Motivation and emotion/Book/2018/Insular cortex and emotion

Overview


The insular cortex (IC) is part of the prefrontal cortex (PFC) of the brain (see figure 1). The primary role of the IC is monitoring bodily feelings both physical and psychological. It then communicates that information to other regions of the brain (Reeve, 2018). The IC is important in the formation of emotion because it uses physical feelings to create emotional feelings. There are currently significant amounts of research aimed at improving the understanding the functionality of the IC. The IC uses various sensory processes and sensory memory, to guide an appropriate response based on many inputs (Hurtado, García, & Puerto, 2016).

In events where all stimuli are not accessible, the individual is incapable of making an accurate decision. If key information is missed, the individual will act in a way that is socially inappropriate. The most relatable bodily sensations the IC uses are the sensations of heart, stomach and taste.

The IC monitors and alters sensations (Caria et al. 2007). Most sub-regions of the brain have a unique function. The IC has two primary sub-regions which work together and also independently, which are, posterior insular cortex (pIC) and the anterior insular cortex (aIC). This chapter will investigate the ICs influences in the formation of emotion. The IC, not only monitors these sensations but also relates any these changes to regions that can make appropriate alterations to keep the organism alive.

Theory and research
As studies of the IC have only been around in the last few decades, new research often finds evidence that proves old research considerably wrong. Initially it was believed that the entire IC is always activated together; however, in the last decade there is increasing evidence that sub regions of the IC work independently. As technology improves, smaller areas of the brain can be studied in greater detail, which increases the rate of understanding of the brain. There are no two brains that are identical in neural connections in the world, which makes comparing brains not very useful as there are far too many variables. Finger-print studies are now used to allow the ability to qualitatively describe a single individual's functional repertoire of the brain (Uddin et al. 2014, pp 20 – 21).

Small subsections of the IC communicate effectively with other regions of the brain. Uddin (2014) studied the neural activity of the aIC or pIC when a participant is completing certain tasks in a Functional Magnetic Resonances Imaging (fMRI) procedure. It showed there is distinctive simultaneous activity from only small subsections, which means the whole IC does not always activate together. It was concluded the IC has three functional sub-regions with their own distinct functionality, the dorsal anterior IC, ventral anterior IC and posterior IC. This study is significant as it explains different regions are more independent; For example, the pIC co-activates with regions such as the somatosensory cortex (Moraga-Amaro & Stehberg, 2012).

Drugs influence the insular cortex's ability to form emotion
The IC is one of the most interconnected regions of the brain and is needed to feed sensory information to the limbic region to ultimately form emotion, which results in vulnerabilities to manipulation and misinterpretation (García, Simón, & Puerto, 2013). All drugs alter the brain in different ways, however, some drugs like illicit ones can cause permanent changes through altering the neurochemistry in the brain. This can cause changes in personality and emotion. Studies slightly differ in exact regions of activation on connectivity that is affected, however the trend overall is very similar.

The IC monitors the body, so when a drug is introduced it must adjust the body and its understanding of the body. The aIC has a significant number of pathways to the amygdala in comparison to other regions, which increases the likelihood of the amygdala also becoming affected by a drug. Selective serotonin reuptakes inhibitor (SSRI) directly affect the amygdala and mildly affect the IC in emotion formation process, such as Escitalopram (Arce, 2008).

Some sensations are more influential than others
Pain is a strong motivator in how an individual acts. During a painful experience, the pIC activates at the same time as the cingulete cortex (CC); the CC is located just in front of the corpus callosum. The CC is involved in motivation, action and learning. The IC activates when the body feels pain, to establish the type and location (Lenoir, Algoet & Mouraux, 2018). It then sends the processed information to other regions of the brain to find a way stop or avoid the pain. There is a considerable number of studies to investigate ways to alter the IC’s perception of pain.

A study by Barthas et al. (2015) investigated how the IC monitors emotional and physical sensations, and more specifically the long term resulting damage on neurological activity. Rats in the study had surgically created lesions in the anterior CC, to create neuropathic pain (nerve pain). The study made two interesting findings, firstly the pIC has no direct relationship to emotion; instead it activates the somatosensory cortex and other regions of the brain. Secondly, they found evidence that chronic and severe pain can cause long term and possibly permanent changes in pathways between pIC and the anterior region of the CC (Barthas et al, 2015).

Subconscious to conscious
The brain processes large amounts of information on a subconscious level, while only a very small percentage becomes conscious; as the brain can not process all information on a conscious level effectively. Sensory input in the brain is prioritised such that important information has a lower latency. Priority of latency is dependent on interoception, which is the monitory process of sensory output in the body such as temperature and pain. Pain has a low latency and is dealt with immediately (Sridharan, Levitin & Menon, 2008).

The aIC is considered as being discriminate against positive emotion in speech. A study by Chen, Lee  & Cheng (2014) researched this theory using recorded voices; the recordings varied from monotone voices to happy, disgust and anger. The study established that there is a higher frequency of activation with the disgust voices, which suggests disgust is an emotional response the IC recognises. The study stated that further research is needed to establish whether the activation is only with certain negative voices and stimuli, for example when an individual is angry.

