Insular cortex
Encyclopedia
In each hemisphere of the mammal
ian brain
the insular cortex (often called insula, insulary cortex or insular lobe) is a portion of the cerebral cortex
folded deep within the lateral 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. In relation to these it is involved in psychopathology
.
The insula was first described by Johann Christian Reil
while describing cranial and spinal nerves and plexi. Henry Gray
in Gray's Anatomy
is responsible for it being known as the Island of Reil.
. 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. It is also involved in the control of blood pressure
, particularly during and after exercise. It is also activated when the brain perceives greater exertion
.
The insular cortex also is where the sensation of pain
is judged as to its degree. 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. Those with irritable bowel syndrome
have abnormal processing of visceral
pain in the insular cortex related to dysfunctional inhibition of pain within the brain.
Another perception of the right anterior insula is the degree of nonpainful warmth or nonpainful coldness of a skin sensation. Other internal sensations processed by the insula include stomach or gastric distension
. A full bladder
also activates the insular cortex.
The cerebral cortex processing vestibular
sensations extends into the insula with small lesions in the anterior insular cortex being able to cause loss of balance
and vertigo
.
Other noninteroceptive perceptions include passive listening to music, laughter and crying, empathy and compassion, and language.
and blood pressure
increase at the onset of exercise
. Research upon conversation links it to the capacity for long and complex spoken sentences. It is also involved in motor learning and has been identified as playing a role in the motor recovery from stroke.
both to smells and to the sight of contamination and mutilation — even when just imagining the experience. 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, emotional processing, empathy, and orgasms.
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 well as to motor cortices.
A study using magnetic resonance imaging
found that the right anterior insula was significantly thicker in people who meditate.
Another study using voxel-based morphometry and MRI on experienced Vipassana meditators was done to extend the findings of Lazar et al., which found increased grey matter concentrations in this and other areas of the brain in experienced meditators.
research suggests the insula is involved in two types of salience
. Interoceptive information processing that links interoception with emotional salience to generate a subjective representation of the body. This involves the anterior insular cortex with the pregenual anterior cingulate cortex (Brodmann area 33
) and the anterior and posterior mid-cingulate cortices. Second, a general salience system concerned with environmental monitoring, response selection, and skeletomotor body orientation that involves all of the insular cortex and the mid-cingulate cortex.
An alternative or perhaps complementary proposal is that right anterior insular regulates the interaction between the salience of the selective attention created to achieve a task (the dorsal attention system) and the salience of arousal
created to keep focused upon the relevant part of the environment (ventral attention system). This regulation of salience might be particularly important during challenging tasks where attention might fatigue
and so cause careless mistakes but if there is too much arousal it risks creating poor performance by turning into anxiety
.
. 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.
input along its length.
of the telencephalon
by some authorities. Other sources see the insula as a part of the temporal lobe
. It is also sometimes grouped with limbic structures deep in the brain into a limbic lobe
.
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. 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
.
, motor neuron disease, corticobasal degeneration
, frontotemporal dementia
and Alzheimer’s disease. It is associated with hypometabolism and atrophy of the left anterior insular cortex.
, 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 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
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.
A recent study in rats by Contreras et al. 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.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
the insular cortex (often called insula, insulary cortex or insular lobe) is a portion of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
folded deep within the lateral sulcus
Lateral sulcus
-External links:* * * http://www.uams.edu/radiology/education/residency/diagnostic/pdf/sylvian_cistern_RSNA2003.pdf...
between the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
and the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
. The cortical area overlying it towards the lateral surface of the brain is the operculum
Operculum (brain)
Operculum, derived from Latin, meaning "little lid", refers to the cerebral cortex on the outside surface of the brain bordering the lateral sulcus, and the roof and floor of the lateral sulcus. Neuroscience divides the operculum into orbital, frontal, parietal and temporal regions, after the...
(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
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
or the regulation of the body's homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
. These functions include perception, motor control, self-awareness, cognitive functioning, and interpersonal experience. In relation to these it is involved in psychopathology
Psychopathology
Psychopathology is the study of mental illness, mental distress, and abnormal/maladaptive behavior. The term is most commonly used within psychiatry where pathology refers to disease processes...
.
The insula was first described by Johann Christian Reil
Johann Christian Reil
Johann Christian Reil was a German physician, physiologist, anatomist and psychiatrist. He coined the term psychiatry or, in German, Psychiatrie in 1808....
while describing cranial and spinal nerves and plexi. Henry Gray
Henry Gray
Henry Gray was an English anatomist and surgeon most notable for publishing the book Gray's Anatomy. He was elected a Fellow of the Royal Society at the age of 25.-Biography:...
in Gray's Anatomy
Gray's Anatomy
Gray's Anatomy is an English-language human anatomy textbook originally written by Henry Gray. The book is widely regarded as an extremely influential work on the subject, and has continued to be revised and republished from its initial publication in 1858 to the present day...
is responsible for it being known as the Island of Reil.
