Insular cortex

Infobox Brain
Name = Insular cortex
Latin = lobus insularis
boxwidth = 19em
GraySubject = 189
GrayPage = 825

---

Width = 250
Caption = The insula of the left side, exposed by removing the opercula.


Caption2 = Coronal section of brain immediately in front of pons. (Insula labeled at upper right.)
IsPartOf =
Components =
Artery = Middle cerebral
Vein =
Acronym =
BrainInfoType = hier
BrainInfoNumber = 93
MeshName =
MeshNumber =
DorlandsPre = i_09
DorlandsSuf = 12454066The insular cortex (abbrev. insula) is a structure of the human brain. It lies deep to the brain's lateral surface, within the lateral sulcus which separates the temporal lobe and inferior parietal cortex. These overlying cortical areas are known as opercula (meaning "lids"), and parts of the frontal, temporal and parietal lobes form opercula over the insula.

The insular cortex is also known by the name Island of Reil, named after Johann Christian Reil.Its Latin name is "lobus insularis".

The insular cortex is considered a separate lobe of the telencephalon by some authorities. [ [http://encarta.msn.com/encyclopedia_761555359/Brain.html Brain] , MSN Encarta.] Other sources see the insula as a part of the temporal lobe. [Kolb & Whishaw: "Fundamentals of Human Neuropsychology", 2003] It is also sometimes grouped with limbic structures deep in the brain into a limbic lobe.Fact|date=March 2008

Contrasting anterior and posterior architecture

The insular cortex has regions of variable cell structure or cytoarchitecture, changing from granular in the posterior portion to agranular in the anterior portion. The insula also receives differential cortical and thalamic input along its length. The anterior insula receives a direct projection from the basal part of the ventral medial nucleus (VMb) of the thalamus and a particularly large input from the central nucleus of the amygdala. Additionally, the anterior insula itself projects to the amygdala. The posterior insula connects reciprocally with the secondary primary sensory cortex (S2) and receives input from spinothalamically activated ventral posterior inferior (VPI) thalamic nuclei. More recent work by Bud Craig and his colleagues has shown that this region receives inputs from the ventromedial nucleus (posterior part) of the thalamus that are highly specialized to convey emotional/homeostatic information such as pain, temperature, itch, local oxygen status and sensual touch. Williamson and colleagues have also reported the posterior human insula is involved in the perception of effort during exercise.

Role in emotions and feelings (relationship to the "limbic system")

The insular cortex, in particular its most anterior portion, is considered a limbic-related cortex. The insula has increasingly become the focus of attention for its role in body representation and subjective emotional experience. In particular, Antonio Damasio has proposed that this region plays a role in mapping visceral states that are associated with emotional experience, giving rise to conscious feelings. This is in essence a neurobiological formulation of the ideas of William James, who first proposed that subjective emotional experience (i.e. feelings) arise from our brain's interpretation of bodily states that are elicited by emotional events. This is an example of embodied cognition.

Functionally speaking, the insula is believed to process convergent information to produce an "emotionally relevant context for sensory experience". More specifically, the anterior insula is related more to "olfactory, gustatory, vicero-autonomic, and limbic function", while the posterior insula is related more to "auditory-somesthetic-skeletomotor" function. Functional imaging experiments have revealed that the insula has an important role in pain experience and the experience of a number of basic emotions, including anger, fear, disgust, happiness and sadness.

Functional imaging studies have also implicated the insula in conscious desires, such as food craving and drug craving. What is common to all of these emotional states is that they each change the body in some way and are associated with highly salient subjective qualities. The insula is well situated for the integration of information relating to bodily states into higher-order cognitive and emotional processes. The insula receives information from "homeostatic afferent" sensory pathways via the thalamus and sends output to a number of other limbic-related structures, such as the amygdala, the ventral striatum and the orbitofrontal cortex.

A single study using magnetic resonance imaging has found that the right anterior insula was significantly thicker in people who meditate. [Cite journal
title = Meditation experience is associated with increased cortical thickness
author = Sara W. Lazar, Catherine E. Kerr, Rachel H. Wasserman, Jeremy R. Gray, Douglas N. Greve, Michael T. Treadway, Metta McGarvey, Brian T. Quinn, Jeffery A. Dusek, Herbert Benson, Scott L. Rauch, Christopher I. Moore, and Bruce Fischl
journal = NeuroReport
year = 2005
month = November
volume = 16
issue = 17
pages = 1893–1897
url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1361002
doi = 10.1097/01.wnr.0000186598.66243.19
pmid = 16272874]

Role in addiction

"The insula also reads body states like hunger and craving and helps push people into reaching for the next sandwich, cigarette or line of cocaine." [ cite news
last= Blakeslee
first= Sandra
url= http://www.nytimes.com/2007/02/06/health/psychology/06brain.html
title= A Small Part of the Brain, and Its Profound Effects
publisher= The New York Times
date= February 6, 2007
accessdate= ] A number of functional brain imaging studies have shown that the insular cortex is activated when drug abusers are exposed to environmental cues that trigger cravings. This has been shown for a variety of drugs of abuse, including cocaine, alcohol, opiates and nicotine. Despite these findings, the insula has been ignored within the drug addiciton literature, perhaps because it is not known to be a direct target of the mesotelencephalic dopamine system which is central to current dopamine reward theories of addiction. Recent research [Cite journal
author = Nasir H. Naqvi, David Rudrauf, Hanna Damasio, Antoine Bechara.
title = Damage to the Insula Disrupts Addiction to Cigarette Smoking
journal = Science
year = 2007
month = January
volume = 315
issue = 5811
pages = 531–534
doi = 10.1126/science.1135926
url = http://www.sciencemag.org/cgi/content/abstract/315/5811/531
format = abstract
pmid = 17255515] has shown that cigarette smokers who suffer damage to the insular cortex, from a stroke for instance, have their addiction to cigarettes practically eliminated. However, the study was conducted on average eight years after the strokes, and the author admits recall bias could affect the results [10.1126/science.317.5836.318c]

