Magnetoencephalographic responses to painful impact stimulation

Magnetoencephalographic (MEG) field recordings are unique to detect current dipoles in SI and SII. Few devices are available for painful mechanical st imulation in magnetically shielded MEG rooms. The aim of the present MEG (d ual 37-channel biomagnetometer) study was to investigate the location of th e cortical generators evoked by painful impact stimuli of different intensi ties. An airgun was placed outside the shielded MEG room, and small plastic bullets were fired at the arm and trunk of the subjects in the room. The v elocity of the bullet was measured and related to the evoked pain intensity . Stimuli were delivered for each of the following three conditions: strong pain intensity elicited from the upper arm and upper trunk; weak pain inte nsity elicited from the upper trunk. The evoked MEG responses had a major c omponent with the characteristically polarity-reversal deflections indicati ng a dipole located beneath the coils. The response could be estimated by a single current dipole. When the estimated locations of the dipoles were su perimposed on the individual magnetic resonance images (MRIs), consistent b ilateral activation of areas corresponding to the secondary sensory cortice s (SII) was found. (C) 1999 Published by Elsevier Science B.V. All rights r eserved.