Emotion

Emotion is a complex, multi-dimensional phenomenon that encompasses a range of psychological states and physiological responses^[1]. It involves components such as subjective experiences, cognitive processes, expressive behaviour, psychophysiological changes, and adaptive responses^[2].

Emotions can be understood as a part of the brain's "guidance system" for managing our behaviour and interactions with the environment^[3]. From an evolutionary perspective, emotions can be seen as adaptive responses to stimuli in the environment that have significant implications for survival and reproduction^[4].

Fear, for instance, prompts avoidance or escape behaviour in response to threats, while happiness or pleasure encourages approach behaviour towards beneficial or rewarding stimuli^[5]. Social emotions like empathy or shame facilitate group cohesion and cooperation, essential for social species such as humans^[6]. Emotions like anger may help deter exploitation by others^[7]. By shaping our behaviour in these ways, emotions have contributed to the survival of our ancestors and have been naturally selected over generations^[8].

While there's considerable debate among psychologists about the number and types of emotions that humans experience, psychologist Paul Ekman identified six "basic" emotions that he suggested were universally experienced in all human cultures. These are happiness, sadness, disgust, fear, surprise, and anger^[9]. Robert Plutchik, another prominent researcher, proposed a slightly different set of eight primary emotions: joy, sadness, trust, disgust, fear, anger, surprise, and anticipation^[10].

1. Happiness/Joy: This is often described as the experience of contentment or satisfaction. It is associated with a state of well-being and fulfilment^[11]. The function of joy is to signify that current circumstances are desirable and goals are being achieved, leading to a relaxation of defences and a tendency towards playfulness and social engagement^[12]. It is generally associated with increased dopamine and serotonin levels in the brain^[13].

2. Sadness: This emotion is characterised by feelings of loss, helplessness, disappointment, or despair. Evolutionarily, it is thought to signal a need for help or support, leading to increased social bonding and cooperation^[14]. It is generally associated with decreased serotonin and increased cortisol levels^[15].

3. Disgust: This emotion typically occurs in response to something offensive, repulsive, or distasteful. From an evolutionary perspective, disgust helps to avoid harmful or unpleasant substances or situations^[16]. It triggers a strong desire to withdraw from the source of the unpleasantness^[17].

4. Fear: Fear is the emotional response to a real or perceived imminent threat. It triggers the body's fight-or-flight response to prepare for or avoid danger^[18]. Fear can be a protective mechanism that helps one respond quickly in dangerous situations^[19]. Fear is associated with the amygdala and can lead to increased adrenaline and cortisol levels^[20].

5. Surprise: This emotion is often experienced when encountering an unexpected event or situation. Surprise itself is neutral and can lead to either positive or negative emotions, depending on the context^[21]. It serves to focus attention on a new, unexpected event which could be potentially important^[22].

6. Anger: This emotion can occur when we face an obstacle, perceive an injustice, or experience a threat. It prepares the body to fight and remove the obstacle; however, it can also lead to aggression if not managed appropriately^[23].

7. Trust: Trust is an emotion that arises with the expectation of positive outcomes from others. It serves to build and maintain social relationships and can lead to feelings of security and safety^[24].

8. Anticipation: Anticipation involves looking forward positively to a future event or situation. It often motivates behaviors to achieve the anticipated outcome. This emotion can help in planning and decision making^[25].

While these emotions are often categorised as 'basic' or 'primary,' humans experience a wide array of complex and nuanced emotions, often blends of these basic ones, and these can be dependent on individual experiences, culture, and social context^[26]. The ability to recognise and express these emotions plays a crucial role in human communication and social interaction^[27]. The capacity to understand and empathise with others' emotions is an essential aspect of emotional intelligence.

Feeling an emotion such as happiness is a multi-step process that includes several stages: the perception of a stimulus, the appraisal and interpretation of the stimulus, physiological and neural responses, the conscious experience of the emotion, and, finally, possible behavioural responses^[28].

Here's a simplified breakdown of these stages:

• Perception of Stimulus: The process begins with the perception of a stimulus. This could be anything from a physical object to a social event, a memory, or an idea^[29]. For example, you may receive a positive message from a close friend.

• Appraisal of Stimulus: The next step is the appraisal and interpretation of the stimulus^[30]. This is where your brain interprets the situation and assigns meaning to it. Your cognitive systems, informed by past experiences, current mood, and the social context, decide whether the stimulus is positive, negative, or neutral^[31]. In our example, you recognise the message as positive and meaningful.

