Motivation and emotion/Book/2022/Insular cortex and emotion

Overview
Emotions play a significant role in our everyday lives. Whether you are happy, sad, angry, surprised, disgusted, afraid or frustrated. Emotions influence our decision-making, promote action, allow us to connect with others, guide our behaviour and empower us to grow. But how do these emotions manifest? And what structures are involved in emotional expression, understanding and awareness?

The emotional system of the brain is incredibly complex. The primary structures that have been recognised as key contenders in emotion are the prefrontal cortex, amygdala, hippocampus, anterior cingulate cortex and insular cortex (Huppert, 2009). These brain regions work in alliance to process and produce emotional information.

The insular cortex also known as the "insula" or "Island of Reil" was initially discovered by the German neurologist, Johann Christian Reil in the 19th century (Gogolla, 2017). Upon its discovery, Reil had thought the insular cortex was central to mental processes. Whilst this conclusion hasn't since been supported, it has been found that the insular cortex plays an instrumental role in a variety of emotions and their interpretation. This chapter investigates the role the insular cortex plays in emotions. Discussion of relevant psychological theory and research is presented. Knowledge of the role of specific brain regions, in this case, the insular cortex and its role in emotions are important in understanding the underlying functions of emotion.

Focus questions:
 * What are emotions?
 * What is the anatomy of the insular cortex?
 * What types of emotions are the insular cortex involved in?
 * What is the James-Lange theory of emotion and how does it relate to the insular cortex?
 * What is the impact on emotion if the insular cortex is damaged?

What are emotions?


The definition of emotion is often ambiguous and a widely debated concept within psychological research. A generally accepted definition of emotion is that they are complex, short-lived responses involving biological and physiological states where neural activity is responsible for emotional processing (Izard, 2009). Emotions are motivators which trigger urges leading to action to achieve a specific goal (Reeve, 2018). Positive and pleasant emotions include but are not limited to happiness, joy, satisfaction, interest, empathy and curiosity (see Figure 1). Negative emotions, whilst unpleasant, are central to the human experience and are unavoidable. These may include anger, sadness, frustration, disgust, frightened, guilt and envy.

The underestimated insular cortex
The insular cortex is an area of the brain where very little is understood about it. Due to the insular cortex's deep localisation and dense vascular networks made it challenging for researchers to explore this area (Rachidi et al., 2021). As a result, it was an often ignored and neglected region of the brain. Originally, scientists believed that the insular cortex was a section of the visceral region of the brain. It wasn't even considered notable enough to be included in Brodmann's famous map of the cerebral cortex (Droutman, 2015).

Since then, research has expanded. The insular cortex has become a hot topic of exploration in the neuroscience field. The insular cortex is now recognised as a limbic-related cortex. As research has progressed, the insular cortex is known to be a key and crucial participant in sensorimotor processing, cognitive functions, decision-making, emotions and subjective feelings (Uddin et al., 2017). Therefore, making the insular cortex a notable area of the brain to investigate. Particularly when wanting to understand more about the underlying functions of emotion.

Anatomy of the insular cortex


The insular cortex is found within the cerebral cortex. Due to it being hidden far within the lateral sulcus, the insular cortex is not viewable from the outside of the brain (Gogolla, 2017) (see Figure 2). It has a complex vascularisation system and is located beneath thick arteries and venous blood vessels (Uddin et al., 2018). Making accessibility to this brain region particularly difficult. The insular cortex is also linked with a variety of large brain systems. It connects with subcortical and cortical regions such as the hypothalamus, basal nucleus, periaqueductal grey, amygdala, anterior cingulate, orbitofrontal cortex and medial prefrontal cortex (Gogolla, 2017). These areas of the brain are involved in cognition, motivation, emotion and sensory and executive functions such as planning, attention and multitasking (Gogolla, 2017).

The insular cortex is made up of two main sections: the anterior insular cortex and the posterior insular cortex (Geunot et al., 2008). The anterior insular cortex is built up of three gyri: the anterior gyri, the middle gyri and the posterior short insular gyri (Geunot et al., 2008). Whereas, the posterior insular cortex is comprised of the anterior long insular gyri and the posterior long insular gyri (Geunot et a., 2008). Due to the insular cortex being a complex area of the brain, this chapter mainly focuses on the anterior and posterior insular cortex and their unique roles in emotion.

