Insular cortex
From Wikipedia, the free encyclopedia
| Brain: Insular cortex | ||
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| The insula of the left side, exposed by removing the opercula. | ||
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| Coronal section of brain immediately in front of pons. (Insula labeled at upper right.) | ||
| Latin | lobus insularis | |
| Gray's | subject #189 825 | |
| NeuroNames | hier-93 | |
| Dorlands/Elsevier | i_09/12454066 | |
The insular cortex (also often referred to as just the 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 Latin name for the insular cortex is lobus insularis.
The insular cortex is also known by the name Island of Reil, named after Johann Christian Reil.
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[edit] Contrasting anterior and posterior architecture
It 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.
[edit] Role in the limbic system
The insular cortex, in particular its most anterior portion, is considered a limbic-related cortex. Overall, the insula is believed to process convergent information to produce an emotionally relevant context for sensory experience, such as disgust and feelings of unease. 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. The insula is well situated for the integration of information relating to the affective and reactive components of pain as part of the circuitry related to fear avoidance. The insula is related to a number of other limbic-related structures, such as the amygdala, the ventral striatum and the orbitofrontal cortex. It 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.
[edit] Phylogenetic considerations
As a component of the limbic system, 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). However, 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.
