The insular cortex (also insula and insular lobe) is a portion of the
cerebral cortex
The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting of ...
folded deep within the
lateral sulcus
In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates the ...
(the fissure separating the
temporal lobe
The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe ...
from the
parietal and
frontal lobe
The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove betwe ...
s) within each
hemisphere
Hemisphere refers to:
* A half of a sphere
As half of the Earth
* A hemisphere of Earth
** Northern Hemisphere
** Southern Hemisphere
** Eastern Hemisphere
** Western Hemisphere
** Land and water hemispheres
* A half of the (geocentric) celes ...
of the
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
ian
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
.
The insulae are believed to be involved in
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
and play a role in diverse functions usually linked to
emotion
Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...
or the regulation of the body's
homeostasis
In biology, homeostasis (British English, British also homoeostasis) Help:IPA/English, (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physics, physical, and chemistry, chemical conditions maintained by organism, living systems. Thi ...
. These functions include
compassion
Compassion motivates people to go out of their way to relieve the physical, mental or emotional pains of others and themselves. Compassion is often regarded as being sensitive to the emotional aspects of the suffering of others. When based on n ...
,
empathy
Empathy is the capacity to understand or feel what another person is experiencing from within their frame of reference, that is, the capacity to place oneself in another's position. Definitions of empathy encompass a broad range of social, co ...
,
taste
The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
,
perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
,
motor control
Motor control is the regulation of movement in organisms that possess a nervous system. Motor control includes reflexes as well as directed movement.
To control movement, the nervous system must integrate multimodal sensory information (both f ...
,
self-awareness
In philosophy of self, self-awareness is the experience of one's own personality or individuality. It is not to be confused with consciousness in the sense of qualia. While consciousness is being aware of one's environment and body and lifesty ...
,
cognitive function
Cognitive skills, also called cognitive functions, cognitive abilities or cognitive capacities, are brain-based skills which are needed in acquisition of knowledge, manipulation of information and reasoning. They have more to do with the mechanisms ...
ing,
interpersonal experience, and awareness of
homeostatic emotion
Homeostatic feeling (or homeostatic affect, or homeostatic emotion, or primordial emotion) is a class of feelings (e.g., thirst, pain, fatigue) evoked by an internal body state. Some homeostatic feelings drive specific behavior (drinking, with ...
s such as hunger, pain and fatigue. In relation to these, it is involved in
psychopathology.
The insular cortex is divided into two parts: the anterior insula and the posterior insula in which more than a dozen field areas have been identified. The cortical area overlying the insula toward 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.
Structure
Connections
The anterior part of the insula is subdivided by shallow sulci into three or four short gyri.
The anterior insula receives a direct projection from the basal part of the
ventral medial nucleus of the thalamus and a particularly large input from the
central nucleus of the amygdala. In addition, the anterior insula itself projects to the
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
.
One study on rhesus monkeys revealed widespread reciprocal connections between the insular cortex and almost all subnuclei of the amygdaloid complex. The posterior insula projects predominantly to the dorsal aspect of the lateral and to the central amygdaloid nuclei. In contrast, the anterior insula projects to the anterior amygdaloid area as well as the medial, the cortical, the accessory basal magnocellular, the medial basal, and the lateral amygdaloid nuclei.
The posterior part of the insula is formed by a long gyrus.
The posterior insula connects reciprocally with the
secondary somatosensory cortex
The human secondary somatosensory cortex (S2, SII) is a region of cortex in the parietal operculum on the ceiling of the lateral sulcus.
Region S2 was first described by Adrian in 1940, who found that feeling in cats' feet was not only represe ...
and receives input from
spinothalamically activated
ventral posterior inferior thalamic nuclei. It has also been shown that this region receives inputs from the ventromedial nucleus (posterior part) of the thalamus that are highly specialized to convey homeostatic information such as pain, temperature, itch, local oxygen status, and sensual touch.
