Any given area in human cortex may receive input from multiple, functionally heterogeneous
areas, potentially representing different processing threads. Alpha (8-13 Hz) and
beta oscillations (13-20 Hz) have been hypothesized by other investigators to gate
local cortical processing, but their influence on cortical responses to input from
other cortical areas is unknown. To study this, we measured the effect of local oscillatory
power and phase on cortical responses elicited by single-pulse electrical stimulation
(SPES) at distant cortical sites, in awake human subjects implanted with intracranial
electrodes for epilepsy surgery. In 4 out of 5 subjects, the amplitudes of corticocortical
evoked potentials (CCEPs) elicited by distant SPES were reproducibly modulated by
the power, but not the phase, of local oscillations in alpha and beta frequencies.
Specifically, CCEP amplitudes were higher when average oscillatory power just before
distant SPES (-110 to -10 ms) was high. This effect was observed in only a subset
(0-33%) of sites with CCEPs and, like the CCEPs themselves, varied with stimulation
at different distant sites. Our results suggest that although alpha and beta oscillations
may gate local processing, they may also enhance the responsiveness of cortex to input
from distant cortical sites.