Oscillatory activity reflects the excitability of the human somatosensory system

The neuronal activity of the resting human brain is dominated by spontaneous oscillations in primary sensory and motor areas. These oscillations are thought to reflect the excitability of sensory and motor systems that can be modulated according to the actual behavioral demands. However, so far, evidence for an association between oscillatory activity and excitability has been inconsistent. Here, we used magnetoencephalography to reinvestigate the relationship between oscillatory activity and excitability in the somatosensory system on a single trial basis. Brief painful stimuli were applied to relate pain-induced suppressions of oscillatory activity to pain-induced increases in excitability. The analysis reveals a significant negative correlation between sensorimotor oscillatory activity, particularly in the alpha-band, and excitability of somatosensory cortices. Oscillatory activity outside the somatosensory system did not correlate with somatosensory excitability. These findings demonstrate that modulations of sensorimotor oscillatory activity specifically reflect modulations in excitability of the somatosensory system and thus provide direct evidence for the basic tenet of an association between oscillatory activity and cortical excitability.