A human neuroimaging study using
diffusion tensor imaging revealed that the anterior insula is interconnected to regions in the temporal and occipital lobe, opercular and orbitofrontal cortex, triangular and opercular parts of the inferior frontal gyrus. The same study revealed differences in the anatomical connection patterns between the left and right hemisphere.
The 'circular sulcus of insula' (or sulcus of Reil
) is a semi-circular
sulcus or ''fissure''
that separates the insula from the neighboring gyri of the
operculum in the front, above, and
behind.
Cytoarchitecture
The insular cortex has regions of variable cell structure or
cytoarchitecture
Cytoarchitecture ( Greek '' κύτος''= "cell" + '' ἀρχιτεκτονική''= "architecture"), also known as cytoarchitectonics, is the study of the cellular composition of the central nervous system's tissues under the microscope. Cytoarc ...
, changing from
granular
Granularity (also called graininess), the condition of existing in granules or grains, refers to the extent to which a material or system is composed of distinguishable pieces. It can either refer to the extent to which a larger entity is subd ...
in the
posterior portion to agranular in the
anterior portion. The insula also receives differential
cortical and
thalamic input along its length. The anterior insular cortex contains a population of
spindle neurons
Von Economo neurons (VENs), also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that ''transmits ...
(also called ''von Economo neurons''), identified as characterising a distinctive subregion as the agranular frontal insula.
Development
The insular cortex is considered a separate
lobe
Lobe may refer to:
People with the name
* Lobe (surname)
Science and healthcare
* Lobe (anatomy)
* Lobe, a large-scale structure of a radio galaxy
* Glacial lobe, a lobe-shaped glacier
* Lobation, a characteristic of the nucleus of certain biolo ...
of the
telencephalon
The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
by some authorities. Other sources see the insula as a part of the
temporal lobe
The temporal lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The temporal lobe is located beneath the lateral fissure on both cerebral hemispheres of the mammalian brain.
The temporal lobe ...
. It is also sometimes grouped with limbic structures deep in the brain into a
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. The term is ambiguous, with some authors including the p ...
. As a paralimbic cortex, the insular cortex is considered to be a relatively old structure.
Function
Multimodal sensory processing, sensory binding
Functional imaging studies show activation of the insula during audio-visual integration tasks.
Taste
The anterior insula is part of the primary
gustatory cortex The primary gustatory cortex is a brain structure responsible for the perception of taste. It consists of two substructures: the anterior insula on the insular lobe and the frontal operculum on the inferior frontal gyrus of the frontal lobe. ...
.
Interoceptive awareness
There is evidence that, in addition to its base functions, the insula may play a role in certain higher-level functions that operate only in humans and other
great apes
The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); ''Gorilla'' (the ...
. The spindle neurons found at a higher density in the right frontal insular cortex are also found in the
anterior cingulate cortex
In the human brain, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33.
It is involved ...
, which is another region that has reached a high level of specialization in great apes. It has been speculated that these neurons are involved in
cognitive
Cognition refers to "the mental action or process of acquiring knowledge and understanding through thought, experience, and the senses". It encompasses all aspects of intellectual functions and processes such as: perception, attention, thought, ...
-
emotion
Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...
al processes that are specific to primates including great apes, such as
empathy
Empathy is the capacity to understand or feel what another person is experiencing from within their frame of reference, that is, the capacity to place oneself in another's position. Definitions of empathy encompass a broad range of social, co ...
and
metacognitive emotional feelings. This is supported by functional imaging results showing that the structure and function of the right frontal insula is 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-level functions of the insula but rather arise as a consequence of the role of the insula in conveying homeostatic information to
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
. The right anterior insula is engaged in
interoceptive awareness of homeostatic emotions such as thirst, pain and fatigue, and the ability to time one's own
heartbeat. Moreover, greater right anterior insular
gray matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distingui ...
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 (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
,
in particular during and after exercise,
and its activity varies with the amount of effort a person believes he/she is exerting.
