**Abstract**

Emotions are automatic and primary patterns of purposeful cognitive-behavioral organizations. They have three main functions: coordination, signaling, and information. First, emotions coordinate organs and tissues, thus predisposing the body to peculiar responses. Scholars have not reached a consensus on the plausibility of emotion-specific response patterns yet. Despite the limitations, data support the hypothesis of specific response patterns for distinct subtypes of emotions. Second, emotional episodes signal the current state of the individual. Humans display their state with verbal behaviors, nonverbal actions (e.g., facial movements), and neurovegetative signals. Third, emotions inform the brain for interpretative and evaluative purposes. Emotional experiences include mental representations of arousal, relations, and situations. Every emotional episode begins with exposure to stimuli with distinctive features (i.e., elicitor). These inputs can arise from learning, expressions, empathy, and be inherited, or rely on limited aspects of the environment (i.e., sign stimuli). The existence of the latter ones in humans is unclear; however, emotions influence several processes, such as perception, attention, learning, memory, decision-making, attitudes, and mental schemes. Overall, the literature suggests the nonlinearity of the emotional process. Each section outlines the neurophysiological basis of elements of emotion.

**Keywords:** emotion, emotion definition, emotion faces, facial expressions, emotional experience, elicitor, sign stimuli, reward system, James-Lange theory, Cannon-Bard theory

## **1. Introduction**

The study of emotions has fascinated scholars from all over the world for millennia. Socrates and Plato dealt with it about two thousand five hundred years ago, and they probably were not even the first [1]. Although there have been considerable advances since then, our knowledge is far from complete.

In this chapter, the term *emotion* refers to "automatic and primary patterns of purposeful cognitive-behavioral organizations" [2]. Although there is no consensus, data suggest that emotions are "automatic models" since each subtype probably has specific neurophysiological layouts [3]. Furthermore, every emotional process is "primary" because, in certain situations, it coordinates the activity of the nervous system (e.g., perception, attention, and memory) [4]. The expression "cognitive-behavioral organizations" describes the coordinating nature of emotion and its ability to facilitate distinctive behavioral responses [5], while maintaining central control. In particular,

brain processing makes it possible to learn (see Section 5.1), inhibit, and regulate emotional responses [6]. Emotions are then "purposeful" because they aim to prepare the body to respond to situations that have occurred repeatedly throughout evolution [4].

On the whole, these features reveal the essential functions of emotions, namely [7]:


## **2. Coordination**

One of the first scientists to define the nature of emotions was probably William James. Until then, the prevalent idea was that situations evoke emotions that, in turn, trigger bodily changes. James instead claimed that "bodily changes follow directly the PERCEPTION of the exciting fact, and that our feeling of the same changes as they occur IS the emotion" (pp. 189–190) [8]. The Danish psychologist Lange developed similar concepts in the same period. Therefore, today, scholars refer to this idea as the *James-Lange theory*. Sensory systems send data about the current situation to the central nervous system. Subsequently, the CNS induces physiological changes (e.g., heartbeat and muscle tone). The following feeling of these changes is the emotion. In other words, there is no emotion without physiological changes. It seemed a counterintuitive thesis even then. Nevertheless, several scholars accepted the James-Lange theory [9].

Some years later, Walter Bradford Cannon falsified James's idea. He considered that stopping sensory sensitivity would impair the central perception of physiological changes, thereby eliminating emotions. Thus, Cannon resected the animals'spinal cords. Results suggested that surgically operated individuals still felt emotions, though. Furthermore, it seemed the same physiological changes accompanied various emotions. Cannon concluded that emotions disturb the activity of the autonomic nervous system (ANS) [10], and Philip Bard enriched this view. In brief, this hypothesis (i.e., the *Cannon-Bard theory*) [9] is an "all-or-none" approach with only two autonomic patterns: *non-activated* versus *diffusely activated* [5].

Neither theory has disappeared over the years. Indeed, they have led to two contrasting approaches.

First, nonstate theories and general arousal models suggest the inexistence of specific internal states of emotions [11]. The two-factor theory [12], the component process model [13], and other hypotheses [14] reach the same conclusion. Empirical evidence does not support the idea that emotions have specific ANS patterns. Part of the data instead suggests that undifferentiated arousal accompanies emotional experiences [3]. Something in the body happens, but are the people who label it as an emotional experience (e.g., fear, joy, and sadness) [15]. Therefore,

proponents of these theories (i.e., cognitive models) claim that emotions result from brain activity [5].

The second approach supports the existence of discrete emotions, each one characterized by specific neurophysiological and behavioral routines. In this case, scholars usually view emotions as an adaptive mechanism, a product of evolution [4]. Charles Darwin was probably the first to search for the cause of expressions [16]. Subsequently, several scientists focused on the link between emotions, autonomic activity, and behavioral responses (e.g., facial expressions) [17]. Proponents of this functionalevolutionary approach claim the existence of different emotions associated with biobehavioral layouts [5].

There is a lively debate still today. In particular, scholars did not reach a consensus on the existence of emotion-specific response patterns. One explanation for this diatribe lies in the methodological challenges the study of emotions entails. Individual differences (e.g., emotion recognition skills), the choice of elicitor (e.g., there is no certainty that a given stimulus elicits a given emotion in people), indicators (e.g., a continuous recording of different physiological and behavioral measures) [5], and statistical methods are among these [18].

Despite the issues, data support the hypothesis of specific response patterns for distinct subtypes of emotions [3]. For example, in rodents, different types of fear correspond to independent neural substrates [19]. Indeed, emotional families are sets of states that share elicitors (see Section 5), autonomic patterns, expressions, and behavioral reactions [17]. The neural substrates of emotional subtypes facilitate different behavioral responses. As an illustration, consider the *Fight Flight Freeze System* [20]:

