The emotional brain: Fundamental questions and strategies for future research

Attraction is altered via modulation of the medial prefrontal cortex without explicit knowledge

Previous studies have demonstrated that brain stimulation can alter an individual's physical appearance via dysregulation of the medial prefrontal cortex (MPFC). In this study, we attempted to determine if individuals who receive repetitive transcranial magnetic stimulation (rTMS) delivered to the MPFC were rated as more attractive by others. It has been previously reported that 1 hertz (Hz) (inhibitory) TMS can alter one's facial expressions such that frontal cortex inhibition can increase expressiveness. These alterations, detected by external observation, remain below the level of awareness of the subject itself. In Phase I, subjects (N = 10) received MPFC rTMS and had their photographs taken after each of the five stimulation conditions, in addition to making self-ratings across a number of variables, including attractiveness. In Phase II, participants (N = 430) rated five pictures of each of the Phase 1 individuals on attractiveness. It was found that there were no significant differences in self-assessment following rTMS (Phase I). However, attractiveness ratings differed significantly in Phase II. There was a significant difference found between 10 Hz TMS delivered to the MPFC (p < 0.001), such that individuals were rated as less attractive. Furthermore, 1 Hz TMS to the MPFC increased the number of 'Most Attractive' ratings, while 10Hz TMS decreased the number of 'Most Attractive' ratings (p < 0.001). These results suggest that the MPFC plays a role in attractiveness ratings to others. These data also support research showing that one's appearance can be altered below the level of awareness via rTMS. To our knowledge, this is the first investigation to examine how brain stimulation influences one's attractiveness.

Pain perception as hierarchical Bayesian inference: A test case for the theory of constructed emotion

An intriguing perspective about human emotion, the theory of constructed emotion considers emotions as generative models according to the Bayesian brain hypothesis. This theory brings fresh insight to existing findings, but its complexity renders it challenging to test experimentally. We argue that laboratory studies of pain could support the theory because although some may not consider pain to be a genuine emotion, the theory must at minimum be able to explain pain perception and its dysfunction in pathology. We review emerging evidence that bear on this question. We cover behavioral and neural laboratory findings, computational models, placebo hyperalgesia, and chronic pain. We conclude that there is substantial evidence for a predictive processing account of painful experience, paving the way for a better understanding of neuronal and computational mechanisms of other emotions.

Facial expression and emotion

Human facial expressions are unique in their ability to express our emotions and communicate them to others. The mimic expression of basic emotions is very similar across different cultures and has also many features in common with other mammals. This suggests a common genetic origin of the association between facial expressions and emotion. However, recent studies also show cultural influences and differences. The recognition of emotions from facial expressions, as well as the process of expressing one's emotions facially, occurs within an extremely complex cerebral network. Due to the complexity of the cerebral processing system, there are a variety of neurological and psychiatric disorders that can significantly disrupt the coupling of facial expressions and emotions. Wearing masks also limits our ability to convey and recognize emotions through facial expressions. Through facial expressions, however, not only "real" emotions can be expressed, but also acted ones. Thus, facial expressions open up the possibility of faking socially desired expressions and also of consciously faking emotions. However, these pretenses are mostly imperfect and can be accompanied by short-term facial movements that indicate the emotions that are actually present (microexpressions). These microexpressions are of very short duration and often barely perceptible by humans, but they are the ideal application area for computer-aided analysis. This automatic identification of microexpressions has not only received scientific attention in recent years, but its use is also being tested in security-related areas. This article summarizes the current state of knowledge of facial expressions and emotions.

The role of affect in chronic pain: A systematic review of within-person symptom dynamics

OBJECTIVE

Chronic pain is conceptualized as a biopsychosocial phenomenon that involves both physical and emotional processes. The vast majority of research regarding these facets of chronic pain characterizes differences between individuals. In this review, we describe problems with assuming that differences between persons accurately characterize within-person processes. We also provide a systematic review of studies that have examined within-person relationships between pain and affect among individuals with chronic pain.

