(Credit: Getty Images)
Certain visual learning takes hold in the brain during sleep, new research suggests.
Remember those “Magic Eye” posters from the 1990s? You let your eyes relax, and out of the tessellating structures, a 3D image of a dolphin or a yin yang or a shark would emerge.
Getting good at seeing those 3D images is an example of visual perceptual learning. Researchers working with mice have found this learning is cemented in the brain during the deepest part of sleep, called slow-wave sleep.
“Magic Eye” image generated from text. (Credit: U. Michigan)
When we see something, our retinas transmit that image to the thalamus in the brain, where neurons send very basic visual information to the visual cortex to be processed, says study author Sara Aton, assistant professor of molecular, cellular, and developmental biology at University of Michigan.
When the brain is awake, neurons in the thalamus and cortex fire steadily to transmit visual information between them. However, in slow-wave sleep, those neurons will burst and then pause rhythmically and in synchrony, Aton says.
There is also communication in the opposite direction—between the visual cortex and thalamus—forming a loop of communication between the two structures.
Prior work in the Aton lab had shown that after presenting mice with a new type of visual experience and then allowing those mice to sleep, neurons in the cortex fired more when seeing that stimuli again. But the lab also showed the brain needs sleep in order to make cortical changes. If mice were sleep deprived after the experience, no changes in the cortex occurred.
“We wondered what would happen if we just disrupted that pattern of activity without waking up these animals at all?” Aton says. “The big finding in our study is that if you disrupt communication from the cortex to the thalamus during slow-wave sleep, it will completely disrupt that slow-wave rhythm and the plasticity in the visual cortex.”
The researchers turned off neurons in the visual cortex that complete the “loop,” sending information back to the thalamus, while the mice were naturally asleep or awake. While this did not wake the sleeping mice, it did keep them from having coordinated rhythms of activity between the two structures during slow-wave sleep.
Aton says if cortex-to-thalamus communication is disrupted in any other behavioral state such as wakefulness or REM, there’s no effect on sleep-dependent plasticity of the visual cortex.