EEG oscillations at 600 Hz are macroscopic markers for cortical spike bursts

The human electroencephalogram (EEG) is generated predominantly by synchronised cortical excitatory postsynaptic potentials oscillating at frequencies < 100 Hz. Unusually, EEG responses to electrical nerve stimulation contain brief bursts of high-frequency (600 Hz) wavelets. Here we show, in awake monkeys, that a subset of primary somatosensory cortex single units consistently fires both bursts and single spikes phase-locked to EEG wavelets. Spike bursts were also evoked by tactile stimuli, proving that this is a natural response mode. EEG wavelets at 600 Hz may therefore permit non-invasive assessment of population spike timing in human cortex.