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All these definition are based on APA Dictionary. We have selected some terms here and you may find more at


'an almond-shaped structure in the temporal lobe that is a component of the limbic system and considered part of the basal ganglia. It comprises two main groups of nuclei—the corticomedial group and the basolateral group—and through widespread connections with other brain areas has numerous viscerosensory and autonomic functions as well as an important role in memory, emotion, perception of threat, and fear learning. Also called amygdaloid body; amygdaloid complex; amygdaloid nuclei.' - APA

Art Therapy

'the use of artistic activities, such as painting and clay modeling, in psychotherapy and rehabilitation. The process of making art is seen as healing, an experience that provides the opportunity to express oneself imaginatively, authentically, and spontaneously; over time, this process can lead to personal fulfillment, emotional reparation, and transformation. The products made in art therapy are seen as a means of symbolic communication and a vehicle for developing new insights and understandings, resolving conflicts, solving problems, and formulating new perceptions to achieve positive changes, growth, and rehabilitation.' - APA


'in front of or toward the front. In reference to two-legged upright animals, this term is sometimes used interchangeably with ventral to mean toward the front surface of the body. ' - APA


'a chemical compound that contains one or more amino groups (–NH2). Several neurotransmitters are amines, including acetylcholine, norepinephrine, and serotonin.' - APA

Acute Stress Disorder

'a disabling psychological condition that can occur immediately after exposure to a traumatic stressor. Symptoms such as intrusive thoughts, hyperarousal, and avoidance of situations that recall the traumatic event are the same as those of posttraumatic stress disorder but do not last longer than 4 weeks. This disorder may also include elements of dissociation, such as depersonalization and derealization.' - APA

Abnormal Psychology

'the branch of psychology devoted to the study, assessment, treatment, and prevention of maladaptive behavior. ' - APA

Action Potential (AP)

'the change in electric potential that propagates along the axon of a neuron during the transmission of a nerve impulse or the contraction of a muscle. It is marked by a rapid, transient depolarization of the cell’s plasma membrane, from a resting potential of about –70 mV (inside negative) to about +30 mV (inside positive), and back again, after a slight hyperpolarization, to the resting potential. Each action potential takes just a few milliseconds. Also called spike potential.' -APA

Amino Acid

'an organic compound that contains an amino group (–NH2) and a carboxyl group (–COOH). Twenty amino acids are constituents of proteins; nine of these are essential amino acids, that is, they cannot be synthesized by the body and must be obtained from foods. Other amino acids (e.g., glutamic acid, glycine) are neurotransmitters or precursors to neurotransmitters.' - APA


'attention-deficit/hyperactivity disorder. a behavioral syndrome characterized by the persistent presence of six or more symptoms involving (a) inattention (e.g., failure to complete tasks or listen carefully, difficulty in concentrating, distractibility) or (b) impulsivity or hyperactivity (e.g., blurting out answers; impatience; restlessness; fidgeting; difficulty in organizing work, taking turns, or staying seated; excessive talking; running about; climbing on things). The symptoms, which impair social, academic, or occupational functioning, start to appear before the age of 7 and are observed in more than one setting. ADHD has been given a variety of names over the years, including the still commonly used attention-deficit disorder (ADD)' - APA

Avoidant Personality Disorder

'a personality disorder characterized by (a) hypersensitivity to rejection and criticism, (b) a desire for uncritical acceptance, (c) social withdrawal in spite of a desire for affection and acceptance, and (d) low self-esteem. This pattern is long-standing and severe enough to cause objective distress and seriously impair the ability to work and maintain relationships. It is included in both DSM–IV–TR and DSM–5. [first defined in 1969 by Theodore Millon]' - APA


'the long, thin, hollow, cylindrical extension of a neuron that normally carries a nerve impulse away from the cell body. An axon often branches extensively and may be surrounded by a protective myelin sheath. Each branch of an axon ends in a terminal button (also called synaptic bouton or knob, among numerous other synonyms) from which an impulse is transmitted, through discharge of a neurotransmitter, across a synapse to a neighboring neuron. Also called nerve fiber.' - APA

Arachnoid Matter

'the middle one of the three membranous layers (meninges) covering the surface of the brain and spinal cord, so called because its strands of tissue resemble spiders’ webs. Also called arachnoid; arachnoid membrane.' -APA

Acetylcholine (ACh)

'a major, predominantly excitatory but also inhibitory, neurotransmitter both in the central nervous system, where it plays an important role in memory formation and learning and is implicated in Alzheimer’s disease, and in the peripheral nervous system, where it mediates skeletal, cardiac, and smooth muscle contraction and is implicated in myasthenia gravis and other movement disorders.' - APA


