Frontier: New mechanism for memory consolidation in sleep.

March, 2009

A good night’s sleep may contribute to longer-lasting memories by fine-tuning circuits where memory storage takes place, a new study shows.

Marcos Frank and colleagues at the University of Pennsylvania had shown previously that sleep increases “ocular dominance plasticity,” through which the brain rearranges connections in response to visual stimuli.

In sleeping cats, Frank and colleagues demonstrated that if vision is partially obscured in one eye, neurons in the cortex that normally respond to input from both eyes shift their response to the eye in which vision is clear. “The change was twice as great during sleep, but we didn’t know why,” Frank says.

Reporting in the February 12 Neuron, the investigators show that this sleep-induced enhancement occurs when a type of glutamate receptor, the NMDA receptor, is activated. Also during sleep, neurons in the path of the “open eye” increased production of the proteins that strengthen synaptic connections—structural evidence that this circuit was becoming more robust. An NMDA receptor blocker prevented both of these changes.

When the animals slept, the remodeling, “open-eye” circuits increased their firing rate in tandem with peak NMDA receptor activation.

“Our findings show that after waking experiences, synaptic changes are further strengthened during sleep through the NMDA receptor/protein kinase pathway,” says Frank.