Kaplan and Sadock’s Synopsis of Psychiatry: Behavioral Sciences/Clinical Psychiatry Eleventh Edition
The human brain is responsible for our cognitive processes, emotions, and behaviors— that is, everything we think, feel, and do. Although the early development and adult function of the brain are shaped by multiple factors (e.g., epigenetic, environmental, and psychosocial experiences), the brain is the final integrator of these influences. Despite the many advances in neural sciences over the last several decades, including the “decade of the brain” in the 1990s, and the wide acceptance of the brain as the biological substrate for normal and abnormal mental functions, there has not been a true transformational advance in the treatment of mental disorders for more than half a century. The most obvious reason for the absence of more progress is the profound complexity of the human brain. A perhaps less obvious reason is the current practice of psychiatric diagnosis, which, for most clinicians, is based on syndrome-based classification systems.
The purpose of this chapter is to introduce the neural sciences sections, which describe the anatomy and function of the human brain, and then to discuss how an evolution of thinking toward a brain-based or biologically based diagnostic system for mental illness might facilitate our efforts to advance brain research, to develop better treatments, and to improve patient care.
In other fields of medicine, diagnosis is based on physical signs and symptoms, a medical history, and results of laboratory and radiological tests. In psychiatry, a diagnosis is based primarily on the clinician’s impression of the patient’s interpretation of his or her thoughts and feelings. The patient’s symptoms are then cross-referenced to a diagnostic or classification manual (e.g., Diagnostic and Statistical Manual of Mental Disorders [DSM-5], International Statistical Classification of Diseases and Related Health Problems [ICD]) containing hundreds of potential syndromes, and one or more diagnoses are applied to the particular patient. These standard classification systems represent significant improvements in reliability over previous diagnostic systems, but there is little reason to believe that these diagnostic categories are valid, in the sense that they represent discrete, biologically distinct entities. Although a patient with no symptoms or complaints can be diagnosed as having diabetes, cancer, or hypertension on the basis of blood tests, X-rays, or vital signs, a patient with no symptoms cannot be diagnosed with schizophrenia, for example, because there are no currently recognized objective, independent assessments.
The goals of clinicians and researchers are to reduce human suffering by increasing our understanding of diseases, developing new treatments to prevent or cure diseases,and caring for patients in an optimal manner. If the brain is the organ of focus for mental illnesses, then it may be time to be more ambitious in building the classification of patients with mental illnesses directly from our understanding of biology, rather than only from the assessment of a patient’s symptoms.
THE HUMAN BRAIN
The following neural sciences sections each address a field of brain biology. Each of these fields could be relevant to the pathophysiology and treatment of mental illnesses. Although the complexity of the human brain is daunting compared with other organs of the body, progress can only be made if one approaches this complexity consistently, methodically, and bravely.
The neuronal and glial cells of the human brain are organized in a characteristic manner, which has been increasingly clarified through modern neuroanatomical techniques. In addition, our knowledge of normal human brain development has become more robust in the last decade. The human brain clearly evolved from the brain of lower animal species, allowing inferences to be made about the human brain from animal studies. Neurons communicate with one another through chemical and electrical neurotransmission. The major neurotransmitters are the monoamines, amino acids, and neuropeptides. Other chemical messengers include neurotrophic factors and an array of other molecules, such as nitric oxide. Electrical neurotransmission occurs through a wide range of ion channels. Chemical and electrical signals received by a neuron subsequently initiate various molecular pathways within other neurons that regulate the biology and function of individual neurons, including the expression of individual genes and the production of proteins.
In addition to the central nervous system (CNS), the human body contains two other systems that have complex, internal communicative networks: the endocrine system and the immune system. The recognition that these three systems communicate with each other has given birth to the fields of psychoneuroendocrinology and psychoneuroimmunology. Another property shared by the CNS, the endocrine system, and the immune system is the regular changes they undergo with the passage of time (e.g., daily, monthly), which is the basis of the field of chronobiology.
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