The insular cortex also is where the sensation of
pain
Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
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 their happening to one's own body. Those with
irritable bowel syndrome
Irritable bowel syndrome (IBS) is a "disorder of gut-brain interaction" characterized by a group of symptoms that commonly include abdominal pain and or abdominal bloating and changes in the consistency of bowel movements. These symptoms may ...
have abnormal processing of
visceral
In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...
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
abdominal distension
Abdominal distension occurs when substances, such as air (gas) or fluid, accumulate in the abdomen causing its expansion. It is typically a symptom of an underlying disease or dysfunction in the body, rather than an illness in its own right. Pe ...
. A full
bladder
The urinary bladder, or simply bladder, is a hollow organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a distensible organ that sits on the pelvic floor. Urine enters ...
also activates the insular cortex.
One brain imaging study suggests that the unpleasantness of subjectively perceived
dyspnea
Shortness of breath (SOB), also medically known as dyspnea (in AmE) or dyspnoea (in BrE), is an uncomfortable feeling of not being able to breathing, breathe well enough. The American Thoracic Society defines it as "a subjective experience of brea ...
is processed in the right human anterior insula and
amygdala
The amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
.
The cerebral cortex processing
vestibular
The Vestibular (from pt, vestíbulo, "entrance hall") is a competitive examination and is the primary and widespread entrance system used by Brazilian universities to select the students admitted.
The Vestibular usually takes place from Nove ...
sensations extends into the insula, with small lesions in the anterior insular cortex being able to cause loss of
balance
Balance or balancing may refer to:
Common meanings
* Balance (ability) in biomechanics
* Balance (accounting)
* Balance or weighing scale
* Balance as in equality or equilibrium
Arts and entertainment Film
* ''Balance'' (1983 film), a Bulgaria ...
and
vertigo
Vertigo is a condition where a person has the sensation of movement or of surrounding objects moving when they are not. Often it feels like a spinning or swaying movement. This may be associated with nausea, vomiting, sweating, or difficulties w ...
.
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 rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
and
blood pressure
Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "blood pressure" r ...
increase at the onset of
exercise
Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness.
It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic ...
. 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
It plays a role in a variety of homeostatic functions related to basic survival needs, such as taste, visceral sensation, and autonomic control. The insula controls autonomic functions through the regulation of the sympathetic and parasympathetic systems.
It has a role in regulating the immune system.
Self
The insula has been identified as playing a role in the experience of bodily self-awareness, sense of agency, and sense of body ownership.
Social emotions
The anterior insula processes a person's sense of
disgust
Disgust (Middle French: ''desgouster'', from Latin ''gustus'', "taste") is an emotional response of rejection or revulsion to something potentially contagious or something considered offensive, distasteful, or unpleasant. In ''The Expression o ...
both to smells
and to the sight of contamination and mutilation — even when just imagining the experience.
This associates with a
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 behavior of the other, as though the observer were itself acting. Such neurons ha ...
-like link between external and internal experiences.
In social experience, it is involved in the processing of norm violations, emotional processing, empathy, and orgasms.
The insula is active during social decision making. Tiziana Quarto et al. measured
emotional intelligence
Emotional intelligence (EI) is most often defined as the ability to perceive, use, understand, manage, and handle emotions. People with high emotional intelligence can emotion recognition, recognize their own emotions and those of others, use em ...
(EI) (the ability to identify, regulate, and process emotions of themselves and of others) of sixty-three healthy subjects. Using
fMRI
Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...
EI was measured in correlation with left insular activity. The subjects were shown various pictures of
facial expression
A facial expression is one or more motions or positions of the muscles beneath the skin of the face. According to one set of controversial theories, these movements convey the emotional state of an individual to observers. Facial expressions are a ...
s and tasked with deciding to approach or avoid the person in the picture. The results of the social decision task yielded that individuals with high EI scores had left insular activation when processing fearful faces. Individuals with low EI scores had left insular activation when processing angry faces.
