Continuing with the theme of the Insula, the featured paper is ‘Pathobiology of Visceral Pain: Molecular Mechanisms and Therapeutic Implications V. Central nervous system processing of somatic and visceral sensory signals’. This is on the border of psychological papers as it covers phenemonology.
The aim of the paper was to discuss the central nervous system processing of somatic and visceral pain. Implicitly this appears to be at the level of gross activation of brain areas as seen in imaging studies and as such is one of many lines of evidence that are available to examine these phenomenon. The paper summarises imaging studies up to and including 1999.
Curiously there wasn’t a section on methodology for this paper and so it is unclear why the authors selected the papers that they did. Other than this the paper, which is a review paper, was divided into useful sections on the cerebral representation of somatic sensations, angina and enteric stimuli.
In the section on cerebral representations of somatic sensations which forms the bulk of the paper, the authors summarise a number of studies and in terms of the insular identify the following points
(a) Phasic heat pain to forearm activated anterior insula (plus contralateral primary and somatosensory cortex, , Anterior Cingulate Cortex, thalamus and two points within the supplementary motor area. Curiously however another study that was cited didn’t identify the anterior insula although a number of the other regions were found to be activated.
(b) Using a thermal grill illusion which produces hot and cold painful and non-painful stimuli, the insula was activated in response to both hot and cold. The Anterior Cingulate Cortex was instead activated by the painful stimuli alone.
(c) Anticipation of pain activated the anterior insula (in addition to cerebellum and ACC) while pain activated the ‘middle insula’ (as well as the caudal ACC and anterior cerebellum). Anticipation was produced by associating painful stimuli with preceding lights and these therefore produced ‘anticipation’. There is the possibility that they also triggered brain regions by simply providing a visual stimulus in addition to their association with pain however.
(d) Patients with neuropathic pain received a nerve block and in this study it was found that bilateral activation of the anterior insula was associated with pain (as well as posterior parietal, cingulate and prefrontal cortex as well as the cerebellar vermis and right posterior anterior cingulate cortex).
In the section on the cerebral representation of enteric stimuli there were a few studies which suggested involement of the insular cortex. Thus if there was no pain, distension of the oesophagus activated the insula as well as the prefrontal cortex, parietal operculum and parietooccipital cortex. In another study, progressive gastric distension produced a sense of fullness and corresponding insular activation.
The review article is a useful introduction to the activation of brain areas which may be involved in somatic and visceral sensation.
Uri Ladabaum, Satoshi Minoshima and Chung Owyang. Pathobiology of Visceral Pain: Molecular Mechanisms and Therapeutic Implications V. Central nervous system processing of somatic and visceral sensory signals. Am J Physiol Gastrointest Liver Physiol. 279. G1-G6. 2000.
The comments made here represent the opinions of the author and do not represent the profession or any
body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents
of any external sites that are linked to in this blog.