Social information processing following resection of the insular cortex
A study by Olivier Boucher and Colleagues

As research continues to understand the functions of the IC, it is becoming more evident the IC is needed in the process of turning basic stimuli such as a facial expression into an emotion. If an individual sees their friend has an angry expression they will feel upset or anger themselves, dependent on the situation.

A study by Broucher (2015) investigated how much influence the IC has over the formation of emotion from physical stimuli. The study has three conditions; Group 1: epileptic individuals, who have complete partial removal of IC; Group 2: individuals with no brain damage or surgery and Group 3: epileptic individuals with partial removal of the temporal lobe. All participants underwent a battery of tests of emotional intelligence and recognition of emotion (Broucher et al. 2015).

In one exercise the participants were shown faces with various expressions and they were asked to identify the emotion displayed. Group 1 scored lower than the other groups; in particular they had difficulties in recognition of fear, surprise and happiness. Group 3 showed lower scores in recognition of fear. In another exercise where the expressions of the participant are noted, it was evident Group 1 have difficulty displaying some emotions such as anger (Broucher et al. 2015).

It is evident in this study that the IC does discriminate against certain emotions; however, the study concluded the results indicate the IC recognises a greater range of emotions than previously thought. Notably, Group 3 had equally as low scores as Group 1, for questions of semantic memory. It was concluded, the reason Group 3 scored low, is most likely a result of damage to the limbic region during surgery (Boucher et al. 2015).

The insular cortex and the amygdala need each other
The amygdala (see figure 2) is very close in space to the IC and is involved in the Fight or Flight or Freeze Response as a coping mechanism for a stressful situations. The amygdala is well recognised as the part of the brain that deals with stress. When the body is in a high emotional state, the brain takes in and remembers more information. A study by Beldjoud, Barsegyan and Roozendaal (2015) investigated whether the higher levels of stress increase memory through first injecting synthesised norepinephrine directly in rats and to ensure a stressed state, immediately the rats were taught a maze. The control group learnt the maze without the injection of noradrenergine. The test group learnt the maze faster than the control group, which is evidence that the amygdala and the IC must be communicating because the IC uses the stressed state more effectively ( Beldjoud, Barsegyan & Roozendaal, 2015). The IC and amygdala must have a significant activation together for this process to take place.

Autism Spectrum Disorder
There are many disorders and illnesses the IC is involved in. Autism Spectrum Disorder (ASD) affects large areas of the brain and is a life long disorder. Autistic individuals have difficulties with comprehension and communication skills, due in part to low connectivity from the IC to the limbic region. This results in deficits in comprehension and communication due to difficulties with reading facial expressions, which is referred to as Imitation. (Colombi et al. 2009).

The severity of the disorder can be vastly different for each person, and as such, the spectrum concept works as a measure. An individual on the lower end is highly affected by the disorder and is likely to be unable to speak and will find many situations confusing; whereas an individual on the higher end is average to highly intelligent with difficulty interacting in some social situations (Nuske, Vivanti, & Dissanayake, 2013).

ASD patients have difficulty with Salience monitoring because information that is important in a social setting is missed or incorrectly interpreted. This results in situations where people on the spectrum miss social cues such as sarcasm, because tone of voice and subtle social stimuli can be missed all together (Uddin, 2015).

It is widely accepted the aIC is more affected than the pIC (Uddin & Menon, 2009). A common misconception of ASD patients is an inability to feel empathy. A study of individuals with ASD showed that amygdala reactivity is close to typical function. This indicates that while ASD allows recognition of emotion, empathetic responses are limited due to impaired imitation abilities (Dapretto et al. 2006). An autistic individual can feel empathy, but has difficulty communicating an empathetic response.

Test your knowledge so far
Choose the correct answers and click "Submit": {What is the main functions of the IC? (May be multiple answers). - Monitors only sense of touch. - Directly transfers sensory information to emotion. + Part of the process of forming an emotional response.
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{What region of the brain is the insular cortex located?. - Limbic + PFC - Temporal
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{What is the current trend in research? +Researchers are finding more emotions the IC recognises. - Autistic people don't try hard enough to communicate. -IC only does what other regions do anyway.
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Improvements in current research
Currently it is understood that the IC is highly involved in using previous experiences as a bench mark to react to a situation. There IC may hold a the reason into why negative memories are highly influential. Further research needs to investigates why the IC favours certain memories over others.

Currently it is understood that different stimuli is needed to form emotion in different regions of the brain. The current understanding is the IC recognises negative tones in speech, while in facial expression the IC tends to notice more positive emotions. Further research will benefit by understanding exactly what these differences and why.

Psychological disorders can alter salience, for example individuals with Schizophrenia have weaker pathways between the aIC and the anterior CC due to higher levels of Dopamine, which causes delusions (White, Joseph, Francis & Liddle, 2010).

Conclusion
The IC is critical in the brain as it is a method to keep unimportant stimuli in the subconscious. When the IC does not process information correctly, an individual is unable to comprehend and respond to a situation. The IC notices emotions other regions of the brain do not, such as happiness. The IC is needed to interpret the basic stimuli of a situation, such as sound and facial expressions. An individual can live a functional life with emotions, but without the IC they will not have a full range because basic stimuli needed to form emotions will not be noticed.