Emotions
The insular cortex, in particular its most anterior portion, is considered a
limbic
The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...
-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
Antonio Damasio ( pt, António Damásio) is a Portuguese-American neuroscientist. He is currently the David Dornsife Chair in Neuroscience, as well as Professor of Psychology, Philosophy, and Neurology, at the University of Southern California, ...
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 (January 11, 1842 – August 26, 1910) was an American philosopher, historian, and psychologist, and the first educator to offer a psychology course in the United States.
James is considered to be a leading thinker of the lat ...
, 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 is the theory that many features of cognition, whether human or otherwise, are shaped by aspects of an organism's entire body. Sensory and motor systems are seen as fundamentally integrated with cognitive processing. The cognit ...
.
In terms of function, the insula is believed to process convergent information to produce an ''emotionally relevant context for sensory experience''. To be specific, the anterior insula is related more to ''olfactory, gustatory, viscero-autonomic, and limbic function'', whereas 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 is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, ...
experience and the experience of a number of basic
emotions
Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...
, including
anger
Anger, also known as wrath or rage, is an intense emotional state involving a strong uncomfortable and non-cooperative response to a perceived provocation, hurt or threat.
A person experiencing anger will often experience physical effects, su ...
,
fear
Fear is an intensely unpleasant emotion in response to perceiving or recognizing a danger or threat. Fear causes physiological changes that may produce behavioral reactions such as mounting an aggressive response or fleeing the threat. Fear ...
,
disgust
Disgust (Middle French: ''desgouster'', from Latin ''gustus'', "taste") is an emotional response of rejection or revulsion to something potentially contagious or something considered offensive, distasteful, or unpleasant. In ''The Expression o ...
,
happiness
Happiness, in the context of Mental health, mental or emotional states, is positive or Pleasure, pleasant emotions ranging from contentment to intense joy. Other forms include life satisfaction, well-being, subjective well-being, flourishin ...
, and
sadness
Sadness is an emotional pain associated with, or characterized by, feelings of disadvantage, loss, despair, grief, helplessness, disappointment and sorrow. An individual experiencing sadness may become quiet or lethargic, and withdraw thems ...
.
The anterior insular cortex (AIC) is believed to be responsible for emotional feelings, including maternal and romantic love, anger, fear, sadness, happiness, sexual arousal, disgust, aversion, unfairness, inequity, indignation, uncertainty, disbelief, social exclusion, trust, empathy, sculptural beauty, a ‘state of union with God’, and hallucinogenic states.
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 amygdala (; plural: amygdalae or amygdalas; also '; Latin from Greek, , ', 'almond', 'tonsil') is one of two almond-shaped clusters of nuclei located deep and medially within the temporal lobes of the brain's cerebrum in complex verteb ...
, the
ventral striatum
The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutam ...
, and the
orbitofrontal cortex
The orbitofrontal cortex (OFC) is a prefrontal cortex region in the frontal lobes of the brain which is involved in the cognitive process of decision-making. In non-human primates it consists of the association cortex areas Brodmann area 11, 12 ...
, as well as to
motor cortices.
A study using
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
found that the right anterior insula is significantly thicker in people that
meditate
Meditation is a practice in which an individual uses a technique – such as mindfulness, or focusing the mind on a particular object, thought, or activity – to train attention and awareness, and achieve a mentally clear and emotionally calm ...
.
Other research into
brain activity and meditation has shown an increase in grey matter in areas of the brain including the insular cortex.
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.
The strongest evidence against a causative role for the insula cortex in emotion comes from Damasio et al. (2012) which showed that a patient who suffered bilateral lesions of the insula cortex expressed the full complement of human emotions, and was fully capable of emotional learning.
Salience
Functional neuroimaging
Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions. It is primarily used a ...
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, first, the anterior insular cortex with the
pregenual anterior cingulate cortex (
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 d ...