'an emotion characterized by apprehension and somatic symptoms of tension in which an individual anticipates impending danger, catastrophe, or misfortune. The body often mobilizes itself to meet the perceived threat: Muscles become tense, breathing is faster, and the heart beats more rapidly. Anxiety may be distinguished from fear both conceptually and physiologically, although the two terms are often used interchangeably. Anxiety is considered a future-oriented, long-acting response broadly focused on a diffuse threat, whereas fear is an appropriate, present-oriented, and short-lived response to a clearly identifiable and specific threat.' - APA

Autonomic Nervous System (ANS)

'the portion of the nervous system innervating smooth muscle and glands, including the circulatory, digestive, respiratory, and reproductive organs. It is divided into the sympathetic nervous system and parasympathetic nervous system. Autonomic responses typically involve changes in involuntary bodily functions, such as heart rate, salivation, digestion, perspiration, pupil size, hormone secretion, bladder contraction, and engorgement of the penis and clitoris. The system is called autonomic because it was once thought to function independently of the central nervous system.' -APA


'in front of or toward the front. In reference to two-legged upright animals, this term is sometimes used interchangeably with ventral to mean toward the front surface of the body. ' - APA

Association Fiber

'an axon from any of various neurons that link different parts of the same cerebral hemisphere.' - APA

Autism Spectrum Disorder (ASD)

'any one of a group of disorders with an onset typically occurring during the preschool years and characterized by varying but often marked difficulties in communication and social interaction. ASD was formerly said to include such disorders as the prototype autism, Asperger’s disorder, childhood disintegrative disorder, and Rett syndrome; it was synonymous with pervasive developmental disorder but more commonly used, given its reflection of symptom overlap among the disorders. It is now the official term used in DSM–5, where it encompasses and subsumes these disorders: Autism, Asperger’s disorder, and childhood disintegrative disorder are no longer considered distinct diagnoses, and medical or genetic disorders that may be associated with ASD, such as Rett’s syndrome, are identified only as specifiers of the disorder. Also called autistic spectrum disorder.' - APA

Behavioral Psychology

'the branch of psychology devoted to the study, assessment, treatment, and prevention of maladaptive behavior. ' - APA

Basolateral Group

'one of the two main groups of nuclei in the amygdala within the brain and the largest portion of the amygdaloid complex. Its nuclei receive neuromodulatory input from various neurotransmitter systems in the basal forebrain and brainstem, are connected particularly with higher order sensory and limbic association areas, and project to the central amygdala. They are implicated in fear conditioning and emotional learning. Also called basolateral complex.' - APA

Borderline Personality Disorder

'in DSM–IV–TR and DSM–5, a personality disorder characterized by a long-standing pattern of instability in mood, interpersonal relationships, and self-image that is severe enough to cause extreme distress or interfere with social and occupational functioning. Among the manifestations of this disorder are (a) self-damaging behavior (e.g., gambling, overeating, substance use); (b) intense but unstable relationships; (c) uncontrollable temper outbursts; (d) uncertainty about self-image, gender, goals, and loyalties; (e) shifting moods; (f) self-defeating behavior, such as fights, suicidal gestures, or self-mutilation; and (g) chronic feelings of emptiness and boredom.' - APA


'the science that deals with the biological basis of behavior, thoughts, and emotions and the reciprocal relations between biological and psychological processes. It also addresses topics such as behavior-changing brain lesions, chemical responses in the brain, and brain-related genetics. It includes such fields as behavioral neuroscience, clinical neuroscience, cognitive neuroscience, behavioral endocrinology, and psychoneuroimmunology. Also called biological psychology; physiological psychology; psychobiology.' - APA

Biopolar Neuron

'a neuron with only two extensions—an axon and a dendrite—that run from opposite sides of the cell body. Cells of this type are found primarily in the retina and also elsewhere in the nervous system. Also called bipolar cell.' - APA

Behavior Therapy

'a form of psychotherapy that applies the principles of learning, operant conditioning, and classical conditioning to eliminate symptoms and modify ineffective or maladaptive patterns of behavior. The focus of this therapy is upon the behavior itself and the contingencies and environmental factors that reinforce it, rather than exploration of the underlying psychological causes of the behavior. A wide variety of techniques are used in behavior therapy, such as behavior rehearsal, biofeedback, modeling, and systematic desensitization. Also called behavioral psychotherapy; conditioning therapy.' - APA

Broca's Area

'a region of the posterior portion of the inferior frontal convolution of a cerebral hemisphere that is associated with the production of speech. It is located on the left hemisphere of right-handed and of most left-handed individuals. [discovered in the 1860s and studied and researched by Paul Broca]' - APA

