Trends in Neurosciences
ReviewThe hidden island of addiction: the insula
Section snippets
Evidence for the role of the insula in addiction
Addiction to drugs of abuse is a major public health concern. By itself, cigarette smoking, the most common addictive behavior, is the largest preventable cause of morbidity and mortality in the developed world [1]. Drug addiction is a mental disorder characterized by the compulsive use of drugs that persists despite awareness of negative consequences [2]. Underlying addiction is a set of physiological and psychological processes, such as tolerance, withdrawal, learning, incentive motivation,
Anatomy and function of the insula: a historical perspective
The term ‘insula’ was coined by Johann Christian Reil who described an island of cortex (insula is Latin for island) in the depth of the cerebral mantle situated between the banks of the Sylvian fissure. The insula has been divided into various subregions based upon both anatomical connectivity and cytoarchitectonic features 13, 14, 15, 16, 17. The more posterior, granular regions of the insula, which receive inputs from the thalamus, in addition to parietal, occipital and temporal association
The psychology and neurobiology of addiction: a historical perspective
Various models have been applied to the phenomenon of impulsive and compulsive drug use, but most emphasize one of two possibilities. The first attributes drug motivation, especially with drugs that produce physical dependence such as opioids, to the need to alleviate the withdrawal-distress resultant from a previous history of drug use [75]. The other incentive possibility stresses drug-like rather than drug-withdrawal states as the most powerful instigator of drug use and that drug motivation
The role of interoception in addiction
Although the dopamine system clearly has an important role in addiction to drugs of abuse, drug use does more for the addicted individual than merely providing a means of releasing dopamine in the brain. Drug use involves a complex set of rituals imbued with emotional meaning (both positive and negative) for the addicted individual.
Nearly all drug-use rituals have highly salient and distinctive effects on the body that are likely to contribute to their emotional meaning. For example, snorting
Proposed role for the insula in addiction
Evidence points toward a crucial role for the insula in conscious drug urges and in translating interoceptive signals into conscious feelings and behavioral biases during decision making that involves uncertain risk and reward. Although nearly all drugs of abuse exert interoceptive effects that impart distinct subjective qualities to drug-use rituals, very little attention has been paid to the role of the insula in these effects. Thus, the question arises as to whether the insula has a role in
Future directions
Since our initial finding on the effects of insula lesions on smoking addiction, several authors have suggested that the interoceptive functions of the insula might be important for addiction 7, 12, 127, although they have only discussed these functions in general terms. Here, we propose a specific model in which interoceptive (i.e. bodily) effects of drug-use rituals are encoded by the insula and are integrated into explicit motivational processes that promote addiction, such as conscious
Acknowledgements
The research described in this article was supported by a grant from the National Institute on Drug Abuse (NIDA; www.nida.nih.gov) R01 DA023051.
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