One of the most fundamental questions in cognitive neuroscience relates to the biological basis of functional hemispheric specialization and the relationship of structure to function. These important and controversial concepts are reviewed in The Asymmetrical Brain. Drs. Hugdahl and Davidson have selected core topics discussed by an impressive group of internationally recognized experts. This text was originally conceived as an update to the 1995 book Brain Asymmetry edited by Hugdahl and Davidson, but this text offers a completely reorganized approach to the topic that is both timely and comprehensive within a narrow focus on specific neural systems and neural syndromes. This book will appeal to students and experts in the broader field of human cognitive neuroscience and should be required reading to anyone with an academic interest in cerebral laterality and human cognition. Indeed, the field has advanced since 1995, and this book will surely become a major impetus to future research advancement in brain laterality.

This book has a total of 21 chapters contributed by 40 authors from six countries. These chapters are divided into seven sections that together provide a comprehensive exploration of a variety of complementary topics in cerebral laterality. The sections are: Section I–Animal Models/Basic Function, Section II–Neuroimaging and Brain Stimulation, Section III–Visual Laterality, Section IV–Auditory Laterality, Section V–Emotional Laterality, Section VI–Neurological Disorders, Section VII–Psychiatric Disorders. The first two sections include chapters that review background concepts (e.g., visual systems in birds–Chapter 1, determinants of hand preference–Chapter 4) and methodologies (neuroimaging and cortical stimulation) used to study brain asymmetry. The next three sections are devoted to specific neural systems (visual, auditory, and emotional processing). The final two sections shift to neurological and psychiatric disorders. The content of these individual sections will be briefly discussed below.

The first section, Animal Models and Basic Functions, presents background theoretical and conceptual models from animal and human studies. The chapters in this section review important core topics, and present some newer evolving concepts that are likely to facilitate future empiric studies. The first chapter is a very stimulating and comprehensive discussion of avian visual laterality by Onur Güntürkün who systematically demonstrates that animal models can inform about human laterality. Avian visual asymmetries develop within a critical period due to interplay of genetic and epigenetic factors that impact ascending visual pathways that become wired in a lateralized manner. The first section also includes a very interesting chapter by Akaysha Tang that presents a hippocampal theory of cerebral lateralization that is largely based on animal experiments that support the notion that brain asymmetry may be linked to experience-dependent mediation of anatomy and neurochemistry (Chapter 2). The asymmetry of dopamine efferents within prefrontal cortex is discussed in Chapter 3 with reference to stress and anxiety. Basic anatomy of these prefrontal circuits is reviewed with an emphasis on the interaction of prefrontal circuits with the hypothalamic-pituitary-adrenal axis and the amygdala. Finally, Chapter 4, by Alan Beaton, is a comprehensive review of our current understanding of the nature and heritability of handedness. Dr. Beaton discusses theories of handedness with an historical perspective that is advanced by his presentation of older and newer models including the testosterone model, the developmental instability model, and the role of learning. All of these chapters stand alone, but are woven together in a way that provides the reader with an idea of the complex interplay of many factors that ultimately effect human laterality and result in the range of individual differences in human behavior.

The second section of The Asymmetric Brain provides an overview of the contributions of neuroimaging and brain stimulation studies to our understanding of brain laterality. Tremendous progress has been made in the past thirty years with the greatest advances attributable to the technology which allows us to visualize the human brain in vivo. The merging of technology with computer-based imaging techniques has rapidly moved the field of neuroscience forward in the past thirty years. Imaging techniques include the study of cellular and subcellular elements in vitro to optical imaging of neuronal activity to imaging the whole brain in humans and nonhuman primates during cognitive operations. Cognitive neuroscience research is being driven by dramatic advances in neuroimaging methods, including structural and functional magnetic resonance imaging (MRI), and positron emission technology (PET). Structural details of the brain can be reconstructed using non-invasive methods (structural magnetic resonance imaging-MRI). Cognitive functions, such as learning and memory, language, attention and emotion, can be studied by analyzing subtle, task-related changes in cerebral blood flow (functional MRI). The timing of neural activity can be studied using cortical event related potentials (ERPs). It is important to examine the application of these advanced techniques to our understanding of human cerebral laterality. This section includes chapters that characterize functional asymmetries with brain mapping (Chapter 5), anatomical brain asymmetries with an emphasis on human brain structure and function (Chapter 6), and transcranial magnetic stimulation studies of asymmetrical cognitive functional reactivity in the human brain (Chapter 7).

The next three sections in the book shift the emphasis to specific neural systems including: Visual laterality (Section III), Auditory laterality (Section IV), and Emotional laterality (Section V). Section three explores visual laterality in three chapters that probe interhemispheric interactions and processing capacity (Chapter 8), spatial relations (Chapter 9), and issues of hemispheric transfer in sensorimotor tasks based on ERP studies. Section four examines auditory laterality in three chapters including the processing of tonal stimuli (Chapter 11), dichotic listening studies (Chapter 12), and the effects of attention (Chapter 13). Section five reviews emotional processing and laterality in three chapters that discuss cortical and subcortical circuitry (Chapter 14), regional brain activity in anxiety and depression (Chapter 15), and the state and trait nature of frontal electroenchalographic (EEG) asymmetry in emotional processing (Chapter 16). Once again each of these chapters stands alone, but taken together the information provided in these sections gives the reader a comprehensive overview of the complex nature of these neural systems and the pertinent issues of cerebral laterality in visual, auditory, and emotional processing.

Finally, the last two sections of the book shift to discussions of specific neurological (Section VI) and psychiatric (Section VII) disorders. In the section on neurological disorders, cognitive and sensorimotor deficits and compensatory strategies associated with agenesis of the corpus callosum are discussed in Chapter 17. Dyslexia is the basis of discussions in Chapters 18 and 19. The former chapter reviews neuroanatomical studies that purport that dyslexia may be associated with a variety of neural risk factors, and the latter chapter further elaborates on the discussion of some of these brain asymmetries in left-handers and in individuals with dyslexia. The section on psychiatric disorders includes two chapters. The first chapter discusses behavioral, physiological and neuroimaging findings in depressive disorders (Chapter 20). The final chapter presents a view of laterality issues in schizophrenia (Chapter 21).

In summary, The Asymmetric Brain is an outstanding contribution to the field of human brain anatomy and function. This rapidly evolving field of cognitive neuroscience is covered in a focused and comprehensive way in this edited text. Clinicians, educators and researchers in the field of human cognition and cerebral laterality look forward to future advances that will allow the more precise mapping of cognitive, emotional and sensorimotor systems onto the landscape of the human brain. Fields such as molecular imaging and gene therapy represent only two evolving fields that will allow us to advance our understanding of the brain and behavior. Researchers need to directly probe the potentially important relationships between brain morphology, behavior, and genetic susceptibility to neural syndromes that may converge on some cognitive, behavioral, neuroanatomical and neurophysiological measures and diverge on others. We look forward to advances in the field and to other volumes that discuss the basic issues that result in brain asymmetries.