Basal Ganglia

'a group of nuclei (neuron cell bodies) deep within the cerebral hemispheres of the brain that includes the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus. The putamen and globus pallidus are together known as the lenticular (or lentiform) nucleus, the lenticular nucleus and caudate nucleus are together known as the corpus striatum, and the caudate nucleus and putamen are together called the striatum. The basal ganglia are involved in the generation of goal-directed voluntary movement. Also called basal nuclei.' - APA

Bipolar Disorder

'any of a group of mood disorders in which symptoms of mania and depression alternate. In DSM–IV–TR and DSM–5, the group includes primarily the following subtypes: bipolar I disorder, in which the individual fluctuates between episodes of mania or hypomania and major depressive episodes or experiences a mix of these: bipolar II disorder, in which the individual fluctuates between major depressive and hypomanic episodes; and cyclothymic disorder. The former official name for bipolar disorders, manic-depressive illness, is still in frequent use.' - APA

Cognitive Psychology

'the branch of psychology that explores the operation of mental processes related to perceiving, attending, thinking, language, and memory, mainly through inferences from behavior. The cognitive approach, which developed in the 1940s and 1950s, diverged sharply from contemporary behaviorism in (a) emphasizing unseen knowledge processes instead of directly observable behaviors and (b) arguing that the relationship between stimulus and response was complex and mediated rather than simple and direct. Its concentration on the higher mental processes also contrasted with the focus on instincts and other unconscious forces typical of psychoanalysis. More recently, cognitive psychology has been influenced by approaches to information processing and information theory developed in computer science and artificial intelligence. See also cognitive science.' - APA

Counseling Psychology

'the branch of psychology that specializes in facilitating personal and interpersonal functioning across the lifespan. Counseling psychology focuses on emotional, social, vocational, educational, health-related, developmental, and organizational concerns—such as improving well-being, alleviating distress and maladjustment, and resolving crises—and addresses issues from individual, family, group, systems, and organizational perspectives. The counseling psychologist has received professional education and training in one or more counseling areas, such as educational, vocational, employee, aging, personal, marriage, or rehabilitation counseling. In contrast to a clinical psychologist (see clinical psychology), who usually emphasizes origins of maladaptations, a counseling psychologist emphasizes adaptation, adjustment, and more efficient use of the individual’s available resources.' - APA

Couples Therapy

'therapy in which both partners in a committed relationship are treated at the same time by the same therapist or therapists. Couples therapy is concerned with problems within and between the individuals that affect the relationship. For example, one partner may have undiagnosed depression that is affecting the relationship, or both partners may have trouble communicating effectively with one another. Individual sessions may be provided separately to each partner, particularly at the beginning of therapy; most of the course of therapy, however, is provided to both partners together. Couples therapy for married couples is known as marital therapy.' - APA

Cerebrospinal Fluid (CSF)

'the fluid within the central canal of the spinal cord, the four ventricles of the brain, and the subarachnoid space of the brain. It serves as a watery cushion to protect vital tissues of the central nervous system from damage by shock pressure, and it mediates between blood vessels and brain tissue in exchange of materials, including nutrients.' -APA

Cell Body

'the part of a neuron (nerve cell) that contains the nucleus and most organelles. Also called perikaryon; soma.' - APA

Cerebral Hemisphere

'either half (left or right) of the cerebrum. The hemispheres are separated by a deep longitudinal fissure, but they are connected by commissural, projection, and association fibers so that each side of the brain normally is linked to functions of tissues on either side of the body. See also hemispheric lateralization.' - APA

Clinical Psychology

'the branch of psychology that specializes in the research, assessment, diagnosis, evaluation, prevention, and treatment of emotional and behavioral disorders. Clinical psychologists are doctorate-level professionals who have received training in research methods and techniques for the diagnosis and treatment of various psychological disorders. They work primarily in health and mental health clinics, in research, in academic settings, or in group and independent practices. They also serve as consultants to other professionals in the medical, legal, social-work, and community-relations fields. Clinical psychologists comprise approximately one third of the psychologists working in the United States and are governed by the code of practice of the American Psychological Association and by state licensing requirements.' - APA


'the largest part of the brain, forming most of the forebrain and lying in front of and above the cerebellum. It consists of two cerebral hemispheres bridged by the corpus callosum. Each hemisphere is divided into four main lobes: the frontal lobe, occipital lobe, parietal lobe, and temporal lobe. The outer layer of the cerebrum—the cerebral cortex—is intricately folded and composed of gray matter. Also called telencephalon. [Latin, literally: “brain”]' - APA

Cognitive Therapy (CT)

