Wiki: Insular Cortex

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In each hemisphere of the mammalian brain the insular cortex (often called insula, insulary cortex or insular lobe) is a portion of the cerebral cortex folded deep within thelateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum (meaning “lid”). The opercula are formed from parts of the enclosing frontal, temporal and parietal lobes. It is believed to be involved in consciousness.

The insular cortex is divided into two parts: the larger anterior insula and the smaller posterior insula in which more than a dozen field areas have been identified.

The insulae play a role in diverse functions usually linked to emotion or the regulation of the body’s homeostasis. These functions include perception, motor control, self-awareness, cognitive functioning, and interpersonal experience. Related to these it is involved in psychopathology.

The insula was first described by Johann Christian Reil while describing cranial and spinal nerves and plexi.^[1] Henry Gray in Gray’s Anatomy is responsible for it being known as the Island of Reil.^[1]

Functions

Interoceptive awareness

The right anterior insula aids interoceptive awareness of body states, such as the ability to time one’s own heart beat. Moreover, greater right anterior insular gray matter volume correlates with increased accuracy in this subjective sense of the inner body, and with negative emotional experience.^[2] It is also involved in the control of blood pressure,^[3] particularly during and after exercise.^[3] It is also activated when the brain perceives greater exertion.^[4][5]

The insular cortex also is where the sensation of pain is judged as to its degree.^[6] Further, the insula is where a person imagines pain when looking at images of painful events while thinking about them happening to one’s own body.^[7] Those with irritable bowel syndrome have abnormal processing of visceral pain in the insular cortex related to dysfunctional inhibition of pain within the brain.^[8]

Another perception of the right anterior insula is the degree of nonpainful warmth^[9] or nonpainful coldness^[10] of a skin sensation. Other internal sensations processed by the insula include stomach or gastric distension.^[11][12] A full bladder also activates the insular cortex.^[13]

The cerebral cortex processing vestibular sensations extends into the insula^[14] with small lesions in the anterior insular cortex being able to cause loss of balance and vertigo.^[15]

Other noninteroceptive perceptions includes passive listening to music,^[16] laughter and crying,^[17], empathy and compassion,^[18] and language ^[19]

Motor control

In motor control it contributes to hand and eye motor movement,^[20][21] swallowing,^[22] gastric motility,^[23] and speech articulation.^[24][25] It has been identified as a “central command” centre that ensures that heart rateand blood pressure increase at the onset of exercise.^[26] Research upon conversation links it to the capacity for long and complex spoken sentences.^[27] It is also involved in motor learning^[28] and has been identified as playing a role in the motor recovery from stroke.^[29]

Homeostasis

In homeostasis, it controls autonomic functions through the regulation of the sympathetic and parasympathetic systems.^[30][31] It has a role in regulating the immune system.^[32][33][34]

Self

It has been identified as playing a role in the experience of bodily self-awareness,^[35][36] sense of agency^[37] and sense body ownership.^[38]

Social emotions

The anterior insular processes a person’s sense of disgust both to smells^[39] and to the sight of contamination and mutilation^[40] — even when just imagining the experience.^[41] This associates with a mirror neuron like link between external and internal experience.

In social experience it is involved in the processing of norm violations,^[42] emotional processing,^[43] empathy,^[44] and orgasms.^[45

Neuroanatomy

Connections

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.

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