METHOD

Articles published by December 2020 that pertained to within-person assessment of pain and emotion, affect, or mood were identified. Data regarding study design, adherence, and concurrent and prospective relationships among pain and affect variables were extracted and summarized.

RESULTS

Of 611 abstracts, 55 studies met inclusion criteria. Results suggest that individuals with chronic pain tend to experience increased negative affect and decreased positive affect when experiencing more severe pain (r_pooled = .18 and - .19, respectively). However, the size of these effects appeared smaller than between-person associations, and there was evidence of significant variability between individuals. Examination of predictive relationships between pain and affect largely suggested the tendency of symptoms to predict themselves, rather than pain predicting affect or vice versa.

CONCLUSIONS

Consistent with group-level relationships, experiencing more severe pain relative to an individual's average seems to be associated with more negative affect and less positive affect. However, individuals vary in the size and even direction of these effects. More research is necessary to understand the implications of such variability for the assessment and treatment of chronic pain.

Expressions of emotions across species

What are emotions and how should we study them? These questions give rise to ongoing controversy amongst scientists in the fields of neuroscience, psychology and philosophy, and have resulted in different views on emotions [1-6]. In this review, we define emotions as functional states that bear essential roles in promoting survival and thus have emerged through evolution. Emotions trigger behavioral, somatic, hormonal, and neurochemical reactions, referred to as expressions of emotion. We discuss recent studies on emotion expression across species and highlight emerging common principles. We argue that detailed and multidimensional analyses of emotion expressions are key to develop biology-based definitions of emotions and to reveal their neuronal underpinnings.

Expression Authenticity: The Role of Genuine and Deliberate Displays in Emotion Perception

People dedicate significant attention to others' facial expressions and to deciphering their meaning. Hence, knowing whether such expressions are genuine or deliberate is important. Early research proposed that authenticity could be discerned based on reliable facial muscle activations unique to genuine emotional experiences that are impossible to produce voluntarily. With an increasing body of research, such claims may no longer hold up to empirical scrutiny. In this article, expression authenticity is considered within the context of senders' ability to produce convincing facial displays that resemble genuine affect and human decoders' judgments of expression authenticity. This includes a discussion of spontaneous vs. posed expressions, as well as appearance- vs. elicitation-based approaches for defining emotion recognition accuracy. We further expand on the functional role of facial displays as neurophysiological states and communicative signals, thereby drawing upon the encoding-decoding and affect-induction perspectives of emotion expressions. Theoretical and methodological issues are addressed with the aim to instigate greater conceptual and operational clarity in future investigations of expression authenticity.

What Is the Relationship between Pain and Emotion? Bridging Constructs and Communities

Although pain is defined as a sensory and emotional experience, it is traditionally researched and clinically treated separately from emotion. Conceptual and mechanistic relationships between these constructs highlight the need for better understanding of their bi-directional influences and the value of bridging the pain and emotion research and clinical communities.

Identifying the representational structure of affect using fMRI

The events we experience day to day can be described in terms of their affective quality: some are rewarding, others are upsetting, and still others are inconsequential. These natural distinctions reflect an underlying representational structure used to classify affective quality. In affective psychology, many experiments model this representational structure with two dimensions, using either the dimensions of valence and arousal, or alternatively, the dimensions of positivity and negativity. Using fMRI, we show that it is optimal to use all four dimensions to examine the data. Our findings include (1) a gradient representation of valence that is anatomically organized along the fusiform gyrus and (2) distinct sub-regions within bilateral amygdala that track arousal versus negativity. Importantly, these results would have remained concealed had either of the commonly used 2-dimensional approaches been adopted a priori, demonstrating the utility of our approach.

