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How the brain makes us feel

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Bud Craig’s 2009 paper: How do you feel—now?  The anterior insula and human awareness brings together findings of numerous authors in a discussion of functional imaging of the anterior insular cortex (AIC) and the starring role it plays in human awareness.  The groundwork for this recent Perspective, and arguably for much of the research in the field, was laid by Craig himself back in 2002 when he discussed interoception—our sense of the physiological condition of our physical body [1].

I found Craig’s paper concise, well structured and refreshing.  The AIC and its function have always been a bit of a grey (for want of a better word) area for me.  So has the anterior cingulate cortex (ACC) and its widely reported joint activation with the AIC.  I thought I’d share with you the points in this paper that I found most interesting, or those that cleared up for me a previously confusing area of neuroscience…

Interoceptive information—information about the internal state of the body—is integrated in a posterior-to-anterior pattern in the insula.  For instance, when we experience a decrease in body temperature this evokes activity in the posterior insula, whereas subjective ratings of similar stimuli are instead correlated with activation of the mid-insula, and more-so with the AIC.  A similar posterior-to-anterior-pattern of integration has been found in neuro-imaging studies of emotion.  The pattern, as Craig reminds us, is consistent with the processing gradient we already know about; we process the most complex of stimuli in our frontal cortex [2].

I found the functional imaging of side-to-side activation in the AIC with particular tasks and emotions really interesting.  Stimuli like pain, and more specifically the judgement of “how much” pain is being experienced [3], are found to activate the right AIC.  However, positive emotions and feelings light up more on the left; some examples include maternal and romantic love [4], smiling or seeing a pleased expression [5], and listening to pleasant music [6].

Two anatomically separate cortical regions and their co-activation can be confusing.  Craig suggested back in 2002 [1] that the AIC is a sensory limbic region and the ACC is a limbic motor area, with the two areas complementing each other and working together.  More recently supported [7] is Craig’s proposition that the AIC is probably the site of awareness of the body and the ACC is the likely site for the initiation of subsequent behaviour.  How do two ‘distant’ regions like the ACC and the AIC connect and communicate?  Craig proposes that von Economo neurons (VENs) are the answer.  Named after an early neuroanatomist, these large spindle-shaped neurons are a fascinating morphological characteristic of these two cortical areas in primates like us [8].

So… the AIC is activated with all subjective feelings but also in other contexts like decision-making, perception of time and of course sensorimotor awareness.  It is the only part of the brain that lights up on functional imaging in all these different contexts, and the common feature to all of these is the engagement of awareness in the subjects.  We can say then that the AIC ‘engenders human awareness’; the insula is the neural substrate for me knowing that ‘I am’…

About Flavia

Flavia Di PietroFlavia Di Pietro is a PhD student in the Moseley Group investigating the development of Complex Regional Pain Syndrome (CRPS) after wrist fracture. Flavia’s PhD focuses on the early detection of brain changes in CRPS using fMRI.  But get this – Flavia did Physiotherapy Honours degree at Notre Dame and completely cleaned up – Brian Edwards Memorial Award, Physio Research Foundation Award, Dean’s Award. Now, these things mean that she is not only ticking the academic boxes but all the other fluffy stuff too. No surprises that the NHMRC of Australia jumped to support her PhD.  So she has come over from Perth where she has been working as a physiotherapist.  All her achievements, however, pale in comparison to her celebrated status as the best Shoe Salesperson south of Milano, as evidenced by her taking out the 2006 and 2008 Diana Ferrari Golden Boot Award.  Clearly, she did not write this bio.

* One of the awards in Flavia’s bio is fictitious.

References

ResearchBlogging.org
[1] Craig, A. D. (2002) How do you feel? Interoception: the sense of the physiological condition of the body. Nature Rev. Neurosci. 3, 655-666.

[2] Koechlin E, & Jubault T (2006). Broca’s area and the hierarchical organization of human behavior. Neuron, 50 (6), 963-74 PMID: 16772176

[3] Baliki, M., Geha, P., & Apkarian, A. (2008). Parsing Pain Perception Between Nociceptive Representation and Magnitude Estimation Journal of Neurophysiology, 101 (2), 875-887 DOI: 10.1152/jn.91100.2008

[4] Bartels A, & Zeki S (2004). The neural correlates of maternal and romantic love. NeuroImage, 21 (3), 1155-66 PMID: 15006682

[5] Jabbi M, Swart M, & Keysers C (2007). Empathy for positive and negative emotions in the gustatory cortex. NeuroImage, 34 (4), 1744-53 PMID: 17175173

[6] Koelsch, S., Fritz, T., v. Cramon, D., Müller, K., & Friederici, A. (2006). Investigating emotion with music: An fMRI study Human Brain Mapping, 27 (3), 239-250 DOI: 10.1002/hbm.20180

[7] Heimer L, & Van Hoesen GW (2006). The limbic lobe and its output channels: implications for emotional functions and adaptive behavior. Neurosci Biobehav. Rev., 30 (2), 126-47 PMID: 16183121

[8] Nimchinsky, E. (1999). A neuronal morphologic type unique to humans and great apes Proceedings of the National Academy of Sciences, 96 (9), 5268-5273 DOI: 10.1073/pnas.96.9.5268

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