'a form of psychotherapy based on the concept that emotional and behavioral problems in an individual are, at least in part, the result of maladaptive or faulty ways of thinking and distorted attitudes toward oneself and others. The objective of the therapy is to identify these faulty cognitions and replace them with more adaptive ones, a process known as cognitive restructuring. The therapist takes the role of an active guide who attempts to make the client aware of these distorted thinking patterns and who helps the client correct and revise his or her perceptions and attitudes by citing evidence to the contrary or by eliciting it from the client. See also cognitive behavior therapy. Also called Beck therapy. [developed by Aaron T. Beck]' - APA

Central Canal

'the channel in the center of the spinal cord, which contains cerebrospinal fluid.' - APA

Central Nervous System (CNS)

'the entire complex of neurons, axons, and supporting tissue that constitute the brain and spinal cord. The CNS is primarily involved in mental activities and in coordinating and integrating incoming sensory messages and outgoing motor messages. Compare peripheral nervous system.' - APA


(pl. Cerebella)

'a portion of the hindbrain dorsal to the rest of the brainstem, to which it is connected by the cerebellar peduncles. The cerebellum modulates muscular contractions to produce smooth, accurately timed ballistic movements; it helps maintain equilibrium by predicting body positions ahead of actual body movements, and it is required for some kinds of motor conditioning. [Latin, literally: “little brain,” diminutive of cerebrum]' - APA

Cerebral Cortex

'the layer of gray matter that covers the outside of the cerebral hemispheres in the brain and is associated with higher cognitive functions, such as language, learning, perception, and planning. It consists mostly of neocortex, which has six main layers of cells; regions of cerebral cortex that do not have six layers are known as allocortex. Differences in the cytoarchitecture of the layers led to the recognition of distinct areas, called Brodmann’s areas, many of which are known to serve different functions.' - APA

Corticomedial Group

'one of the two main groups of nuclei in the amygdala within the brain. It includes the central nucleus and receives mainly olfactory and pheromonal information; its output, via the stria terminalis, is to the hypothalamus and the basomedial forebrain. See also basolateral group.' - APA

Client-Centered Therapy

'a form of psychotherapy developed by Carl Rogers in the early 1940s. According to Rogers, an orderly process of client self-discovery and actualization occurs in response to the therapist’s consistent empathic understanding of, acceptance of, and respect for the client’s frame. The therapist sets the stage for personality growth by reflecting and clarifying the ideas of the client, who is able to see himself or herself more clearly and come into closer touch with his or her real self. As therapy progresses, the client resolves conflicts, reorganizes values and approaches to life, and learns how to interpret his or her thoughts and feelings, consequently changing behavior that he or she considers problematic. It was originally known as nondirective counseling or nondirective therapy, although this term is now used more broadly to denote any approach to psychotherapy in which the therapist establishes an encouraging atmosphere but avoids giving advice, offering interpretations, or engaging in other actions to actively direct the therapeutic process. Also called client-centered psychotherapy; person-centered therapy; Rogerian therapy.' - APA

Corpus Callosum

'a large tract of nerve fibers running across the longitudinal fissure of the brain and connecting the cerebral hemispheres: It is the principal connection between the two sides of the brain. The largest of the interhemispheric commissures, it is known as the great commissure. ' - APA

Cervical Nerve

'any of the eight spinal nerves in the neck area. Each has a dorsal root that is sensory in function and a ventral root that has motor function.' - APA

Commissural Fiber

'an axon from any of various neurons that connect the same or equivalent structures in the left and right cerebral hemispheres.' - APA

Correctional Psychology

'a branch of forensic psychology concerned with the application of counseling and clinical techniques to criminal and juvenile offenders in penal and correctional facilities (e.g., reformatories, penitentiaries). Correctional psychologists also participate professionally in court activities, probation departments, parole boards, prison administration, supervision of inmate behavior, and programs for the rehabilitation of offenders.' - APA

Conjoint Therapy

'therapy in which the partners in a relationship or members of a family are treated together in joint sessions by one or more therapists, instead of being treated separately. Also called conjoint counseling. ' - APA

Cognitive Behaviour Therapy (CBT)

'a form of psychotherapy that integrates theories of cognition and learning with treatment techniques derived from cognitive therapy and behavior therapy. CBT assumes that cognitive, emotional, and behavioral variables are functionally interrelated. Treatment is aimed at identifying and modifying the client’s maladaptive thought processes and problematic behaviors through cognitive restructuring and behavioral techniques to achieve change. Also called cognitive behavior modification; cognitive behavioral therapy' - APA

Cognitive Analytic Therapy

'a time-limited, collaborative psychotherapy that emphasizes schemas and integrates principles and techniques from psychodynamic psychotherapy and cognitive behavior therapy. [developed in the 1980s by British psychiatrist Anthony Ryle (1927–  )]' - APA