Interoceptive awareness
The right anterior insula aids interoceptive awareness of body states, such as the ability to time one's own heart beatHeart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
. Moreover, greater right anterior insular gray matter
Gray Matter
"Gray Matter" is a short story by Stephen King, first published in the October 1973 issue of Cavalier magazine, and later collected in King's 1978 collection Night Shift. It is set in the same area as King's novel Dreamcatcher.-Setting:...
volume correlates with increased accuracy in this subjective sense of the inner body, and with negative emotional experience. It is also involved in the control of blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
, particularly during and after exercise. It is also activated when the brain perceives greater exertion
Exertion
Exertion is a concept describing the use of physical or perceived energy. It normally connotates a strenuous or costly effort related to physical, muscular, philosophical actions and work.-Physical:...
.
The insular cortex also is where the sensation of pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
is judged as to its degree. 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. Those with irritable bowel syndrome
Irritable bowel syndrome
Irritable bowel syndrome is a diagnosis of exclusion. It is a functional bowel disorder characterized by chronic abdominal pain, discomfort, bloating, and alteration of bowel habits in the absence of any detectable organic cause. In some cases, the symptoms are relieved by bowel movements...
have abnormal processing of visceral
Viscus
In anatomy, a viscus is an internal organ, and viscera is the plural form. The viscera, when removed from a butchered animal, are known collectively as offal...
pain in the insular cortex related to dysfunctional inhibition of pain within the brain.
Another perception of the right anterior insula is the degree of nonpainful warmth or nonpainful coldness of a skin sensation. Other internal sensations processed by the insula include stomach or gastric distension
Gastric distension
Gastric Distension is bloating of the stomach when air is pumped into it. This may be done when someone is performing cardiopulmonary resuscitation and blowing air into the mouth of someone who is not breathing spontaneously...
. A full bladder
Urinary bladder
The urinary bladder is the organ that collects urine excreted by the kidneys before disposal by urination. A hollow muscular, and distensible organ, the bladder sits on the pelvic floor...
also activates the insular cortex.
The cerebral cortex processing vestibular
Vestibular system
The vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
sensations extends into the insula with small lesions in the anterior insular cortex being able to cause loss of balance
Equilibrioception
Equilibrioception or sense of balance is one of the physiological senses. It helps prevent humans and animals from falling over when walking or standing still. Balance is the result of a number of body systems working together: the eyes , ears and the body's sense of where it is in space ideally...
and vertigo
Vertigo (medical)
Vertigo is a type of dizziness, where there is a feeling of motion when one is stationary. The symptoms are due to a dysfunction of the vestibular system in the inner ear...
.
Other noninteroceptive perceptions include passive listening to music, laughter and crying, empathy and compassion, and language.
Motor control
In motor control it contributes to hand and eye motor movement, swallowing, gastric motility, and speech articulation. It has been identified as a "central command” centre that ensures that heart rateHeart rate
Heart rate is the number of heartbeats per unit of time, typically expressed as beats per minute . Heart rate can vary as the body's need to absorb oxygen and excrete carbon dioxide changes, such as during exercise or sleep....
and blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
increase at the onset of exercise
Exercise physiology
Exercise physiology is the study of the acute responses and chronic adaptations to a wide-range of physical exercise conditions. In addition, many exercise physiologists study the effect of exercise on pathology, and the mechanisms by which exercise can reduce or reverse disease progression...
. Research upon conversation links it to the capacity for long and complex spoken sentences. It is also involved in motor learning and has been identified as playing a role in the motor recovery from stroke.
Homeostasis
In homeostasis it controls autonomic functions through the regulation of the sympathetic and parasympathetic systems. It has a role in regulating the immune system.Self
It has been identified as playing a role in the experience of bodily self-awareness, sense of agency and sense body ownership.Social emotions
The anterior insular processes a person's sense of disgustDisgust
Disgust is a type of aversion that involves withdrawing from a person or object with strong expressions of revulsion whether real or pretended. It is one of the basic emotions and is typically associated with things that are regarded as unclean, inedible, infectious, gory or otherwise offensive...
both to smells and to the sight of contamination and mutilation — even when just imagining the experience. This associates with a mirror neuron
Mirror neuron
A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behaviour of the other, as though the observer were itself acting. Such neurons have been directly observed in primate and other...
like link between external and internal experience.