These individuals were found to be up to 136 times more likely to undergo a disruption of smoking addiction than smokers with damage in other areas. Disruption of addiction was evidenced by self-reported behavior changes such as quitting smoking less than one day after the brain injury, quitting smoking with great ease, not smoking again after quitting, and having no urge to resume smoking since quitting. This suggests a significant role for the insular cortex in the neurological mechanisms underlying addiction to nicotine and other drugs, and would make this area of the brain a possible target for novel anti-addiction medication. In addition, this finding suggests that functions mediated by the insula, especially conscious feelings, may be particularly important for maintaining drug addiction, although this view is not represented in any modern research or reviews of the subject. [Cite journal
doi = 10.1176/appi.ajp.162.8.1414
volume = 162
issue = 8
pages = 1414–1422
last = Hyman
first = Steven E.
title = Addiction: A Disease of Learning and Memory
journal = Am J Psychiatry
accessdate = 2008-03-04
date = 2005-08-01
url = http://ajp.psychiatryonline.org/cgi/content/abstract/162/8/1414
format = abstract
pmid = 16055762

]

A recent study in rats by Contreras et al. [Cite journal
author = Marco Contreras, Francisco Ceric, Fernando Torrealba
title = Inactivation of the Interoceptive Insula Disrupts Drug Craving and Malaise Induced by Lithium
journal = Science
year = 2007
month = January
volume = 318
issue = 5850
pages = 655–658
doi = 10.1126/science.1145590
url = http://www.sciencemag.org/cgi/content/abstract/318/5850/655
format = abstract
pmid = 17962567] corroborates these findings by showing that reversible inactivation of the insula disrupts amphetamine conditioned place preference, an animal model of cue-induced drug craving. In this study, insula inactivation also disrupted "malaise" responses to lithium chloride injection, suggesting that the representation of negative interoceptive states by the insula plays a role in addiction. However, in this same study, the conditioned place preference took place immediately after the injection of amphetamine, suggesting that it was the immediate, pleasurable interoceptive effects of amphetamine administration, rather than the delayed, aversive effects of amphetamine withdrawal that are represented within the insula.

A model proposed by Naqvi et al. (see above) is that the insula stores a representation of the pleasurable interoceptive effects of drug use (e.g. the airway sensory effects of nicotine, the cardiovascular effects of amphetamine), and that this representation is activated by exposure to cues that have previously been associated with drug use. A number of functional imaging studies have shown the insula to be activated during the administration of drugs of abuse. Several functional imaging studies have also shown that the insula is activated when drug users are exposed to drug cues, and that this activity is correlated with subjective urges. In the cue-exposure studies, insula activity is elicited when there is no actual change in the level of drug in the body. Therefore, rather than merely representing the interoceptive effects of drug use as it occurs, the insula may play a role in memory for the pleasurable interoceptive effects of past drug use, anticipation of these effects in the future, or both. Such a representation may give rise to conscious urges that feel as if they arise from within the body. This may make addicts feel as if their bodies need to use a drug, and may result in persons with lesions in the insula reporting that their bodies have forgotten the urge to use, according to this study.

Phylogenetic considerations

As a paralimbic cortex, the insular cortex is considered to be a relatively old structure. It plays a role in a variety of highly conserved functions that are related to basic survival needs, such as taste, visceral sensation and autonomic control (so-called homeostatic functions). There is evidence that in addition to its more conserved functions, the insula may play a role in certain "higher" functions that operate only in humans and other great apes. John Allman and his colleagues have shown that the anterior insular cortex contains a population of neurons, called spindle neurons, that are specific to great apes. These neurons are also found in the anterior cingulate cortex, which is another region that has reached a high level of specialization in great apes. Spindle neurons are found at a higher density in the right insular cortex. It has been speculated that these neurons are involved in cognitive-emotional processes that are specific to great apes, such as empathy and self-aware emotional feelings. This is supported by functional imaging results showing that the structure and function of the right anterior insula are correlated with the ability to feel one's own heartbeat, or to empathize with the pain of others. It is thought that these functions are not distinct from the "lower" functions of the insula, but rather arise as a consequence of the role of the insula in conveying homeostatic information to consciousness.

=Additional

References

External links

* Cite journal
title = The Insula: Anatomic Study and MR Imaging Display at 1.5 T
author = Thomas P. Naidicha, et al.
journal = American Journal of Neuroradiology
volume = 25
pages = 222–232
month = February
year = 2004
url = http://www.ajnr.org/cgi/content/full/25/2/222
pmid = 14970021

See also

* List of regions in the human brain

External links

* [http://hendrix.ei.dtu.dk/services/jerne/brede/WOROI_67.html WOROI: 67 - Insula] . Location and literature citations for the insula
*
*
*