When a mouse stands in front of the mirror, does it know that it sees itself? Scientists have figured it out and their experiments reveal that it’s quite a complicated story.
Because yes, mice can pass the classic mirror test (see box) with flying colors, but only if a number of strict conditions are met. This can be read in the magazine Neuron.
Classic mirror test
To determine whether animals recognize themselves in the mirror and are therefore aware of themselves, what researchers call the ‘classic mirror test’ is often used. This involves sticking a sticker or making a spot on a part of the body that is impossible for an animal to see without the help of a mirror. And then researchers place the animal in front of the mirror and see whether it makes any attempts to remove the sticker or stain. When an animal does this, it is a strong indication that it recognizes itself in the mirror.
The experiment
For the new research, the scientists collected a number of black mice. They applied a dab of white ink to the mice’s foreheads and then placed the animals in front of the mirror. The mice then began to scrub their foreheads; a sign that they recognized themselves. But – and now it gets interesting – the mice only did this if they had previously stood in front of a mirror, had been in contact with mice that looked like them and if the ink spot was reasonably large.
Ink stain too small
The researchers drew this conclusion after also placing mice with small ink spots (about 0.2 square centimeters in size) on their foreheads in front of a mirror. These mice did not scrub extra hard to clean their foreheads. “The mice require significant external sensory cues to pass the mirror test,” said researcher Jun Yokose. “We have to apply a lot of ink to their heads and because they feel that ink, they are then somehow able to detect that ink on their heads – through their reflection.”
Too little experience
The researchers also experimented with mice that had never seen a mirror. An ink spot was also applied to the foreheads of these mice, after which they were placed in front of a mirror. But these mice didn’t scrub their foreheads. It indicates that some experience with a mirror is required; Without it, the mouse does not pass the classic mirror test.
Social contacts
Because previous studies – with chimpanzees – suggested that social experiences are also required for recognition of the mirror image, the researchers set up another experiment. This time with mice that had lived in social isolation. An ink spot was also applied to the foreheads of these mice, after which they were placed in front of a mirror. And as expected, these mice did not clean their foreheads either. The same applied to black mice, which had only seen white mice during their lives and had therefore never laid eyes on a conspecific that looked like them. It suggests that mice need social experiences with peers who are similar to them to develop the neural networks underlying self-recognition.
Self-awareness
Strictly speaking, after this research you can conclude that mice – under certain conditions – are able to pass the mirror test. And since the classic mirror test is designed to determine whether animals are aware of themselves, you might think that this also proves that mice have self-awareness. But the researchers don’t want to go that far. This is of course partly because so many conditions must be met for a mouse to exhibit behavior that suggests that it recognizes its reflection. According to the researchers, the experiments only show that mice – under certain conditions – are able to detect a change in their appearance. But that doesn’t necessarily mean they are self-aware.
However, the researchers are not done with mice yet. For example, in the future they want to find out whether mice can notice the external change – even if they cannot feel it. As mentioned, the mice felt the large ink spots and that probably helped the mice to subsequently detect the ink via their mirror image. But suppose they don’t feel the external change, can they also notice it through their reflection in the mirror? To find out, the researchers are considering using a technology that is also widely used on social media, where people help themselves to a dog nose or rabbit ears with the help of filters. In a similar way, the researchers could also adjust the appearance of mice – without them feeling anything – before placing them in front of the mirror again. The researchers also want to investigate what exactly happens in the brains of mice when they stand in front of the mirror.
