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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.
There is also communication in the opposite direction between the visual cortex and thalassemia forming a loop of communication between the two structures. 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.
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. If cortex-to-thalamus communication is disrupted in any other behavioral state such as wakefulness, there is no effect on sleep-dependent plasticity of the visual cortex.
But if these oscillatory patterns during slow-wave sleep, you see a deficit, you need these big waves of activity occurring in order to have that benefit of sleep. Researchers made recordings in both a part of the thalamus called the lateral geniculate nucleus, which processes visual information, and the visual cortex of mice.
They tracked the activity of these populations of neurons while presenting the mice with patterns of visual stimulation for hours of subsequent sleep. During visual experience, they discovered immediate changes in the neurons in the thalamus, but nothing going on in the visual cortex. 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.
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