In social experience it is involved in the processing of norm violations, emotional processing, empathy, and orgasms.
Emotions
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 DamasioAntonio Damasio
Antonio Damasio is David Dornsife Professor of Neuroscience at the University of Southern California, where he heads USC's Brain and Creativity Institute and Adjunct Professor at the Salk Institute. Prior to taking up his posts at USC, in 2005, Damasio was M.W...
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
William James
William James was a pioneering American psychologist and philosopher who was trained as a physician. He wrote influential books on the young science of psychology, educational psychology, psychology of religious experience and mysticism, and on the philosophy of pragmatism...
, 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
Embodied cognition
Philosophers, psychologists, cognitive scientists and artificial intelligence researchers who study embodied cognition and the embodied mind believe that the nature of the human mind is largely determined by the form of the human body. They argue that all aspects of cognition, such as ideas,...
.
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
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
experience and the experience of a number of basic emotions, including anger, fear, disgust
Disgust
Disgust is a type of aversion that involves withdrawing from a person or object with strong expressions of revulsion whether real or pretended. It is one of the basic emotions and is typically associated with things that are regarded as unclean, inedible, infectious, gory or otherwise offensive...
, 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
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, the ventral striatum
Ventral striatum
The ventral striatum is generally considered that part of the striatum that is connectionally associated with limbic structures, such as the amygdala, hippocampus, midline thalamus, and certain regions of the prefrontal cortex...
and the orbitofrontal cortex
Orbitofrontal cortex
The orbitofrontal cortex is a prefrontal cortex region in the frontal lobes in the brain which is involved in the cognitive processing of decision-making...
, as well as to motor cortices.
A study using magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
found that the right anterior insula was significantly thicker in people who meditate.
Another study using voxel-based morphometry and MRI on experienced Vipassana meditators was done to extend the findings of Lazar et al., which found increased grey matter concentrations in this and other areas of the brain in experienced meditators.
Salience
Functional imagingFunctional imaging
Functional imaging , is a method of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption....
research suggests the insula is involved in two types of salience
Salience (neuroscience)
The salience of an item – be it an object, a person, a pixel, etc – is the state or quality by which it stands out relative to its neighbours...
. Interoceptive information processing that links interoception with emotional salience to generate a subjective representation of the body. This involves the anterior insular cortex with the pregenual anterior cingulate cortex (Brodmann area 33
Brodmann area 33
Brodmann area 33, also known as pregenual area 33, is a subdivision of the cytoarchitecturally defined cingulate region of cerebral cortex. It is a narrow band located in the anterior cingulate gyrus adjacent to the supracallosal gyrus in the depth of the callosal sulcus...
) and the anterior and posterior mid-cingulate cortices. Second, a general salience system concerned with environmental monitoring, response selection, and skeletomotor body orientation that involves all of the insular cortex and the mid-cingulate cortex.
An alternative or perhaps complementary proposal is that right anterior insular regulates the interaction between the salience of the selective attention created to achieve a task (the dorsal attention system) and the salience of arousal
Arousal
Arousal is a physiological and psychological state of being awake or reactive to stimuli. It involves the activation of the reticular activating system in the brain stem, the autonomic nervous system and the endocrine system, leading to increased heart rate and blood pressure and a condition of...
created to keep focused upon the relevant part of the environment (ventral attention system). This regulation of salience might be particularly important during challenging tasks where attention might fatigue
Fatigue (safety)
Fatigue is a major safety concern in many fields, but especially in transportation, because fatigue can result in disastrous accidents. Fatigue is considered an internal precondition for unsafe acts because it negatively affects the human operator's internal state...
and so cause careless mistakes but if there is too much arousal it risks creating poor performance by turning into anxiety
Anxiety
Anxiety is a psychological and physiological state characterized by somatic, emotional, cognitive, and behavioral components. The root meaning of the word anxiety is 'to vex or trouble'; in either presence or absence of psychological stress, anxiety can create feelings of fear, worry, uneasiness,...
.
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 amygdalaAmygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
. 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.
Cytoarchitecture
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 thalamicThalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
input along its length.
