It was known that by blocking NMDA receptors, ketamine causes an increase in spontaneous electrical signals, or waves, in a particular frequency range in the brain's cortex, or outer mantle. Hours after ketamine administration— in the timeframe in which ketamine relieves depression — spontaneous electrical activity in people at rest was the same whether or not the drug lifted their depression.
Electrical activity evoked by stimulating a finger, however, was different in the two groups. MEG imaging made it possible to monitor excitability of the somatosensory cortex, the part of the cortex that registers sensory stimulation. Those who responded to ketamine showed an increased response to the finger stimulation, a greater excitability of the neurons in this part of the cortex.
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