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Rapid mapping of finger representations in human primary somatosensory cortex applying neuromagnetic steady-state responses

Pollok, Bettina; Moll, Marek1; Schmitz, Frank1; Müller, Katharina; Schnitzler, Alfons1 CA

Neurophysiology, Basic And Clinical

We analyzed somatosensory evoked steady-state fields in order to localize finger representations in the hand area of the primary somatosensory cortex (S1). Using a 122-channel whole-head neuromagnetometer we recorded in six healthy subjects neuromagnetic responses to high frequency electrical stimuli delivered simultaneously to digit I, II, III and V at 22, 24, 27 and 30 Hz, respectively, and to transient stimulation of each single digit with a frequency of 3 Hz. Responses were averaged separately for each digit and were modeled by single equivalent current dipoles. Both conditions yielded the typical somatotopic finger representations within S1 hand area. Dipole locations did not differ significantly between the transient and the steady-state stimulation. Therefore, simultaneous high-frequency stimulation of the digits seems to be a reliable method for rapid and detailed mapping of the S1 hand area. This procedure has potential advantages over recording of transient responses. With simultaneous steady-state stimulation the measurement times are reduced to 2 min for mapping the whole hand area. Because of this our method probably increases spatial accuracy and permits repeated short interval recordings, e.g. in experiments studying short term plasticity.

Max Planck Institute for Psychological Research, Munich

1Department of Neurology, Heinrich-Heine-Universität, MEG-Labor, Moorenstr. 5, 40225 Düsseldorf, Germany

CACorresponding Author

Received 28 November 2001 accepted 7 December 2001

© 2002 Lippincott Williams & Wilkins, Inc.