The featured article is ‘How Do You Feel – Now? The Anterior Insula and Human Awareness’ by A.D.Craig. This is a provocative perspective article in the January edition of Nature Neuroscience Reviews. I call it provocative because Craig gets straight to the point and tells us that the Insular Cortex might just be the seat of consciousness. Craig has been building on the work of William James, James Lange and Antonio Damasio with a fine attention to anatomical detail in developing an influential model of interoception and its relation to the Insular Cortex (I have reviewed 2 of Craig’s previous papers here and here).
Craig identifies a number of studies looking at the relation of the Anterior Insular Cortex to various interoceptive stimuli including heartbeat, gastric distension and pain. He identifies the differential pattern of activation in imaging studies from the anterior through to the posterior Insular Cortex. Craig also identifies a possible role for the Insular Cortex in awareness of body movements (as opposed to a sense of agency for movements), self recognition, speech and various emotions. He also focuses on an ’emotional salience network’ in which the Insular Cortex features. Craig focuses on evidence for the involvement of the Right Anterior Insular Cortex in risk prediction and visual and auditory awareness of the present. There are a number of images from different studies all supporting a role for the insular cortex. He also identifies evidence of involvement of the AIC in time perception, attention and perceptual decision making. Craig also identifies studies implicating the AIC in performance maintenance where it is suggested that the AIC might be involved in the switch from central executive functioning to self-reflective networks. Craig then goes onto look at a theory of the involvement of the ACC in self-awareness and in the process suggests that the AIC should also be included in this regards given the close connections it has with the ACC.
However due caution is needed in interpreting these images as a knowledge of the studies from which they were taken is necessary as well as a closer inspection of the statistical techniques that were used to produce the images.
Intriguingly, Craig goes on to refer to the Anterior Insular Cortex as part of the Ventrolateral Prefrontal Cortex and the Anterior Cingulate Cortex as part of the Medial Prefrontal Cortex. He also identifies an evolutionary theory, in which the ACC and AIC developed independently and then integrated their functioning ot manage autonomic activity. He uses this to explain the close relationship of the AIC and ACC in neuroimaging studies. Craig also looks at other evolutionary and associated evidence suggesting that von Economo neurons are present in maximally in aged humans, less in infants, gorillas, bonobos, chimpanzees and absent in macaques. He then correlates this with self-awareness using the mirror test. Craig also covers the asymmetry of forebrain functions, explaining why this might occur and how this asymmetry might be preserved at the higher level of the Insular Cortex.
Craig then goes onto look at the clinical data commenting on the difficulties of interpreting in this area because of the usual involvement of multiple areas of involvement rather than the Insular Cortex per se. Of interest is one study in which there is a subjective loss of awareness in Frontotemporal Dementia which was attributed by Seeley to the loss of von Economo Neurons.
Craig then develops his theory. He suggests that the AIC contains a representation of the self at each moment in time and acts as a comparator between these points in time. He also suggests intriguingly that this may be interpreted phenomenologically as the ‘Cartesian Theatre’ and that the role of the AIC in predictions may explain the effect that emotions such as anxiety might have on predictions (and I presume this would apply to subsequent thoughts or thought processes e.g. catastrophisation). Craig goes onto suggest as in some of his previous works (and also building on Damasio’s exposition in ‘Descartes Error’ reviewed here) that the Insular Cortex is building a representation of homeostatic function in the body and brain, ensuring the ‘energy efficent’ health of both. Craig then suggest that there is progressively more sophisticated processing from the Posterior through to the Anterior Insular Cortex with the latter being the phylogenetically most recent area. He then goes further identifying a meta-representation of a ‘global emotional moment’ near the junction of the frontal operculum and the AIC where a subjective awareness of self is generated and is able to compare feelings of the past, present and future. He uses this model to explain dilation of time when there is a period of ‘high emotional salience’. Craig then finishes by looking at future directions for research including the need for further neuroanatomical data as well as a number of other questions.
Craig has synthesised the findings from a number of neuroimaging studies. There has been debate recently about neuroimaging study methodology and in the need to examine findings critically. Also fMRI studies are sometimes of small magnitude and require replication. However what is intriguing about Craig’s approach is that even if there is a lot of noise, he has adopted a top-down approach looking at the bigger picture so that even if other studies refute some of the imaging study findings he is able to draw on other studies where the findings might be validated. It will be interesting to see how Craig’s theory of global awareness develops.
Steps To Treatment = 5 (Model with evidence base, further confirmation need, if valid informs treatment approach, informed treatment trialled, incorporation into guidelines if suscessful)
A.(Bud).Craig. Perspectives. How do you feel – now? The anterior insula and human awareness. Nature Reviews. Neuroscience. Vol 10. Jan 2009. 59-70.
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