This lab mouse's eyes tighten as the pain it experiences increases.

Mice grimace in pain just as humans do, say Canadian researchers who have developed a "mouse grimace scale" that could lead to better treatments for people and improved conditions for lab animals.

Laboratory mice are often used in pain research so it is important to get an accurate measurement of their sensation, say psychologists Jeffrey Mogil of McGill University and Kenneth Craig of the University of British Columbia.

"The mouse grimace scale provides a measurement system that will both accelerate the development of new analgesics for humans, but also eliminate unnecessary suffering of laboratory mice in biomedical research," Mogil says in a release. "There are also serious implications for the improvement of veterinary care more generally."

The psychologists say this is the first time researchers have successfully developed a scale to measure spontaneous pain responses in animals that resemble human responses.

Mogil and his team analyzed photos of mice before and while they were in pain. They injected the mice with an inflammatory substance — a common procedure for testing pain sensitivity in rodents — to create pain described as comparable to a headache or an inflamed finger.

Mogil then sent the images to Craig's lab at UBC, where a team of facial pain coding experts used them to develop the scale.

The UBC researchers proposed that five facial features be scored according to the severity of the pain. Those features include eye closing, nose and cheek bulges, and the position of the ears and whiskers.

The researchers say they will now turn to investigating whether the scale works in other species.