All behaviour is heritable to some degree, but genes do not operate in isolation from the environment. The environment shapes how our genes are expressed and our genes shape the environment. Genes are the carriers of genetic information. Gene expression is the expression of a gene to produce a protein. Psychopathology is polygenic, there is not a single gene that causes a disorder. Heritability refers to the extent to which variability in a particular behaviour in a population can be accounted for by genetic factors. Shared environment factors are factors that members of a family have in common. Nonshared environment factors are factors that are distinct among members of a family.

Behaviour genetics is the study of the degree to which genes and environmental factors influence behaviour. Molecular genetics seeks to identify particular genes and their functions. A genetic polymorphism refers to a difference in the DNA sequence on a gene that has occurred in a population. Single nucleotide polymorphisms refer to differences between people in a single nucleotide.  A gene-environment interaction means that a given person’s sensitivity to an environmental event is influenced by genes. Epigenetics is the study of how the environment can alter gene expression.

The neuroscience paradigm holds that psychological disorders are linked to aberrant processes in the brain. Norepinephrine is a neurotransmitter that communicates with the sympathetic nervous system. It is involved in producing high states of arousal. An agonist is a drug that stimulates a particular neurotransmitter’s receptor. An antagonist is a drug that works on a neurotransmitter’s receptor to dampen the activity of that neurotransmitter.

Nerves converge and messages are integrated from different centres in nuclei. Pruning is the elimination of a number of synaptic connections. The hypothalamic-pituitary-adrenal (HPA) axis is central to the body’s response to stress. Psychoneuroimmunology studies how psychological factors influence the immune system. Natural immunity is the body’s first line of defence. It consists of cells attacking the invaders. Specific immunity involves cells that respond more slowly to infection. Cytokines are activated by the immune system during infection and help initiate bodily responses to infection such as fever.

The cognitive behavioural paradigm makes use of learning principles and cognitive science. Problem behaviour is reinforced by getting attention (1), escaping from tasks (2), generating sensory feedback (3) and gaining access to desirable things or situations (4). Maintaining the effect of treatment is difficult.

Behavioural activation (BA) therapy involves helping a person engage in tasks that provide an opportunity for positive reinforcement. Behaviour therapy minimizes the importance of thinking and feeling. Cognition is a term that groups together the mental processes of perceiving, recognizing, conceiving, judging and reasoning. Implicit memory refers to the idea that a person can, without being aware of it, be influenced by prior learning.

Cognitive behaviour therapy (CBT) incorporates theory and research on cognitive processes. Cognitive restructuring refers to changing a pattern of thought.

Emotions influence how we respond to problems and challenges in our environment. They help us organize our thoughts and actions. They guide our behaviour. Emotions are short-lived states, feelings. Moods are emotional experiences that endure for a longer period. Emotions include expressive (behavioural), experiential (subjective experience) and physiological (changes in body) components. Ideal affect refers to the emotional state an individual wants to experience.

There are cultural influences on the symptoms expressed in different disorders, the availability of treatment and the willingness to seek treatment. The quality of relationships influences different disorders. Stress and major life events also influence different disorders. Interpersonal factors are important in different disorders.

Psychoeducation focuses on improving understanding of the disorder, reducing expressed family criticism and hostility and helping families learn skills for managing symptoms. Transference refers to a person’s responses to the analyst that seem to reflect attitudes and ways of behaving toward important people in the patient’s past. The object relations theory stresses the importance of long-standing patterns in close relationships.

Interpersonal therapy emphasizes the importance of current relationships in a person’s life and how problems in these relationships can contribute to psychological symptoms. The therapist encourages the patient to identify feelings about his or her relationships and to express these feelings. In IPT, four interpersonal issues are assessed: unresolved grief (1), role transitions (2), role disputes (3) and interpersonal or social deficits (4).

The diathesis-stress paradigm links genetic, neurobiological, psychological and environmental factors. It focuses on a predisposition for a disorder (diathesis) and environmental factors (stress). Diathesis refers to a constitutional predisposition toward illness. Both diathesis and stress are necessary for the development of disorders.