Making sense of the world after birth, let alone navigating it, isn’t something we expect human infants to do.
Baby mice, however, seem to have a leg up on us when it comes to seeing the world with new eyes.
Even before they have witnessed the world around them, a new study suggests newborn mice ‘dream’ of their future.
Imaging the brains of mice pups right after birth but before they opened their eyes, researchers noticed spontaneous waves of retinal activity.
These patterns look remarkably similar to what would occur in its brain if a mouse had its eyes open and was moving forward in its environment.
But these newborns have never seen an environment before, so what are they imagining? And why?
“This early dream-like activity makes evolutionary sense because it allows a mouse to anticipate what it will experience after opening its eyes and be prepared to respond immediately to environmental threats,” explains neuroscientist Michael Crair from Yale University.
To determine just how important these ‘dreams’ of forward motion were to the pups’ visual development, the researchers looked at the role of starburst amacrine cells during early neonatal days.
Starburst amacrine cells are located in the retina and are known to play a part in triggering directional responses in adult mice. They also play a role in retinal development, making them a possible source of these pre-vision waves in pups.
The researchers blocked the functions of the starburst amacrine cells by using a daily dose of a toxin over a two-day period and then analyzed the mice’s waves a few days after the final dose of toxin.
The mice exposed to the toxin experienced significant disruption in retinal wave direction, essentially stopping the creation of those forward-moving motion waves.
Researchers also exposed some of the mice’s retinal ganglion cells – neurons that receive visual information from photoreceptors – to an inhibitor drug called gabazine.
Like blocking the starburst amacrine cells, the gabazine disrupted the creation of the waves.
When both the mice treated with gabazine and those with blocked starburst amacrine cells finally opened their eyes, they experienced degraded abilities to detect motion and directional response actions.
“Overall, these results demonstrate that interfering with the directional bias of spontaneous retinal waves during development compromises the emergence of direction-selective responses in the superior colliculus at eye-opening, highlighting the role of directional retinal waves in the emergence of functional response properties in mice,” the authors conclude.
It would seem that the fundamental circuits of the mouse visual system are formed even before their eyes open. In the absence of any sensory stimulation, the retina merely generates its own spontaneous activity.
“These brain circuits are self-organized at birth, and some of the early teaching is already done,” says Crair.
“It’s like dreaming about what you are going to see before you even open your eyes.”
The study was published in Science.