Chapter 1. Neurobiological Bases of Cognition, Emotion, and Behavior

Field: Neuroscience (Life Sciences)

That brain and behavior are inseparable and that mental events are brain events are the physicalist philosophical foundations of neuropsychiatry (Arciniegas et al. 2006). Biological, social, and environmental factors, as well as their reciprocal interactions, are appreciated as influences on brain function in health and disease, and neuropsychiatrists recognize all of these factors as necessary elements of any account of mental (i.e., neuropsychiatric) function. Their influences on cognition, emotion, and behavior and the combined mechanisms by which they engender neuropsychiatric disorders, however, are understood and described in terms of their effects on brain structure and function. The Joint Advisory Committee on Subspecialty Certification of the American Neuropsychiatric Association and the Society for Behavioral and Cognitive Neurology (Arciniegas et al. 2006) directs subspecialists in Behavioral Neurology & Neuropsychiatry (BNNP) to elicit and construct comprehensive patient histories that emphasize neurodevelopmental and environmental influences on cognition, emotion, behavior, and elementary neurological function. Clinical assessment of these neuropsychiatric functions requires that practitioners understand brain-behavior relationships and possess the assessment skills needed to apply that understanding in clinical practice. The clinical assessment in BNNP employs, and is made systematic by, the use and interpretation of standardized, validated, and reliable metrics of neuropsychiatric function. Neuropsychological testing, neuroimaging, and electrophysiological and other laboratory measures that clarify the structural and functional neuroanatomy of illness, refine differential diagnostic considerations, and inform prognosis, treatment selection, and treatment response expectations are also employed, where appropriate (see Chapters 2 through 5). Interpreting clinical signs, symptoms, and syndromes in relation to structural and functional neuroanatomy (i.e., the neurobiological bases of behavior) therefore supersedes conventional (i.e., Diagnostic and Statistical Manual of Mental Disorders [DSM]–based) psychiatric diagnoses. This neuropsychiatric approach to clinical assessment and treatment is designed to avoid the practice of "mindless neurology" and "brainless psychiatry" that was pervasive during much of the twentieth century (Abraham 1999). It also eschews the historical dichotomization of clinical conditions into strict "psychiatric" or "neurological" types in favor of a more integrative approach. A comprehensive account of neuropsychiatric health and disease therefore demands a detailed understanding of the neurobiological bases of cognition, emotion, and behavior. A life span, or neurodevelopmental, perspective adds another dimension to understanding behavior: brain structure and function change dramatically with age—from fetal development through infancy, childhood, adolescence, adulthood, and old age. Physiological functions vary more widely in elderly people than in young people, tolerance of injury and potential for recovery are diminished in elderly patients, and the neurobehavioral consequences of brain dysfunction often differ as a function of the age of the patient. This chapter is intended to introduce readers of this volume to the neuroanatomical and neurochemical bases of cognition, emotion, and behavior. First, we present a synoptic model of behavioral neuroanatomy as a framework for the remaining discussion. The model divides the nervous system into three behaviorally relevant zones: an inner zone surrounding the ventricular system, a middle zone encompassing the basal ganglia and limbic system, and an outer zone composed primarily of the neocortex. We present the anatomy of each zone and describe the behavioral consequences of injury to each. Next, we describe two distributed systems; these cross the three zones to allow information to enter the brain (thalamocortical system) and allow impulses mediating action to exit the brain (frontal-subcortical circuits). We also present neuropsychiatric syndromes associated with abnormalities of these systems. Finally, we integrate the biochemical bases of neuropsychiatric function with structural and functional neuroanatomy. Readers seeking complementary and comprehensive syntheses of this information intended specifically for subspecialists in BNNP are referred to recent reviews (Arciniegas et al. 2013; Hart 2016).