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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)
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The (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 , named after
Johann Christian Reil .
Its Latin name is ''.
The insular cortex is considered a separate .
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.
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 .
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 .