Altered corticolimbic connectivity reveals sex-specific adolescent outcomes in a rat model of early life adversity

Exposure to early-life adversity (ELA) increases the risk for psychopathologies associated with amygdala-prefrontal cortex (PFC) circuits. While sex differences in vulnerability have been identified with a clear need for individualized intervention strategies, the neurobiological substrates of ELA-attributable differences remain unknown due to a paucity of translational investigations taking both development and sex into account. Male and female rats exposed to maternal separation ELA were analyzed with anterograde tracing from basolateral amygdala (BLA) to PFC to identify sex-specific innervation trajectories through juvenility (PD28) and adolescence (PD38;PD48). Resting-state functional connectivity (rsFC) was assessed longitudinally (PD28;PD48) in a separate cohort. All measures were related to anxiety-like behavior. ELA-exposed rats showed precocial maturation of BLA-PFC innervation, with females affected earlier than males. ELA also disrupted maturation of female rsFC, with enduring relationships between rsFC and anxiety-like behavior. This study is the first providing both anatomical and functional evidence for sex- and experience-dependent corticolimbic development.

Having a traumatic childhood increases the risk a person will develop anxiety disorders later in life. Early life adversity affects men and women differently, but scientists do not yet know why. Learning more could help scientists develop better ways to prevent or treat anxiety disorders in men and women who experienced childhood trauma.

Anxiety occurs when threat-detecting brain circuits turn on. These circuits begin working in infancy, and during childhood and adolescence, experiences shape the brain to hone the body’s responses to perceived threats. Two areas of the brain that are important hubs for anxiety-related brain circuits include the basolateral amygdala (BLA) and the prefrontal cortex (PFC).

Now, Honeycutt et al. show that rats that experience early life adversity develop stronger connections between the BLA and PFC, and these changes occur earlier in female rats. In the experiments, one group of rats was repeatedly separated from their mothers and littermates (an early life trauma), while a second group was not. Honeycutt et al. examined the connections between the BLA and PFC in the two groups at three different time periods during their development: the juvenile stage, early adolescence, and late adolescence.

The experiments showed stronger connections between the BLA and PFC begin to appear earlier in juvenile traumatized female rats. But these changes did not appear in their male counterparts until adolescence. Lastly, the rats that developed these strengthened BLA-PFC connections also behaved more anxiously later in life. This may mean that the ideal timing for interventions may be different for males and females. More work is needed to see if these results translate to humans and then to find the best times and methods to help people who experienced childhood trauma.

Dispositional negativity, cognition, and anxiety disorders: An integrative translational neuroscience framework

When extreme, anxiety can become debilitating. Anxiety disorders, which often first emerge early in development, are common and challenging to treat, yet the underlying mechanisms have only recently begun to come into focus. Here, we review new insights into the nature and biological bases of dispositional negativity, a fundamental dimension of childhood temperament and adult personality and a prominent risk factor for the development of pediatric and adult anxiety disorders. Converging lines of epidemiological, neurobiological, and mechanistic evidence suggest that dispositional negativity increases the likelihood of psychopathology via specific neurocognitive mechanisms, including attentional biases to threat and deficits in executive control. Collectively, these observations provide an integrative translational framework for understanding the development and maintenance of anxiety disorders in adults and youth and set the stage for developing improved intervention strategies.

Implicit measurement of emotional experience and its dynamics

Although many studies revealed that emotions and their dynamics have a profound impact on cognition and behavior, it has proven difficult to unobtrusively measure emotions. In the current study, our objective was to distinguish different experiences elicited by audiovisual stimuli designed to evoke particularly happy, sad, fear and disgust emotions, using electroencephalography (EEG) and a multivariate approach. We show that we were able to classify these emotional experiences well above chance level. Importantly, we retained all the information (frequency and topography) present in the data. This allowed us to interpret the differences between emotional experiences in terms of component psychological processes such as attention and arousal that are known to be associated with the observed activation patterns. In addition, we illustrate how this method of classifying emotional experiences can be applied on a moment-by-moment basis in order to track dynamic changes in the emotional response over time. The application of our approach may be of value in many contexts in which the experience of a given stimulus or situation changes over time, ranging from clinical to consumption settings.