• Physiological and Neural Responses: Following the appraisal of the stimulus, the brain triggers a series of physiological responses^[32]. The limbic system, particularly the amygdala and the hippocampus, plays a significant role in this process^[33]. The hypothalamus activates the reward circuit in the brain, including the ventral tegmental area (VTA), nucleus accumbens, and prefrontal cortex, which leads to the release of neurotransmitters like dopamine and serotonin that are associated with pleasure and mood regulation^[34].

• Conscious Experience of Emotion: Following these physiological and neural changes, the subjective feeling of happiness emerges^[35]. This conscious emotional experience also involves various areas of the brain, including the insular cortex (involved in emotional awareness) and the anterior cingulate cortex (involved in focusing attention on important emotions)^[36].

• Behavioural Response: Finally, the emotion of happiness often leads to specific behaviours or expressions^[37]. This could include physical responses such as smiling or laughing, as well as more complex behaviours such as reaching out to share the good news with others.

The emotional process is not strictly linear; many of these steps may happen simultaneously, and feedback between them is continuous^[38]. For example, the physical feeling of smiling can enhance the feeling of happiness, and the conscious experience of happiness can alter how you continue to appraise the situation^[39].

The neurobiology of emotions involves several neurotransmitters and brain regions^[40].

Neurotransmitters: A variety of neurotransmitters and hormones play a role in the generation and regulation of emotions:

• Serotonin: Often called the 'feel good' neurotransmitter, it plays a key role in mood regulation. Imbalances in serotonin can lead to mood disorders like depression and anxiety^[41].

• Dopamine: Known as the 'reward' neurotransmitter, it's linked with feelings of pleasure and reward. Dopamine is also integral to motivation^[42].

• Norepinephrine: Plays a role in the body's stress response and is associated with the fight or flight response, leading to increased heart rate and blood pressure^[43].

• GABA (gamma-aminobutyric acid): An inhibitory neurotransmitter that can reduce anxiety and promote feelings of calm^[44].

• Glutamate: An excitatory neurotransmitter that plays a role in the perception and generation of emotions^[45].

• Oxytocin: Known as the 'love hormone', it's associated with social bonding, trust, and empathy^[46].

• Endorphins: Often released during stress or pain, they can promote feelings of pleasure or euphoria^[47].

• Cortisol: Known as the 'stress hormone', it's released during high-stress situations or in response to a perceived threat^[48].

Brain Regions: Several key brain regions and structures are involved in the processing and regulation of emotions.

• Amygdala: This almond-shaped structure in the brain is heavily involved in emotion processing. It plays a crucial role in generating emotional responses, particularly in relation to fear and pleasure. The amygdala is critical in determining which events are significant and require a heightened emotional response. It's also involved in the processing of emotional memories, allowing an individual to create an emotional context for experiences. This functionality of the amygdala is part of the reason why certain events or experiences can trigger strong emotional responses^[49].

• Hippocampus: This region of the brain, while primarily known for its crucial role in forming new memories, also has a substantial role in emotion. It provides the context for emotional experiences, by attaching emotional significance to memories. When an event occurs, the hippocampus helps recall the memories and emotions associated with similar past experiences, essentially giving emotional meaning to current events^[50].

• Prefrontal Cortex (PFC): This region of the brain is primarily involved in higher-order functions such as decision making, planning, and moderating social behaviour. In terms of emotion, the PFC has a role in the cognitive evaluation and regulation of emotions. This includes assessing the significance of an emotional stimulus and generating an appropriate emotional response. The PFC is also involved in inhibiting emotional responses when necessary. Dysfunction in the PFC can lead to difficulties with emotional regulation, impulsivity, and decision-making^[51].

• Anterior Cingulate Cortex (ACC): This region of the brain is thought to play a key role in emotion. Specifically, the ACC is involved in evaluating emotional response to pain and monitoring for conflict (the presence of competing information or demands). The ACC also contributes to decision-making and impulse control, both of which are closely related to emotional responses^[52].

• Insular Cortex (insula): The insula is involved in the conscious awareness of emotions and is critical to our subjective emotional experience. It plays a significant role in the experience of a wide range of emotions, including disgust, happiness, and sadness. The insula is also associated with the experience of empathy, providing a sense of understanding and sharing the emotions of others. Furthermore, the insula has been implicated in interoceptive awareness – the awareness of the physiological condition of the body, such as feeling your heartbeat, which is crucial for many emotional experiences^[53].

These regions, along with other areas of the brain and the complex interplay between them, work together to generate, process, and regulate our emotional experiences. The complex interplay between these neurotransmitters, brain regions, and autonomic responses results in the wide range of emotional experiences that we have as human beings.