Cortical activation during oesophageal stimulation: a neuromagnetic study

We investigated the neuromagnetic responses to mechanical stimulation of th e oesophagus. In six healthy right-handed volunteers (mean age 31.6 years) the proximal and distal oesophagus were stimulated by electronically contro lled pump-inflation of a silicone balloon once every 4.5-5.5 sec (dwell tim e 145 msec). The balloon volume was adjusted to induce different sensation levels (i) just above threshold of perception, (ii) strong sensation and (i ii) painful sensation. Evoked magnetic brain responses were recorded time-l ocked to stimulus onset with a Neuromag-122TM whole-head neuromagnetometer and modelled as equivalent current diploe (ECD) sources. ECDs were superimp osed on individual magnetic resonance imaging (MRI) scans. Magnetic brain r esponses following distal oesophageal stimulation were adequately explained by a time-varying 2-4 dipole model with unilateral or bilateral sources in second somatosensory cortex and later sources in the frontal cortex. With increasing stimulus intensities, latencies of the sources decreased and amp litudes increased. Proximal oesophageal stimulation led to activation of so urce areas spatially similar to those of distal oesophageal stimulation but with shorter response latencies. Both painful and nonpainful mechanical st imulation of the oesophagus activate the second somatosensory cortex (SII). Evidence for topographic organization of oesophageal afferents in SII is p oor.