Spending hours preening in front of the mirror might be a sign of vanity in humans.
But for mice, it may be a sign of self-awareness.
Just like humans and chimps, mice are able to recognise their own reflections in a mirror, according to a team from the University of Texas.
Scientists found that mice who had been daubed with white ink were able to spot themselves in a mirror and try to clean themselves up.
This means that mice pass the ‘Mirror Test’ – a standard often believed to be a sign of self-awareness or consciousness in animals.
Researchers found that mice who had been socialized and were used to mirrors were able to pass the ‘mirror test’ – often believed to be a sign of self-awareness
The researchers painted the heads of mice with white ink to see if they could recognise their reflections in a mirror
In the study, the researchers anaesthetised several black mice and painted their heads with different-sized spots of white ink.
The mice were then placed in front of a mirror.
The researchers’ obsevations revealed that mice with the white marks would spend more time grooming in front of the mirror, suggesting that they have the ability to recognise themselves.
This was only the case under specific circumstances, however.
The mice would only try to remove the ink when the spot was fairly large and when it was a different colour to their fur, which suggests they were actually seeing that something was different about their appearance.
They also only tried to clean off the ink if they had spent time around mirrors in the past and had been raised around mice that looked like them.
Black mice that were raised around white mice seemed to lose the ability to recognise their reflection, suggesting that socialization plays an important role in developing a self-image (stock image)
This image shows the neurons in the hippocampus which scientists believe play an important role in developing self-image
For example, only black mice that had been raised around other black mice appeared to have the ability to recognise their own reflections.
Black mice who were isolated after weening or raised in the company of white mice didn’t try to remove the marks from their head, even when they were the right colour and size.
The researchers say that this proves that self-recognition and self-awareness must have a social element.
To understand this effect further, the researchers used brain scans to analyse the animals’ brains as they looked in the miror.
The scans revealed that a set of neurons in the hippocampus – a structure deep in the brain – were activated when the mice saw themselves in the mirror, as well as mice who looked similar.
Mice who had this region de-activated were unable to recognise themselves.
The researchers suggest that without socialisation. these neurons fail to develop, leading to a lack of self-recognition.
Senior author Takashi Kitamura, from the University of Texas, said: ‘To form episodic memory, for example, of events in our daily life, brains form and store information about where, what, when, and who, and the most important component is self-information or status.’
The authors say that this doesn’t prove that mice are self-aware but does show that they have the ability to recognise themselves
The mirror test has previously been used to assess consciousness in a number of different animals, including chimpanzees, dolphins and elephants.
However, the researchers are careful to say that this does not prove mice are self-aware.
Instead, what the data shows is that mice have the ability to recognise themselves under certain circumstances.
Lead author Jun Yokose, of the University of Texas, said: ‘The mice required significant external sensory cues to pass the mirror test—we have to put a lot of ink on their heads, and then the tactile stimulus coming from the ink somehow enables the animal to detect the ink on their heads via a mirror reflection.
‘Chimps and humans don’t need any of that extra stimulus.’
This research was published in the journal Neuron.
