Thursday, March 29, 2007

Beware of the mouse who knows when it is in a trap (or den or nest or bed)

We all know that even a mouse is a tiger in its own den. But for that mouse to become a tiger it must have an awareness of when it is in a den and when it is'nt. Till now, knowledge of abstract concepts like a den or a nest or a bed or a mouse-trap were limited to humans and higher primates. Mice, being such lowly creatures, were not supposed to have abstract concepts and though they may remember a particular den or nest as their own, when placed in a new nest they would supposedly be not aware that the enclosure/ furniture can serve as a nest. To put things simply, they were not supposed to identify objects based on their functionality. If one changed the shape or size of the nest, or the construction material, then they were supposed to get confused and would have not able to still identify the object as a nest or a bed.

All that has become history now, with a new study (pdf) that clearly demonstrates that the mice have abstract concepts in their mind and that specific neurons in the hippocampal area fire when the mouse is in a bed or is entering / exploring one. We already know that we have place cells in hippocampus that fire when a mouse is in a particular location in space and that these are tied to episodic memory. Hippocampus has also been involved in learning mechanisms and it is only appropriate that we discover concept cells in hippocampus that fire when different concepts like bed/ nest/ trap are encountered. And of course we also know of Halle Barre neurons in fusiform gyrus that fire when viewing a particular face.

In this study,the authors found that there were three kind of cells in the CA1 region of the hippocampus, that had distinct firing patterns related to the concept of nests. Whenever a mouse encountered a nest , the transient-on class would increase their rate of firing. If the mouse was not facing the nest, then these cells would not fire; only when the mouse was facing and about to enter the nest were these neurons firing. The second group of neurons were the persistent-on ones, which would fire at a very high rate once the mouse was in the nest and would continue to do so till the time the mouse left the nest. The third type were juts the opposite of these - the persistent- off ones that ceased their normal firing rate, once the mouse entered the nest. Perhaps the rat have not only a concept of nest , but also of not-nest. The base firing of the persistent-off neurons may be a signaling mechanism within the mice brains to indicate that the mice is not in a potentially homely place.

You can read more about the study at the Neurophilosopher (and there you'll also find a great video of a mouse in the study exploring the nest, along with firing neurons) , but what I am amazed is that inst it logical then that the mice also have a concept of a trap - a potentially dangerous enclosure. And whatever variations we may make, isn't it evident that just like we can recognize a trap in its various guises, the mice too can. Making them of wood or metal or of different sizes should not matter. Thus, if the mouse has been exposed to a trap once, there is no use trying to lure it in trap of different type? But maybe I'm just being pessimistic; maybe the lesson we can draw from this study is to make the traps similar to their 'nests', so that they are comfortable and eager to enter in the trap. At long last a study that leads to better mouse traps!


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