How to measure tone of the cerebral cortex? There is a lot of information about the " **tone** of the cerebral cortex". Some scientific papers describe that the tone could decrease or increase. However it's not clear how do they measure the tone of the cerebral cortex. Any ideas? In case if they use EEG for that purpose, could you please specify what exact frequency ranges(alpha,beta,etc.) should have to alter to indicate that the tone is to be decreased or increased? Thank you!

Tonic is used to describe constant muscular contraction; this word has also come to refer to neural activity that leads to constant muscle contraction, and further to mean constant neural activity more generally, in contrast to "evoked" activity produced by some stimulus.

When they say "tone of cerebral cortex" they mean "tonic activity of cerebral cortex", or in other words, they refer to background firing activity at rest/not specifically evoked by some experimental stimulus.

Action potentials are most associated with gamma and high gamma bands, but you can also speak of tone in other bands. It's quite possible they simply mean EEG amplitude. It's not possible to say for sure, you would want to refer specifically to the methods sections of papers mentioning "tone"; they need not all measure the same thing.