The Human Amygdala (edited by Paul J. Whalen and Elizabeth A. Phelps) presents up-to-date information about the structure and function of the human amygdala. In recent years, there has been a large increase in our knowledge of the role of the human amygdala in normal and abnormal emotional/behavioral functions due, in part, to technological advances like human neuroimaging that have built on the findings from pioneering basic animal research. This book consists of 18 chapters on various aspects of the amygdala written by leading researchers in the field. This volume is a valuable resource for updating one's knowledge regarding the important role the amygdala and its subdivisions play in normal and abnormal emotional functioning.
This volume is composed of three sections. Part I (“From Animal Models to Human Amygdala Function”) consists of four chapters (∼25% of the book). The first chapter provides a detailed account of the neuroanatomy of the primate amygdala including its intrinsic and extrinsic connections. The human amygdala (or perhaps more aptly referred to as the amygdaloid complex) is a relatively small but complex brain structure consisting of a heterogeneous group of 13 interconnected nuclei and cortical areas found just rostral to the hippocampus in the medial temporal lobe. The amygdala has reciprocal connections with numerous cortical and subcortical structures. The amygdala receives information from all sensory modalities and also receives information about the animal's internal state, integrates the information, and then projects back to multiple brain areas exerting an “emotional influence” over behavior. The remaining chapters in this section discuss insights into the human amygdala from animal studies such as the role of the amygdala in associative learning including fear conditioning, extinction, and positive reinforcement.
Part II (“Human Amygdala Function”) discusses healthy human amygdala functions especially findings from studies using functional brain imaging. This section consists of nine chapters (∼50% of the book) including a developmental perspective of human amygdala functioning, methodological approaches to studying the human amygdala, individual differences in human amygdala function, and separate chapters on the role of the human amygdala in fear conditioning, emotional memory, the control of fear, perception and attention, and social functioning. Currently, the spatial resolution of human neuroimaging is limited, which affects our ability to study localization of function for different nuclei making up the amygdaloid complex in human studies. However, knowledge and hypotheses derived from animal studies regarding the functions of each of the nuclei of the amygdaloid complex will be increasingly important in guiding future human neuroimaging work when technological advances allow for higher spatial resolution.
Part III (“Human Amygdala Dysfunction”) consists of five chapters (25% of the book) and discusses human amygdala dysfunction in psychiatric/neurological disorders including anxiety disorders, schizophrenia, autism, normal aging, and Alzheimer's disease (AD). Emotional disorders like anxiety and depression appear to involve a breakdown in communication between the medial prefrontal cortex and the amygdala. After the entorhinal cortex and hippocampus, the amygdala is one of the first brain areas affected by AD pathology including in the MCI stage and likely plays a role in the neuropsychiatric symptoms of AD. There is also a chapter on the genetic basis of amygdala reactivity including the use of “genomic imaging” in the study of individual differences in amygdala function.
The book provides the reader with a better understanding of the complexity of the structure of the amygdaloid complex and its many cortical and subcortical connections. It provides the reader with an appreciation for the multiple ways that the amygdala, in health and disease, can affect emotional/behavioral functioning. The book presents evidence that a major role of the amygdala is in “salience detection” in addition to “danger detection” and fear learning. The amygdala is responsive to predictors of threat especially where there is predictive ambiguity or uncertainty, which triggers vigilance and further inquiry about the possible threat. However, the amygdala is maladaptively hyper-responsive in post traumatic stress disorder (PTSD). It remains to be determined if amygdala hyper-responsivity in PTSD is due to diminished top-down inhibition by the medial prefrontal cortex or due to increased bottom-up sensitivity of the amygdala. Data are also presented indicating that the amygdala plays an important role in some aspects of positive reinforcement in addition to its initially emphasized role in negative reinforcement. The amygdala also plays an essential role in learning associations between a stimulus and its emotional significance, that is, it assigns value to stimuli in certain circumstances. Because the amygdala is involved in attaching an emotional valence to stimuli, it affects where attention is directed and sustained and what is learned and remembered, which is a major way that the amygdala can affect cognitive functioning in everyday life.
What is the utility of this book for the clinical practice in neuropsychology? Neuropsychology is the study of brain-behavior relationships. A clinical neuropsychological evaluation should include a review of the emotional/motivational status of the patient and how it impacts the patient's everyday adaptive functioning including how it might negatively or positively affect everyday cognitive and academic functioning. Furthermore, it is important to determine if there might be a neurological basis to any changes in the emotional status of the patient. Knowledge of the brain basis of emotion including emotional influences on cognitive functioning and adaptive behavior is an essential area of expertise in clinical neuropsychology. Although the amygdala is not the “seat of emotion,” it appears to be a neural nexus point (i.e., a “Grand Central Station”) in an interconnected network of brain areas involved in many important aspects of emotional functioning. Because the amygdala plays an important role in various aspects of emotional functioning and because there is now a large and growing body of both animal and human research on amygdala-behavior relationships, “every neuropsychologist should be a student of the amygdala.” The breadth and depth of the research on the amygdala covered in this book by experts in the field makes it the best current reference on the human amygdala and an excellent way to stimulate thinking about the role emotion plays in human behavior including its effects on everyday cognitive functioning.