) and the anterior and
posterior mid-cingulate cortices, and, second, a general
salience network
The salience network (SN), also known anatomically as the midcingulo-insular network (M-CIN), is a large scale brain network of the human brain that is primarily composed of the anterior insula (AI) and dorsal anterior cingulate cortex (dACC). ...
concerned with environmental monitoring, response selection, and skeletomotor body orientation that involves all of the insular cortex and the mid-cingulate cortex. A related idea is that the anterior insula, as part of the salience network, interacts with the mid-posterior insula to combine salient stimuli with autonomic information, leading to a high state of physiological awareness of salient stimuli.
An alternative or perhaps complementary proposal is that the right anterior insular regulates the interaction between the salience of the
selective attention
Attentional control, colloquially referred to as concentration, refers to an individual's capacity to choose what they pay attention to and what they ignore. It is also known as endogenous attention or executive attention. In lay terms, attenti ...
created to achieve a task (the dorsal attention system) and the salience of
arousal
Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, th ...
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
Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...
.
Auditory perception
Recent research indicates that the insular cortex is involved in
auditory perception. Responses to sound stimuli were obtained using
intracranial EEG recordings acquired from patients with epilepsy. The posterior part of the insula showed auditory responses that resemble those observed in
Heschl’s gyrus, whereas the anterior part responded to the emotional contents of the auditory stimuli.
Direct recordings from the posterior part of the insula showed responses to unexpected sounds within regular auditory streams, a process known as
auditory deviance detection. Researchers observed a
mismatch negativity (MMN) potential, a well known
event related potential
An event-related potential (ERP) is the measured brain response that is the direct result of a specific sensory, cognitive, or motor event. More formally, it is any stereotyped electrophysiological response to a stimulus. The study of the brai ...
, as well as the high frequency activity signals originating from local neurons.
Simple auditory illusions and hallucinations were elicited by electrical functional mapping.
Clinical significance
Progressive expressive aphasia
Progressive
expressive aphasia
Expressive aphasia, also known as Broca's aphasia, is a type of aphasia characterized by partial loss of the ability to produce language ( spoken, manual, or written), although comprehension generally remains intact. A person with expressive apha ...
is the deterioration of normal
language function that causes individuals to lose the ability to communicate fluently while 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 disease
Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as ...
,
motor neuron disease
Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...
,
corticobasal degeneration
Corticobasal degeneration (CBD) is a rare neurodegenerative disease involving the cerebral cortex and the basal ganglia. CBD symptoms typically begin in people from 50 to 70 years of age, and the average disease duration is six years. It is chara ...
,
frontotemporal dementia
Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as ...
, and
Alzheimer's disease
Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
. 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 users are exposed to environmental cues that trigger cravings. This has been shown for a variety of drugs, including
cocaine
Cocaine (from , from , ultimately from Quechuan languages, Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly recreational drug use, used recreationally for its euphoria, euphoric effects. It is primarily obtained from t ...
,
alcohol,
opiates
An opiate, in classical pharmacology, is a substance derived from opium. In more modern usage, the term ''opioid'' is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain (including antagonist ...
, and
nicotine
Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
. Despite these findings, the insula has been ignored within the drug addiction literature, perhaps because it is not known to be a direct target of the mesocortical
dopamine
Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...
system, which is central to current dopamine reward theories of addiction. Research published in 2007 has shown that
cigarette
A cigarette is a narrow cylinder containing a combustible material, typically tobacco, that is rolled into thin paper for smoking. The cigarette is ignited at one end, causing it to smolder; the resulting smoke is orally inhaled via the opp ...
smokers suffering damage to the insular cortex, from a
stroke
A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...
for instance, have their addiction to cigarettes practically eliminated. 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. The study was conducted on average eight years after the strokes, which opens up the possibility that
recall bias
Recall may refer to:
* Recall (bugle call), a signal to stop
* Recall (information retrieval), a statistical measure
* ''ReCALL'' (journal), an academic journal about computer-assisted language learning
* Recall (memory)
* ''Recall'' (Overwatc ...
could have affected the results. More recent prospective studies, which overcome this limitation, have corroborated these findings This suggests a significant role for the insular cortex in the neurological mechanisms underlying addiction to
nicotine
Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
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
Lithium chloride is a chemical compound with the formula Li Cl. The salt is a typical ionic compound (with certain covalent characteristics), although the small size of the Li+ ion gives rise to properties not seen for other alkali metal chlor ...
