Cortical activation during oesophageal stimulation: a neuromagnetic study

Abstract

We investigated the neuromagnetic responses to mechanical stimulation of the oesophagus. In six healthy right-handed volunteers (mean age 31.6 years) the proximal and distal oesophagus were stimulated by electronically controlled pump-inflation of a silicone balloon once every 4.5-5.5 sec (dwell time 145 msec). The balloon volume was adjusted to induce different sensation levels (i) just above threshold of perception, (ii) strong sensation and (iii) painful sensation. Evoked magnetic brain responses were recorded time-locked to stimulus onset with a Neuromag-122TM whole-head neuromagnetometer and modelled as equivalent current diploe (ECD) sources. ECDs were superimposed on individual magnetic resonance imaging (MRI) scans. Magnetic brain responses 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 amplitudes increased. Proximal oesophageal stimulation led to activation of source areas spatially similar to those of distal oesophageal stimulation but with shorter response latencies. Both painful and nonpainful mechanical stimulation of the oesophagus activate the second somatosensory cortex (SII). Evidence for topographic organization of oesophageal afferents in SII is poor.

Functional Magnetic Resonance Imaging (fMRI) and Expert Testimony

“…Recently, the technique has been applied to a number of clinical chronic pain disorders, including fibromyalgia [40,41], chronic low back pain [42,43], and neuropathic pain [44–48], in an effort to define central mechanisms that may contribute to subjective pain symptoms in those disorders. The findings with fMRI parallel other advances in the imaging of brain regions involved in central pain processing that have been made with PET [49–55] and magnetoencephalopathy [36,49,56–62].…”

Cerebral processing of painful oesophageal stimulation: a study based on independent component analysis of the EEG

“…Previous EEG studies also found evidence for early bilateral insular activation. 8 32 In common with the MEG studies of the oesophagus, 30 31 36 we found insular activation shortly before or simultaneously with activation of the sensory cortex in most subjects. This is in agreement with animal studies of anatomical data, suggesting that the insula has an important function for integrating visceral sensory and motor activity together with limbic integration.…”

“…The first MEG based studies found evidence for bilateral activation of the primary and secondary sensory cortex, insula, cingulate, and prefrontal cortex. [28][29][30][31] Previous EEG studies using brain mapping and dipole source modelling of ERPs to mechanical stimulation of the oesophagus found evidence of dipoles close to the cingulate gyrus and insula. [32][33][34] We have modelled the electrical dipoles to painful electrical stimulation of the sigmoid colon.…”

Identification of the optimal parameters for recording cortical evoked potentials to human oesophageal electrical stimulation

“… 31 As the primary somatosensory cortex only receives spinal afferents, where as the insular receives both vagal and spinal afferents, it is likely that oesophageal CEP is mediated by both vagal and spinal afferents and not solely vagal as has been suggested. Furthermore, recent MEG studies 32 , 33 suggest that oesophageal electrical stimulation and balloon distension activate similar regions of the cortex; therefore it is likely that CEP generated by both methods of stimulation are mediated via the same pathways. At present it is not possible to say precisely which fibres are being stimulated using our parameters.…”