Are cerebral slow waves necessary?

A neurosurgical study of the human somatosensory evoked potential suggested, over 13 years ago, that the early fast waveform recorded by averaging on SI cortex in response to electrical stimulation of the skin is insufficient for a conscious report of tactile sensation. The same study also implied that the succeeding slower waveform, showing consistent averaged timing between 50 and 100 ms after onset of the transient stimulus, was necessary (though perhaps insufficient) for a report of sensation. Since these data seem not to have been denied or confirmed, it may be useful to report hitherto unpublished data on scalp-conducted somatosensory evoked potentials which tend to confirm the direct cortical results, insofar as conventional coherent averages can make any valid contribution to the problem of the sequence of electrophysiological events in laminar cortex when afferent information arrives from the periphery.