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 is 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 addictive psychoactive drugs. 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.
Subjective certainty in ecstatic seizures
A common quality in mystical experiences is a strong feeling of certainty which
cannot be expressed in words. Fabienne Picard proposes a neurological explanation for this subjective certainty, based on clinical research of epilepsy.
According to Picard, this feeling of certainty may be caused by a dysfunction of the anterior insula, a part of the brain which is involved in
interoception, self-reflection, and in avoiding uncertainty about the internal representations of the world by "anticipation of resolution of uncertainty or risk". This avoidance of uncertainty functions through the comparison between predicted states and actual states, that is, "signaling that we do not understand, i.e., that there is ambiguity." Picard notes that "the concept of insight is very close to that of certainty," and refers to Archimedes' "Eureka!" Picard hypothesizes that during ecstatic seizures the comparison between predicted states and actual states no longer functions, and that mismatches between predicted state and actual state are no longer processed, blocking "negative emotions and negative arousal arising from predictive uncertainty," which will be experienced as emotional confidence.
[Picard 2013, p.2498] Picard concludes that "
is could lead to a spiritual interpretation in some individuals."
Other clinical conditions
The insular cortex has been suggested to have a role in anxiety disorders, emotion dysregulation,
and
anorexia nervosa
Anorexia nervosa, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gr ...
.
History
The insula was first described by
Johann Christian Reil
Johann Christian Reil (20 February 1759 – 22 November 1813) was a German physician, physiologist, anatomist, and psychiatrist. He coined the term psychiatry – ''Psychiatrie'' in German – in 1808.
Medical conditions and anatomical featur ...
while describing cranial and spinal nerves and plexuses.
Henry Gray
Henry Gray (1827 – 13 June 1861) was a British anatomist and surgeon most notable for publishing the book ''Gray's Anatomy''. He was elected a Fellow of the Royal Society (FRS) at the age of 25.
Biography
Gray was born in Belgrav ...
in
Gray's Anatomy
''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter, and first published in London in 1858. It has gone through multiple revised editions and the current edition, the 42nd (Octob ...
is responsible for it being known as the ''Island of Reil''.
John Allman
John Morgan Allman is an American neuroscientist at the California Institute of Technology in Pasadena, California, active in the fields of primates, cognition and evolutionary neuroscience.
Life
He graduated from University of Chicago with a ...
and colleagues showed that anterior insular cortex contains
spindle neurons
Von Economo neurons (VENs), also called spindle neurons, are a specific class of mammalian cortical neurons characterized by a large spindle-shaped soma (or body) gradually tapering into a single apical axon (the ramification that ''transmits ...
.
Additional images
File:Gray731.png, The insula of the left side, exposed by removing the opercula.
File:Gray743.png, Coronal section through anterior cornua of lateral ventricles.
File:Telencephalon-Horiconatal.jpg, Horizontal section of left cerebral hemisphere.
File:Insular_cortex.gif, 3D view of the insular cortex in an average human brain
File:Insular cortex coronal sections.gif, Insular cortex highlighted in green on coronal T1 MRI images
File:Insular cortex sagittal sections.gif, Insular cortex highlighted in green on sagittal T1 MRI images
File:Insular cortex transversal sections.gif, Insular cortex highlighted in green on transversal T1 MRI images
See also
* List of regions in the human brain
References
External links
* . Location and literature citations for the insula
*
*
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*
{{DEFAULTSORT:Insular Cortex
Homeostasis
Human homeostasis
Cerebral cortex