Evidence for a 7- to 9-Hz "sigma" rhythm in the human SII cortex

Electrical activity of the human brain features several rhythmical componen ts which can be readily studied with whole-scalp neuromagnetometers. We de scribe a new 7- to 9-Hz "sigma" rhythm in the human second somatosensory co rtex, distinct from both the mu rhythm of the primary sensorimotor cortex a nd the tau rhythm of the supratemporal auditory cortex. Sigma shows rate-se lective responsiveness to rhythmical median nerve stimulation and is enhanc ed by stimulation at the rhythm's dominant frequency. Single stimuli may tr igger several periods of the rhythm. The functional significance of the sig ma rhythm remains to be investigated. (C) 2001 Academic Press.