Figure showing the insular cortex (circled) in a coronal section indicated by the blue line in the inset, Modified from Original Image by John Beal PhD, Dep’t. of Cellular Biology & Anatomy, Louisiana State University Health Sciences Center Shreveport, CC-BY
This is the fourth part of a series looking at building a model of the Insular Cortex, part of the brain that is thought to play an important role in emotions and awareness. ‘In the 2009 paper ‘How Do You Feel Now? The Anterior Insula and Human Awareness‘ Craig outlines an elegant model of the Insular Cortex which integrates neurophysiological findings. In developing the current model, I thought Craig’s model of the Insular Cortex would be a useful starting point for refining the model covered in Part 1 (see Appendix)’*.
Craig has done a lot of work in sensory neurophysiology and uses this as the basis for his model. Reflecting on Craig’s review, I note that it is complex and incorporates reviews of a large number of fMRI studies investigating a vast array of psychological phenomenon. Craig notes that the Insular Cortex is activated throughout many studies investigating disparate phenomenon. Most of the studies considered involve interoception – the awareness of a person’s own body. This includes temperature, movement and body position. Noting the activation throughout such studies Craig draws the conclusion that the Insular Cortex is involved in awareness and has in his work explicitly suggested that the Insular Cortex is a location for consciousness.
Craig’s suggestion is an interesting one. I would propose that consciousness is modular – that is that our conscious experience arises from widely distributed neurophysiological activity in the brain. Furthermore different qualia of conscious experience are physiologically grounded in correlated neuroanatomical regions. For visual consciousness there is the visual cortex and associated areas, for auditory consciousness there is the auditory cortex and so on. Craig’s proposal here is what I would refer to as a top level concept. In a top down hierarchy of concepts – the key concepts that give an overview of the subject area and inform that structure would be at the top of the structure. In building a model it is useful to start off with this approach. The top level concept therefore is that the Anterior Insular Cortex is a key brain area for ‘awareness’ and ‘consciousness’ as it is activated in numerous studies investigating various phenomenon. Other aspects of Craig’s review would then allow the other aspects of this model to be clarified with neurophysiological correlates.
In considering Craig’s model however it is useful to explore alternatives as this helps to shape the model using the theme of the Hegelian Dialectical. In the first instance the suggestion that the Insular Cortex is activated in many fMRI studies does not necessarily imply that it is an important region for awareness. This activation could be an artefact of fMRI methodology. In this regards the authors of one review have suggested that the Insular Cortex plays an important role in processing vestibular inputs. For example this includes the experience of self-motion. In fMRI studies, it has frequently been noted that research participants undergoing fMRI will experience vertigo. Furthermore there is evidence to suggest that the magnetic field inside the MRI scanner stimulates the vestibular apparatus.
Therefore one alternative hypothesis is that the Insular Cortex is frequently activated in fMRI studies as an artefact due to magnetic field stimulation of the human vestibular apparatus with subsequent processing of the sensory input into the Insular Cortex. Although this is unlikely to be the case, consideration of this alternative hypothesis will help to refine the original hypothesis and hopefully make it more robust.
Insular Cortex Resources on this Site
*Text taken from Part 3.
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