[Photo by Zhang Zhengyou/Asianewsphoto]

A study of the University of Michigan (UM) has found that visual learning can be cemented in the brain during the deepest part of sleep, called slow-wave sleep.

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. 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, says study author Sara Aton, UM assistant professor of molecular, cellular and developmental biology.

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 deprived of sleep after the experience, no changes in the cortex occurred.

Study also found that if the communication from the cortex to the thalamus during slow-wave sleep is disrupted, it will completely disrupt the slow-wave rhythm and the plasticity in the visual cortex.

"In these mice (tests), during visual experience, we saw immediate changes in the neurons in the thalamus, but nothing going on in the visual cortex," Aton said. "These waves during subsequent sleep are apparently able to transfer information from the thalamus to the cortex, and that information reflects what that animal has just been looking at."

In the next step, the researchers plan to test what types of information can be relayed in this way, and determine exactly how information is relayed to cortex by thalamic neurons.

The study has been recently published in the Proceedings of the National Academy of Sciences.