Light Probe Mimicking Slow-Wave Activity in One Hemisphere of Awake Mice Preserved Some Memory Performance

Researchers genetically engineered mice so their neuronal activity could be switched off using light and implanted a light probe into one half of each animal’s brain. The mice were kept awake for five hours by exposure to new objects. Near the end of that period, the probe was turned on and off repeatedly for 30 minutes to mimic NREM slow-wave activity.

After the stimulation ended, the mice were allowed to sleep while brain recordings were taken. The stimulated half of the brain did not exhibit the usual signs of sleep-deprivation exhaustion. Chiara Cirelli at the University of Wisconsin-Madison said that because that small part of the brain did its decluttering while awake, it no longer needed extra deep sleep afterwards.

The same mice were then tested for memory. They first explored a square box with identical carpet texture on both sides for 15 minutes. The animals were assigned to one of three groups: allowed to sleep, kept awake for one hour, or kept awake for one hour with the artificial stimulation.

The next day they returned to the box, now with a new carpet texture on one side. Sleep-deprived mice without stimulation spent similar time on both textures, indicating impaired memory of the original environment. Both the sleep-allowed group and the sleep-deprived-plus-stimulation group spent more time on the novel-texture side.

Cirelli stated that slow-wave sleep activity has been linked to synaptic homeostasis and may be a key mechanism underlying sleep’s restorative functions. NREM sleep constitutes approximately 80 per cent of total sleep time in adult humans. Vladyslav Vyazovskiy at the University of Oxford, who was not involved in the research, stated it should be possible, at least in theory and to some extent, to replicate these results in humans.