**5. Elicitors of emotions**

An emotional episode begins through exposure to stimuli with specific features. For example, loss causes sadness [50]. In this sense, emotion is a process, and these stimuli (i.e., *elicitors*) are the inputs that initiate it.

Animals learn to feel certain emotions in specific situations. However, it is not just environmental cues that trigger an emotional episode. The state of the organism, behavior, and other complex faculties (e.g., thoughts and empathy) can be elicitors too.

#### **5.1 Learning**

Stimuli internal and external to the body can become elicitors of emotion through classical and operant conditioning. In particular, animals learn to associate a stimulus (S) with a specific emotional response (R). With an S-R association established, exposure to S may be sufficient to elicit the emotional response.

Yet, S-R associations can take complex forms. For instance, emotional reactions can even be self-reinforcing. An individual may experience a pleasant state that elicits behavior, which fuels repetition in a sort of loop [51]. However, the S-R associability is not absolute. For example, it seems impossible to teach a hungry pigeon to fly away by presenting it with food [52].

At the basis of emotional learning is a vast neural network that includes the reward system. Its architecture is complex and involves circuits for the cost/benefit assessment of specific reward values, reward expectations, and action selection (**Figure 3**). The amygdaloid complex and ventral striatum (vStr) underpin the appetitive

#### **Figure 3.**

*Schematic representation of reward system. One: cost/benefit assessment of specific reward value. Two: cortical loop. Three: limbic loop. Four: reward expectation. Five: action selection. Six: go and stop processes. Abbreviations: Amg, Amygdaloid complex; DA, dopamine; dlPFC, dorsolateral prefrontal cortex; dStr, dorsal striatum; GP, globus pallidus; Hip, hippocampus; OFC, orbitofrontal cortex; SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata; STN, subthalamic nucleus; vStr, ventral striatum; VTA, ventral tegmental area. This article was published in [53] Copyright Elsevier (2020).*

processing of reward expectations. Moreover, dopamine (DA) pathways modulate motivation and behavior by connecting the ventral tegmental area, the substantia nigra pars compacta (SNc), and the striatum. The reward system is also capable of inhibiting the behavior. Specifically, five sub-circuits (or sub-loops) of the basal ganglia (BG) are essential for various functions, including action cancelation [53].

#### **5.2 Expressions**

Even emotional signals (see Section 3) can be elicitors. For example, breathing [54], vocalizations [55], and postures [56] may elicit emotions. Indeed, some experiments suggest that an expansive pose lowers cortisol and increases testosterone levels. That would be enough to produce feelings of power and increase risk tolerance [57]. However, attempts to replicate such data have failed [58].

In general, *peripheral feedback theories* propose the idea that emotional expressions can become elicitors [56]. For example, facial expressions could trigger emotions. According to this idea (i.e., the *facial feedback hypothesis*), movements of the face influence the release of some neurotransmitters, thus acting as an elicitor [59]. Therefore, feedback theories follow the path traced by the James-Lange theory (see Section 2).

Observing signals and behaviors in others can also initiate the emotional process. In this sense, indirect experience (e.g., imitation and emotional contagion) is a potential elicitor of emotion. The anterior insula and the rostral cingulate cortex are part of the neural network responsible for these mechanisms [60].

#### **5.3 Empathy**

Empathy consists of the emotional states produced by observation of individuals and situations. Thus, it is an elicitor of emotion *per se*. Scholars usually distinguish between *cognitive empathy* (CE) and *emotional empathy* (EE). The CE deals with mental perspective-taking, mentalizing, and the theory of mind. Instead, EE consists of the vicarious sharing of emotions [61].

The resulting emotion may be the same as that of the observed individual, but not necessarily. Indeed, the emotional experience can be so intense as to produce an *empathic overarousal*, which often induces disengagement [62]. That happens, for example, to paramedics who, being exposed to traumatic events, adopt coping strategies, such as emotional detachment [63]. In other cases, emotions felt may be diverse from those observed. That is the case of *Schadenfreude* (i.e., the pleasure caused by the misfortune of others) [64].

Given the complexity of empathy as a faculty, it seems clear that its neurobiological basis is equally complex. For example, its neural substrate includes the insula, cingulate cortex, and the interoceptive network [65]. Furthermore, empathic responses probably depend on various processes (e.g., emotional contagion and affective mentalizing) that underpin distinct neural mechanisms. The temporoparietal junction, medial temporal lobe, prefrontal cortex, and dopamine pathways are part of the circuits of cognitive empathy. Instead, the neural substrates of emotional empathy include the frontal gyrus, insula, anterior cingulated cortex, and oxytocin paths [66].

#### **5.4 Sign stimuli**

Animals can feel emotions even when exposed to stimuli they have never encountered. For instance, the smell of predators they have never seen before scares rats [67]. Some scholars claim that humans also have innate fears (e.g., snakes) [68]. However, experimental results are controversial [69].

Several animals can respond to limited aspects of the environment (i.e., *sign stimuli*), ignoring the rest [70]. The common toad (*Bufo bufo*) produces defensive responses (e.g., stiff-legged) when faced with relatively simple perceptual patterns (dummies) with specific configurational features reminiscent of their predators (i.e., snakes) [71]. Moreover, newborn babies prefer and imitate human face schematizations (i.e., *facelike patterns*) [72].

From a neurobiological point of view, it is unlikely that there are cells in the nervous system specialized in innately identifying specific stimuli. The determinants of any sign stimuli as elicitors could lie, then, in the biological predisposition [52].
