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 fifth 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)’*.
In order to build a model of the Insular Cortex i’m following a two step process. Firstly i’m gaining an overview of Insular Cortex function. Secondly when this has been satisfactorily achieved I will fill out the details in the model. Craig covers a lot of ground in his review. Using this as a template is a little tricky but the reason is grounded in the problems facing Neuroscience. Essentially Craig cites numerous studies ranging from basic neurophysiology through to functional Magnetic Resonance Imaging studies investigating specific psychological phenomenon and also includes arguments based on behavioural evolution. An overview of the Insular Cortex necessarily broaches several paradigms and yet this may be necessary in order to gain insights into the emotions. However the structuring of this overview needs to be sensitive to the theoretical challenges posed by linking multiple paradigms.
I’ll focus here on one aspect of Craig’s model – the behavioural evolution of the Insular Cortex. Craig mentions a few things
1. In early mammalian evolution, group behaviour was directed by olfactory stimuli. Mammals cooperated and this group cooperation was driven by smells in the environment. A cursory examination of the footage of Lemurs below shows in some segments the Lemurs overtly smelling parts of the environment. The Lemurs diverged from our ancestors approximately 40 million years ago. Their behaviour can be contrasted with ours and provides supporting evidence for Craig’s assertions. Nevertheless there are other mammal species that demonstrate an even closer relationship between olfaction and behaviour.
2. The Hippocampus and Amygdala are closely related to the Olfactory Cortex both in ourselves and other mammals.
3. In early mammals the Hippocampus and Amygdala would integrate olfactory information
4. The Anterior Cingulate Cortex generated motor actions in response to the output from the Hippocampus and Amygdala
5. The Insular Cortex integrated autonomic activity
6. As behaviours moved away from Olfactory determined group behaviours to individual behaviours interoceptive information became more important in determining behaviour.
7. The Insular Cortex expanded
8. The Insular Cortex and Anterior Cingulate Cortex became linked enabling interoceptive stimuli to generate motor responses through the Anterior Cingulate Cortex
This is a rather simple overview of one aspect of the model. This allows for consideration of further evidence in order to refine the model. The comparative anatomy undertaken by Brodmann may offer insights in this regards.
Insular Cortex Resources on this Site
*Text taken from Part 3.
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