Origins
The insular cortex is considered a separate lobeLobes of the brain
Brain lobes were originally a purely anatomical classification, but have been shown also to be related to different brain functions. The telencephalon , the largest portion of the human brain, is divided into lobes, but so is the cerebellum...
of the telencephalon
Telencephalon
The cerebrum or telencephalon, together with the diencephalon, constitutes the forebrain. The cerebrum is the most anterior region of the vertebrate central nervous system. Telencephalon refers to the embryonic structure, from which the mature cerebrum develops...
by some authorities. Other sources see the insula as a part of the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
. It is also sometimes grouped with limbic structures deep in the brain into a limbic lobe
Limbic lobe
The limbic lobe is an arc-shaped region of cortex on the medial surface of each cerebral hemisphere of the mammalian brain, consisting of parts of the frontal, parietal and temporal lobes...
.
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
John Allman
John Morgan Allman is a neuroscientist at the California Institute of Technology in Pasadena, California and a well recognized expert on primates, cognition and evolutionary neuroscience.-Life:He graduated from University of Chicago, with a PhD....
and his colleagues have shown that the anterior insular cortex contains a population of neurons, called spindle neurons. These neurons are also found in the anterior cingulate cortex
Anterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...
, 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
Empathy
Empathy is the capacity to recognize and, to some extent, share feelings that are being experienced by another sapient or semi-sapient being. Someone may need to have a certain amount of empathy before they are able to feel compassion. The English word was coined in 1909 by E.B...
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
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...
.
Progressive non-fluent aphasia
Progressive non-fluent aphasia is the deterioration of normal language function which causes individuals to lose the ability to communicate fluently while being still being able to comprehend single words and intact other non-linguistic cognition. It is found in a variety of degenerative neurological conditions including Pick's diseasePick's disease
Pick's disease, is a rare neurodegenerative disease that causes progressive destruction of nerve cells in the brain. Symptoms include loss of speech , and dementia. While some of the symptoms can initially be alleviated, the disease progresses and patients often die within two to ten years...
, motor neuron disease, corticobasal degeneration
Corticobasal degeneration
Corticobasal degeneration or Corticobasal Ganglionic Degeneration is a rare progressive neurodegenerative disease involving the cerebral cortex and the basal ganglia. It is characterized by marked disorders in movement and cognitive dysfunction...
, frontotemporal dementia
Frontotemporal dementia
Frontotemporal dementia is a clinical syndrome caused by degeneration of the frontal lobe of the brain and may extend back to the temporal lobe...
and Alzheimer’s disease. It is associated with hypometabolism and atrophy of the left anterior insular cortex.
Addiction
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, including cocaineCocaine
Cocaine is a crystalline tropane alkaloid that is obtained from the leaves of the coca plant. The name comes from "coca" in addition to the alkaloid suffix -ine, forming cocaine. It is a stimulant of the central nervous system, an appetite suppressant, and a topical anesthetic...
, alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
, opiates and nicotine
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
. 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
Dopamine
Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...
system which is central to current dopamine reward theories of addiction. Recent research has shown that cigarette
Cigarette
A cigarette is a small roll of finely cut tobacco leaves wrapped in a cylinder of thin paper for smoking. The cigarette is ignited at one end and allowed to smoulder; its smoke is inhaled from the other end, which is held in or to the mouth and in some cases a cigarette holder may be used as well...
smokers who suffer damage to the insular cortex, from a stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
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
Recall bias
In psychology, recall bias is a type of systematic bias which occurs when the way a survey respondent answers a question is affected not just by the correct answer, but also by the respondent's memory. This can affect the results of the survey. As a hypothetical example, suppose that a survey in...
could affect the results
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
Nicotine
Nicotine is an alkaloid found in the nightshade family of plants that constitutes approximately 0.6–3.0% of the dry weight of tobacco, with biosynthesis taking place in the roots and accumulation occurring in the leaves...
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.
A recent study in rats by Contreras et al. corroborates these findings by showing that reversible inactivation of the insula disrupts amphetamine conditioned place preference
Conditioned place preference
Conditioned place preference is a technique commonly used in animal studies to evaluate preferences for environmental stimuli that have been associated with a positive or negative reward...
, an animal model of cue-induced drug craving. In this study, insula inactivation also disrupted "malaise" responses to lithium chloride
Lithium chloride
Lithium chloride is a chemical compound with the formula LiCl. The salt is a typical ionic compound, although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlorides, such as extraordinary solubility in polar solvents and its hygroscopic...
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.
Other clinical conditions
The insular cortex has been suggested to have a role in anxiety disorders, and emotion dysregulation.External links
. Location and literature citations for the insula- NIF Search - Insula via the Neuroscience Information FrameworkNeuroscience Information FrameworkThe Neuroscience Information Framework is a repository of global neuroscience web resources, including experimental, clinical, and translational neuroscience databases, knowledge bases, atlases, and genetic/genomic resources.-Description:...