What emotions are the insular cortex involved in?
The insular cortex is involved in the processing and moderating of a variety of negative and positive emotions (Gogolla, 2017). These emotions range from unpleasant feelings of disgust to pleasant emotions of love and sexual arousal (see Table 1).

Table 1.

Areas of the insular cortex and their role in emotion

Disgust


Consider the last time you went to make a cup of coffee or tea and reached into your fridge to grab the milk. You contemplate how long the milk has been in the fridge and open it up to be met with a repugnent scent. You may have experienced nausea, repulsion, antipathy and nose wrinkling in response to smelling the sour milk (See Figure 3). Disgust is known as strong feelings of repulsion to an offensive substance and is connected with rejection and distancing one's self from a revolting stimulus (Olatunji & Sawchuk, 2005). Many studies have demonstrated activation in the insular cortex and amygdala in response to disgusting odours and tastes (Wicker et al., 2003). As well as activation of the insular cortex when participants observed facial expressions of disgust. So, how does the insular cortex process the emotion of disgust? It is thought that the insular cortex is involved in decision-making. It encourages us to either approach the disgust-related stimulus or avoid and move away from the disgust-related stimulus (Suzuki, 2010).

Anxiety
Whilst it is currently unclear how the insular cortex is involved in anxiety. The insular has been implicated in a variety of anxiety-related behaviours and disorders. Research has shown a relationship between people with obsessive-compulsive disorder, simple phobia or post-traumatic stress disorder and an increase in cerebral blood flow in the insular cortex (Rauch et al., 1997). It has been found that individuals who are susceptible to anxiety have an altered interoception prediction signal compared to non-anxious people (Paulus & Stein, 2006). It is possible that people who are anxiety-prone perceive their bodily state negatively. This then triggers an increase in anxious thoughts and avoidant behaviours. It is thought that the anterior insular cortex is a key brain region involved in this process (Paulus & Stein, 2006). However, it is important to recognise that an altered interoception prediction signal has not yet been examined across other anxiety-related disorders which would be an interesting area to examine further.



Sexual arousal & love
Everyone loves love. The insular cortex certainly does. The insular cortex is involved in feelings of sexual arousal, desire and romantic love (see Figure 4). Research reviewing fMRI studies investigated what brain regions were associated with love and sexual desire. They discovered that the anterior insular was activated strongly by feelings of love, whereas the posterior insular was activated with feelings of sexual desire and lust (Cacioppo et al., 2012). What these findings indicate is that the anterior insular is a crucial participant in recognising feelings of love and contributing to feelings of love but is not involved in feelings of sexual lust or desire.

Empathy
Empathy is known as the ability to share and understand the emotions, experiences and thoughts of others. Empathy is an important emotion for social behaviour and there is various evidence which recognises the insular cortex's role in empathy and in particular the anterior insular cortex's involvement.

Picture this, your friend's dog has just passed away. You go over to their house and bring chocolates and flowers to show your support. When you get there, your friend's eyes are puffy, and red and they are crying. In response you begin crying and feel the emotion of sadness. Here you are showing emotional empathy and your insular cortex is activated during the experience of this emotion.

The anterior insular cortex has been investigated concerning empathetic experiences of pain. Activation in the anterior insular cortex was consistently observed when research participants experienced pain themselves and when participants observed pain in others (Singer et al., 2009).

More recent research by Mutschler et al. (2013) has confirmed the positive association between the insular cortex and empathy. According to these researchers, the anterior insular cortex is the only area of the brain to have consistent links "with all emotional, attentional, cognitive, intentional, perception, sensational awareness, motor perception, empathy-related tasks leading to the formulation of a domain-general region for empathy in the AIC" (Mutschler et al., 2013). It is safe to say that the anterior insular cortex's involvement in empathy is stable and is consistent across emotional and cognitive functioning.

