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Amy,¹ a 17-year-old patient of mine, is an intelligent young woman who is about to start an engineering program at a top Canadian university. But, frustratingly and distressingly for her, she has always had difficulties with emotional regulation, manifesting as a propensity toward high levels of anxiety, oversensitivity, and low frustration tolerance. In her interactions with family, she is prone to “meltdowns” and not infrequently explodes in temper outbursts. Outside of the home, she usually bottles things up, holding her emotions in until she gets home, often on the verge of tears. Her angry verbal outbursts toward her parents can be particularly nasty. These tirades are frequently followed by remorseful apologies, tearfully insisting that she did not mean what she said. Despite these difficulties, Amy has managed to do well academically and maintain a few close friendships. But controlling her emotions requires an exhausting amount of effort, and they always threaten to derail her.

Amy’s emotional difficulties are more severe than the average person's. But all of us can relate to the experience of having our emotions erupt from somewhere deep within us and upend our attempts at remaining composed, rational, and self-controlled.

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What actually are they?

So, what are emotions? Most of us think we know, since we are routinely and intimately acquainted with them.

Surprisingly, to this day, there is no scientific consensus on what emotions are, and where in the brain they are produced. Among the areas of continuing disagreement are whether or to what degree emotions are the product of deep, ancient subcortical brain circuits or more dependent on evolutionarily newer cortical regions, how widespread emotions are in the animal kingdom, and the relation between emotions and consciousness. This four-part blog series will attempt to delineate and explain the different contemporary positions.

Emotions versus feelings

In everyday conversation, the term "emotion" is commonly used synonymously with "conscious experience of emotion" or "feeling." However, scientists generally consider emotions to be automatic, unconscious physiological and behavioral reactions to stimuli.² Feelings, in contrast to emotions, are the conscious awareness and subjective interpretation of these bodily reactions, shaped also by personal experience and culture. Scientists differ in the relative emphasis they place on conscious feelings versus automatic emotions, and on the degree to which feelings might be uniquely "constructed” in the brains of different individuals.

Delineating and researching emotions

There are both dimensional and categorical approaches to understanding emotions.

Emotions can be represented along two dimensions: valence (pleasantness to unpleasantness) and intensity (low to high arousal), known as "core affect" in psychological theories.³

Categorical approaches view emotions as occurring in several distinct primary forms, e.g., joy, fear, anger. They can also be categorized into complex secondary emotions that regulate social or moral behaviors, such as shame, guilt, embarrassment, pride, and jealousy. There is ongoing debate about whether these commonly used categories will be borne out by ongoing neuroscientific research, and about their universality.

Most psychological studies of emotion in humans have focused on the everyday sense of “emotion” as synonymous with "feeling" (i.e., conscious experience of emotion). But animal research is focused on behavioral or physiological responses, as animals cannot report feelings. An empirical approach to research thus treats emotions as central brain states that can be studied in both humans and animals, whereas feelings can only be self-reported by humans. Some researchers (e.g., Joseph LeDoux, discussed in part 4) caution strongly against assuming that similarities in behavioral or physiological responses between animals and humans imply that animals experience similar feelings to us. Feelings cannot be reliably inferred from behavior.

Emotions play a central role

Emotions are crucially important for human behavior. They integrate feelings, physiology, and sensorimotor behavior.⁴ They provoke a wide range of physiological responses throughout the body, including changes in heart rate, hormone levels, and immune function. They affect arousal and cognition, including attention, memory processing, and decision-making. They profoundly affect motivation. Emotions also play a significant role in learning, by reinforcing associations through positive and negative reinforcement. Additionally, emotions contribute to social interactions and communication, impacting how we connect with others and navigate social environments. Thus, they can influence our immediate actions and affect our behavior over longer periods.

More complex than reflexes but simpler than deliberative behavior

The authoritative textbook Principles of Neural Science, in its chapter on emotion, provides the following definition:

“Emotions are neurobiological states that cause coordinated behavioral and cognitive responses triggered by the brain. This can occur when an individual detects a significant stimulus (positively or negatively charged) or has a specific thought or memory that leads to an endogenously generated emotional state.”⁵

Emotions play an intermediate role in regulating the body's physiology and behavior, situated between the simpler processes of reflexes and homeostatic regulation⁶ and the more complex processes of cognition and deliberate action. Emotions are more flexible and context-dependent than reflexes but less so than deliberate behaviors.⁷ They can be viewed as having evolved to produce appropriate responses to environmental and internal challenges that are too variable for reflexes but do not require the full flexibility of cognition.

Humans can regulate emotions through mechanisms like facial expressions, allowing some control over both the feeling and expression of emotions. Non-human animals, however, typically display “honest” signals of their emotional states due to a lack of such control.⁸

Where in the brain do they come from?

Fear is probably the emotion whose neurobiology is best understood. It is closely tied to the amygdala, in both animals and humans. In Part 4, we will explore the complicated and indirect relationship between the amygdala and the conscious feeling of fear.⁹

Emotional processing relies on a wide network of brain regions, including the brainstem, hypothalamus, thalamus, amygdala, hippocampus, basal ganglia, anterior cingulate, insula, parietal cortex, and various subregions of the prefrontal cortex. Footnote 10 summarizes the roles played by each of these regions. It should be noted that there does not appear to be any single brain structure that participates in only one emotion. The important and interesting role of the prefrontal cortex in conscious feelings will be further discussed in Part 4.

Why it matters

Emotions influence nearly every aspect of our lives, from personal relationships and mental health to work performance and overall well-being. Understanding how they work is central to decoding the fundamental processes that drive human behavior, decision-making, and social interactions, and for comprehending and treating psychiatric disorders in patients like Amy and countless others who struggle in various ways to control their emotions.

Furthermore, understanding emotions is key to the mystery of consciousness.