final distance will be shortened, but the direction (angle) will still remain the same.
Perhaps, long before Descartes formally proposed the concept, insects had already found their way home using The Cartesian coordinate system.
#创作团队:
Compile: M ka
Typography: Wenwen
#参考来源:
https://theconversation.com/the-insect-brain-we-froze-ants-and-beetles-to-learn-how-they-remember-their-way-home-177763
https://www.cell.com/current-biology/fulltext/S0960-9822(21)01598-0
#图片来源:
封面图：Steve Jurvetson from Menlo Park, USA via Flickr under CC BY
First image: Max Pixel