Biochemistry is the chemistry of life. Biochemists study the molecules and chemical reactions catalyzed by enzymes that take place in all living organisms. See the article on molecular biology for a diagram and description of the interrelationship between biochemistry, molecular biology, and genetics.

Cognitive psychology
The psychological science which studies cognition, the mental processes that are hypothesised to underlie behavior. This covers a broad range of research domains, examining questions about the workings of memory, attention, perception, knowledge representation, reasoning, creativity and problem solving.

Ethology is the scientific study of animal behaviour (particularly of social animals such as primates and canids.), and is a branch of zoology. A scientist who practises ethology is called an ethologist.

A field of study which deals with the structure, development, function, chemistry, pharmacology and pathology of the central or peripheral nervous system. The biological study of the brain is an interdisciplinary field, which involves many levels of study, from the molecular level through the cellular level (individual neurons), the level of relatively small assemblies of neurons like cortical columns, that of larger subystems like that which subserves visual perception, up to large systems like the cerebral cortex or the cerebellum, and at the highest level the nervous system as a whole. At this highest level the field largely merges with cognitive neuroscience, a discipline first populated mostly by cognitive psychologists, currently becoming a dynamic specialty of its own. Thus, the concern of neuroscience includes such diverse topics as the operation of neurotransmitters, how genes contribute to the embryonic development of the nervous system and to learning, the operation of relatively simpler neural structures of other organisms like marine snails, and the structure and functioning of complex neural circuits in perceiving, remembering, and speaking. Closely related and overlapping fields, besides cognitive neuroscience, include neurology, psychopharmacology, aphasiology, neurolinguistics, and several others.

Neurotransmitters are chemicals that are used to relay, amplify and modulate electrical signals between two neurons: the presynaptic neuron and the postsynaptic neuron.

Philosophy of mind
Philosophy of mind is the philosophical study of the nature of the mind, mental events, mental functions, and consciousness.

Psychiatry is a branch of medicine that studies and treats mental and emotional disorders, some of which are listed on the mental illness page. The term alienist is an old term for a psychiatrist.

Psychological testing
Psychological testing is a field characterized by the use of small samples of behavior in order to infer larger generalizations about a given individual. The technical term for psychological testing is psychometrics. By samples of behavior, we mean observations of the individual over a limited amount of time performing tasks which have usually been prescribed beforehand, often with a great deal of research into the responses of members of a norm group. These responses are often compiled into statistical tables that allow the evaluator to compare the behavior of the individual being tested to the responses of the range of responses given by people in the norm group. When multiple tests are administered, the procedure is referred to as full battery assessment.

Psychology is an applied discipline and applied profession concerned with the study of and intervention in mental states, processes, and behavioral patterns of humans and, to an extent, of animals (though the study of animal behavior, ethology, is more often regarded a branch of biology than of psychology). Psychologists also study interactions between individuals and groups of individuals, and between individuals, groups and their environment. Disciplines that are traditionally considered to intersect with psychology are sociology, anthropology, biology, and philosophy, but more recently fields such as neuroscience, political science, media studies and gender studies have also come to be seen as closely related to psychology.

Psychometrics is the field of study (connected to psychology and statistics) concerned with the measurement of "psychological" aspects of a person such as knowledge, skills, abilities, or personality. The field of Psychometrics is primarily concerned with differences between individuals and employs statistical tools such as normal distribution and factor analysis. Measurement of these unobservable phenomena is difficult and much of the research and accumulated art of this discipline is designed to reliably define and then quantify. Critics, including "hard science" practitioners and social activists, have argued that such definition and quantification is impossibly difficult and that such measurements are very often misused (although users of psychometric techniques can reply that their critics often misuse data by not assessing them with psychometric criteria). Figures who made significant contributions to psychometrics include Karl Pearson, L. L. Thurstone, Georg Rasch and Arthur Jensen. Significant critics include the late Stephen Jay Gould.

Sociology is the study of the social lives of humans, groups, and societies, sometimes defined as the study of social interactions. It is a relatively new academic discipline that evolved in the early 19th century.