How do you feel — now? The anterior insula and human awareness

PersPectivescondition of the entire body in the posteriorinsular cortex 1 ; this includes numerousindividually mapped and distinct feelingsfrom the body. These neural constructs arethen re­represented in the mid­insula andagain in the AIC (on the left or right side orboth, depending on the source of the activity;BOX 3). The mid­insula integrates thesehomeostatic re­representations with activitythat is associated with emotionally salientenvironmental stimuli of many sensorymodalities, probably by way of input fromhigher­order sensory regions, the temporalpole and the amygdala. Recent functionalconnectivity analyses indicate that the midinsulais also modulated directly by theventral striatum (the nucleus accumbens) 79 ,which provides an important incentive,or hedonic, signal for the integration ofsalience. Thus, this posterior­to­anteriorprogression — which is consistent with thegeneral processing gradient for increasingcomplexity in the frontal cortex 22,65 and withthe enormous expansion of the anteriorinsula across hominoid primates — providesa substrate for the sequential integration ofhomeostatic conditions with the sensoryenvironment and with motivational, hedonicand social conditions represented in otherparts of the brain, and this substrate is constructedon the foundation provided by thefeelings from the body (FIG. 3a).I propose that the integration of salienceacross all of these factors culminatesin a unified final meta­representation of the‘global emotional moment’ near the junctionof the anterior insula and the frontal operculum.This processing stage is key, becauseit generates an image of ‘the material me’ (orthe sentient self) at one moment in time —‘now’. An anatomical repetition of this fundamentalunit, indexed by an endogenoustimebase, is all that is required to generate aset of repeated meta­representations of globalemotional moments that extends acrossa finite period of time, and this anatomicalstructure (a ‘meta­memory’) provides thebasis for the continuity of subjective emotionalawareness in a finite present 78 (FIG. 3b).The recent data emphasize that storage buffersfor individual global emotional momentsmust be present to enable comparisons ofpast, present and future feelings; this wouldinstantiate a reflexive ‘observer’, as notedabove. The anticipatory global emotionalmoments must be influenced by stored representationsof expectations that are basedon acquired internal models of one’s ownand others’ behaviour. A straightforward,although speculative, anatomical inferenceof this model is that meta­representations ofglobal emotional moments might be engenderedby clusters of VENs in the AIC, andthat these are interconnected with similarclusters of VENs in the ACC and probablyin the AIC and ACC on the opposite side(BOX 1), but the connections and functionsaPosterior insulabPrimaryinteroceptiverepresentationNormal time passagePastSubjective time passageHomeostaticmotor function(hypothalamusand amygdala)Environmentalconditions(entorhinal andtemporal poles)Presentof VENs still need to be identified. I believethat each successive stage of integration inthis model could have provided an evolutionaryadvantage, in that it would improveemotional communication between conspecifics— crucial for hominoid primates 80Hedonic conditions(nucleus accumbens,and orbitofrontalcortex)Anterior insulaMotivational, socialand cognitiveconditions (ACC,VMPFC and DLPFC)FutureWhen salient moments occur rapidly, thenumber of global emotional momentsincreases during that time and, as a consequence,subjective time dilatesFigure 3 | A proposed model of awareness. Cartoons illustrating features of the proposed structuralmodel of awareness. a | The posited integration of salient activity, progressing from the posterior insula(left) to the anterior insula (right). The primary interoceptive representations of feelings from the bodyNature Reviews | Neuroscienceprovide a somatotopic foundation that is anchored by the associated homeostatic effects on cardiorespiratoryfunction, as indicated by the focus of the colours in the chest. The integration successivelyincludes homeostatic, environmental, hedonic, motivational, social and cognitive activity to producea ‘global emotional moment’, which represents the sentient self at one moment of time. b | The topcartoon shows how a series of global emotional moments can produce a cinemascopic ‘image’ of thesentient self across time. The lower cartoon shows how the proposed model can produce a subjectivedilation of time during a period of high emotional salience, when global emotional moments are rapidly‘filled up’. ACC, anterior cingulate cortex; DLPFC, dorsolateral prefrontal cortex; vMPFC,ventromedial prefrontal cortex.NATuRE REVIEwS | NeuroscieNce VOLuME 10 | JANuARy 2009 | 67© 2009 Macmillan Publishers Limited. All rights reserved