James-Lange theory of emotion


The James-Lange theory is one of the earliest theories of emotion. It was proposed by William James and Carl Lange in 1884 (Cannon, 1987). The theory posits that emotions are a result of physiological or your bodies responses to emotionally-stimulating events (Reeve, 2018). Emotions are a by-product of bodily responses rather than the bodily responses being a result of an emotion. Your brain doesn't just make decisions based on what you are seeing, touching, tasting and smelling and then tells the body to respond emotionally. Rather, your brain receives and interprets information from your environment and before you are consciously aware of this information, the body is already responding by changing the state of the body. You are then able to consciously conclude that you are feeling a specific emotion. For example, when your heart begins to race before presenting an oral presentation your brain can interpret this information and then can label the emotion as anxiety (see Figure 5).

Interoception
The insular cortex is responsible for interoception. Interoception is your awareness of sensations happening within your body. Interoception can be unconscious or conscious, this is known as interoceptive awareness (Price et al., 2018). Interoceptive awareness could be recognising that your heart rate or breathing rate getting faster or slower in response when experiencing feelings of love when seeing your partner at the end of the day. It is thought that the insular cortex develops emotional awareness or an interoceptive view of a person's physiological state to then initiate subjective feelings (Gu et al., 2013). This is related to James-Lange's theory of emotion as it implies that the insular cortex will first process and interpret a person's physiological state before a person consciously experiences an emotion.

Table 2.

Process of interoception in the insular cortex (Namkung et al., 2017)

Damage to the insular cortex
We are now aware that the insular cortex plays a significant role in the interpretation of emotion. So what happens to our emotions if the insular cortex is damaged? The insular cortex is involved in trust, disgust and emotional awareness so it is a concern when damage is present in this area. Research has shown that these emotions are all harmed by damage to the insular. Lesions to the insular cortex have an impact on a person's ability to recognise emotional facial expressions. In particular, the emotion of disgust (Motomura et al., 2019).

Some research has discovered that damage to the right insular cortex has an impact on a person's ability to recognise their own emotions and the emotions of others, no matter the type of emotion (Terasawa et al., 2015). Not only is recognition of emotion an issue with damage to the insular, but people with damage in this area may experience issues in their social relationships. For example, a study by Belfi et al. (2015) showed that people with damage to the insular cortex showed abnormal expressions of trust. These people were more likely to show trust for their partner even if their partner had betrayed their trust. Furthermore, people with damage to the insular cortex had a tended to betray their partner's trust even when their partner had shown trust. What all this evidence indicates is that the insular cortex is implicated in emotion so much so that when damaged it has drastic emotional consequences.



A 25-year-old male known as NK experienced damage to the insula through a selective left middle lesion. NK demonstrated an impaired ability to recognise disgust and a slight deficit in recognising surprise when shown facial signals and non-verbal emotional sounds. NK was also less disgusted than the control group when experiencing disgust-inducing scenarios. (Terasawa et al., 2015)

Have you been paying attention?
Select your answers and then press submit. The insular cortex was historically neglected and disregarded by scientists: + True - False
 * type=""}

{The insular cortex is involved when: - Your mood needs a boost when you are sad + You are watching a friend eat a food you are repulsed by - You recall an emotional memory - You need to find the motivation to do your homework
 * type=""}

{It has been found that the posterior insular cortex activates when: - Experiencing feelings of disgust + Experiencing feelings of lust and sexual desire - Experiencing feelings of love - Experiencing feelings of aggression
 * type=""}

{In the case of NK, what did he have difficulty doing? + Recognising disgust - Recognising if a person is attractive or not - Recognising whether a stimulus is threatening - Recognising if someone is sad
 * type=""}

{Anxiety-prone individuals have altered interoceptive prediction signals + True - False
 * type=""}

Conclusion
The insular cortex is an amazingly complex structure which has been demonstrated to play a significant role in a variety of emotions. Current research contends that the insular cortex can no longer be recognised as a redundant area of the brain by researchers. The insular cortex is worth researching further when wanting to know more about the brain and emotional experience. From the positive experiences of love and sexual arousal to negative experiences of disgust, the insular cortex is a key participant in processing, interpreting and recognising emotions. The James-Lange theory of emotion provides a framework to understand the interoceptive ability of the insular cortex. Damage to the insular cortex has been shown to have harmful effects on a person's ability to recognise specific emotions and results in deficits in social emotions. Next time you taste something disgusting that your Mum has cooked or when you feel trust towards your partner remember that your insular cortex is working hard to process and recognise these emotions.