HUMAN SOMATOSENSORY-EVOKED MAGNETIC-FIELDS TO VIBRATORY STIMULATION OF THE INDEX FINGER - IS THERE FREQUENCY ORGANIZATION IN SI

Objective: Frequency organization in the human somatosensory cortex wa s studied, Design and methods: Somatosensory evoked magnetic fields (S EFs) from 12 subjects were measured following vibratory stimulation of the index finger by using a 122 channel whole head SQUID system. Sens ory stimuli comprising a 40 ms vibration at frequencies of 50, 100, 20 0 and 400 Hz were delivered to the volar surface of the tip of the rig ht index finger. Using a singled/pole model, the sources of the magnet ic fields were estimated and mapped onto magnetic resonance images of each subject. The analysis of variance test(ANOVA) was used for statis tics. Results: Source localization was determined on the main two peak s (M60 and M110) of the SEFs. All of the sources were located in the a rea 3b of somatosensory cortex (ST). There were no statistically signi ficant differences between the locations of the dipoles evoked by diff erent frequency stimulations. Conclusions: These results demonstrate t he absence of systematic frequency organization at the hand representa tion area of the SI cortex. We speculate that high frequency vibration above 100 Hz are coded by the fast-spiking interneurons which synapse with Pacinian pyramidal neurons in SI. (C) 1998 Elsevier Science Irel and Ltd. All rights reserved