Nature Neurosci. doi:10.1038/nn.2140 (2008)

When it comes to neuronal activity, researchers often assume that what holds for anaesthetized subjects holds for those that are fully awake. This simple inference is misguided, Jason Kerr of the Max Planck Institute for Biological Cybernetics, in Tübingen, Germany, and his colleagues have found.

They recorded how pairs of neurons behave in unmedicated rats and how they behave in the same rats when dosed with ketamine. The neuron pairs that generated the strongest correlations in their discharges before the animals were anaesthetized were not those that were most strongly correlated when the rats were drugged.

This means that care must be exercised when extrapolating measurements of firing patterns across populations of brain cells in the anaesthetized to the wakeful.