Tuesday, January 29, 2008

Sleep and the Brain

In some previous posts I linked to recent studies on the importance of a good night's sleep in forming new memories and in reducing the risks of obesity and cancer.

The latest issue of Nature Neuroscience has an article by Vyazovskiy et. al entitled "Molecular and electrophysiological evidence for net synaptic potentiation in wake and depression in sleep". The journal's News and Views piece helps describe the significance of the findings. Here is a sample:

How and why do we spend a third of our lives asleep, and why do even fruit flies do it? Although we have all experienced the poor performance that accompanies inadequate sleep, many aspects of sleep remain mysterious, or at the very least controversial. In this issue, Vyazovskiy et al. provide support for a synaptic view of sleep: namely, that it serves to enforce global homeostatic control of synapse strength, correcting the imbalances created during wakefulness.

...The concept of homeostasis, maintaining a system at a particular set point using feedback modulation, is an old one. More recently, the idea that neurons and neural networks exhibit homeostatic regulation has become an important partner to Hebbian learning rules. Homeostatic plasticity can take many forms, with the regulated set point involving relative synaptic strength, neuronal excitability and/or firing rate. It can also be expressed either pre- or postsynaptically. This broad view of homeostatic plasticity is relevant to the main thrust of the study by Vyazovskiy et al., which shows consistent correlations between molecular and electrophysiological markers of synaptic strength during the early phases of sleep and in wakefulness. Wakefulness increases net potentiation, which is then reduced during recovery sleep. This ensures that the potentiation process can begin anew during the next wake episode.