Book Review: The Neuroscience of Emotion: A New Synthesis

By Martina Nonni

Emotions are important aspects of our lives and everyday experiences. While scientists agree that they do exist, they don’t seem to agree on much else. Researchers are not sure about what they are, how they work, or if they are unique to humans. Since we all experience emotions, we all seem to think we know what they are, and we all have strong instinctive beliefs about them.

Do animals have emotions? Can we find simple emotions in insects and invertebrates? Can we identify different areas of the brain behind different emotions, or do they result from a global, network effort? Ask these questions to a group of researchers and surely you will leave with more questions than before and with few science-backed reasons for their beliefs.

As the topic of emotion attracts experts from many fields, including neuroscience, psychology, philosophy, computer science, and engineering, it’s not surprising that their approaches are also greatly different.


In The Neuroscience of Emotion: A New Synthesis, Ralph Adolphs and David J. Anderson argue that, for a complete science of emotion, we need to leave behind our instinctive assumptions and conclusions and approach this subject accurately and objectively. The authors, who are colleagues at the California Institute of Technology (Caltech), bring insight from different fields: while Adolphs researches social behavior and its neural basis in humans, Anderson studies how internal states result in emotional behavior in mice and flies. Their aim is not to share a comprehensive new theory of emotion, but, instead, to survey the field and to provide a framework for investigating emotions across species, techniques, and time.

But what do scientists refer to, precisely, when they talk about “emotions”? This seems to change depending on who you ask. As the topic of emotion attracts experts from many fields, including neuroscience, psychology, philosophy, computer science, and engineering, it’s not surprising that their approaches are also greatly different.

The authors begin by proposing a functional approach to understanding emotions: emotions, they say, should be defined by what they do (their function), rather than by what they are made of or by how they work. To understand Adolphs and Anderson’s idea, let’s consider a clock: If you asked someone to tell you what a clock is, they wouldn’t start by saying that a clock needs gears, a pendulum and at least one clock hand. Instead, what they might say is that a clock is a device that measures time. This is a functional definition.

From a functional point of view, emotions are brain states usually caused by stimuli or events that, in turn, induce behaviors and other changes we can measure. With this functional definition, we can ignore all complications linked to the everyday use of the word “emotion” and we can study those internal brain states without worrying whether animals do or do not have subjective feelings, or whether there are sets of “natural”, “basic” or “social” emotions. We can set these topics aside, at least for the moment, for purely practical reasons, because there is no agreement on how to approach them. In the case of feelings and conscious experience, we are not even sure how to measure them.

From a functional point of view, emotions are brain states usually caused by stimuli or events that, in turn, induce behaviors and other changes we can measure.

Historically, emotion research comes from studies on human and animal behavior: standardized laboratory tests and ethological observations in the wild for animals, and self-report studies in humans. Historically, before the advent of functional neuroimaging, human studies mainly consisted of case reports and research on brain lesions. Nowadays, the majority of neuroscience studies in humans (and a growing number in animals) use neuroimaging methods, primarily functional Magnetic Resonance Imaging (fMRI), Electroencephalography (EEG) and, more recently, Transcranial Magnetic Stimulation (TMS). In the past, the quality of fMRI studies was problematic, from statistical power issues to controversial analyses, but the field is evolving rapidly. Current studies have better sample sizes, more powerful scanners, and sophisticated analysis methods. Considering that it is a noninvasive method, the future of fMRI in emotion research looks safe and full of potential.

One of the great advantages of human studies is that humans can speak and communicate, which becomes important when looking into emotions and subjective experiences. Yet, human studies come with important differences in ethical and practical approaches. Studies in humans are overall easier to carry out, but the methods used are in many ways limited compared to those used in animal research. As participants, we don’t require long training periods before experiments, and the emotions that can be studied range from fear to satisfaction and from disgust to hope. However, the results give us a descriptive account of emotions as well as the brain regions that were active at that time, without insight on whether areas or networks are sufficient or necessary for the emotional experience. In animals studies, on the other hand, scientists can manipulate different neurons in the brain and even certain mechanisms at a cellular level. Optogenetic and pharmacogenetic methods allow us to activate or inhibit specific neurons at will (using light or drugs, respectively) in a freely moving animal. These approaches have revolutionized animal studies with their ability to infer causal relationships between different neurons in different brain areas.

One of the most important and imminent challenges for the future is to learn to relate animal and human studies. The authors stress that, to do this, we need interdisciplinary insight and close collaboration between the people who formulate the theories, and the people who do the research. Investigations in animals can guide us and tell us where to look and, together with human research, they should supplement each other rather than working in opposite, often unrelated directions.

Many studies in humans have jumped to researching complex human emotions like guilt, shame, pride and love, but scientists often overlook that what happens behind the scenes in our brain is already complex, and not entirely agreed upon. Some experts argue that to answer the question “What emotion am I experiencing right now?” our brain evaluates our motivations, our past experiences, our bodily response to the situation, and what we believe we should be feeling at the moment. Many theories (Multi-component theories of Emotions) agree that emotions result from the interaction of all these components, but others (Interoceptive theories) argue that the only prerequisite to experiencing emotions is the ability to perceive one’s body states, for example, increased heartbeat or respiration (see Moors, 2009 for a comprehensive review).

Adolphs and Anderson create an excellent, logically planned, current review of the field, including fundamental and recent discoveries alongside past and present techniques, to bring together the separate worlds of human and animal emotion research. Following their arguments requires attention and interest, and an educated reader will find their writing eloquent yet fluent, less demanding than a textbook, but too precise and detailed to be considered a popular science book.

The book finishes with a review of the many current theories of emotion. While there is no shortage of models and data on emotion, the authors warn that a universal “theory of emotion” might not be possible or even useful. We need theories to be more circumscribed, and we need theories that can be tested — either in animals or humans. We need to understand which results would support which model, and we need data that can help decide if a theory is right or wrong. If we are interested in the evolutionary origins of emotions, it doesn’t matter what we call those states, as long as we are specific about what we are looking for and have accurate and objective ways of measuring it.

The takeaway lesson that I will hold dearly is that progress can be made even without answering all the open questions. You can take a step forward and set aside the uncertainties at the same time.

Adolphs and Anderson wrote The Neuroscience of Emotion with this in mind, sharing their knowledge and advice in an extensive and insightful manual on the science of emotion, hoping to sketch a collaborative path for researchers interested in this complicated topic.

The takeaway lesson that I will hold dearly is that progress can be made even without answering all the open questions. You can take a step forward and set aside the uncertainties at the same time.

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Written by Martina Nonni
Illustrated by Nadia Penkofflidbeck
Edited by Mariella Careaga and Lauren Wagner

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References
Moors, A. (2009). Theories of emotion causation: A review. Cognition & Emotion, 23(4), 625–662. https://doi.org/10.1080/02699930802645739

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