Mice, like humans, have facial expressions that can reveal their emotional state, according to scientists.
Researchers at the Max Planck Institute of Neurobiology in Germany have identified subtle changes in the face of a mouse when it shows disgust or pleasure, or when it becomes anxious.
The team said the findings, published in the journal Science, could in future allow scientists to develop mouse models to help understand the role emotions might play in mental health disorders or illnesses such as anxiety or depression.
Study leader Dr Nadine Gogolla, a neuroscientist at the Max Planck Institute of Neurobiology, said: “By recording facial expressions, we can now investigate the fundamental neuronal mechanisms behind emotions in the mouse model.
“This is an important prerequisite for the investigation of emotions and possible disorders in their processing, such as in anxiety disorders or depression.”
The researchers recorded the mice as they exposed the lab rodents to sensory stimuli such as sweet and bitter tastes and fearful events like electric shock to the tail or lithium chloride injections.
The team then used machine learning algorithms, a type of artificial intelligence, to identify the facial expressions associated with six emotional responses – pleasure, disgust, nausea, pain, fear and flight.
The researchers said they were also able to measure the relative strength of these emotions.
The team then investigated how the activity of neurons in different brain regions affects the facial expressions using brain imaging techniques.
The neurobiologists were able to evoke different emotional facial expressions when they activated specific brain areas known to play a role in emotional processing.
They found the facial expressions to reflect “the inner, individual character of an emotion” that arise through mechanisms in the brain.
For example, the researchers said mice that tasted a slightly salty solution showed a “satisfied” expression while a very salty solution led to a “disgusted” face.
Dr Gogolla added: “Mice that licked a sugar solution when they were thirsty showed a much more joyful facial expression than satiated mice.”