Biological psychology
In psychology, biological psychology, also known as biopsychology and psychobiology, is the application of the principles of biology to the study of mental processes and behavior.  A psychobiologist, for instance, may compare the imprinting behavior in goslings to the early attachment behavior in human infants and construct theory around these two phenomena.  Biological psychologists may often be interested in measuring some biological variable, e.g. an anatomical, physiological, or genetic variable, in an attempt to relate it quantitatively or qualitatively to a psychological or behavioral variable, and thus contribute to evidence based practice.

# History
The study of biological psychology dates back to Avicenna (980-1037), a Persian psychologist and physician who in The Canon of Medicine, recognized physiological psychology in the treatment of illnesses involving emotions, and developed a system for associating changes in the pulse rate with inner feelings, which is seen as an anticipation of the word association test. Avicenna also gave psychological explanations for certain somatic illnesses, and he always linked the physical and psychological illnesses together. He explained that humidity inside the head can contribute to mood disorders, and he recognized that this occurs when the amount of breath changes: happiness increases the breath, which leads to increased moisture inside the brain, but if this moisture goes beyond its limits, the brain would lose control over its rationality and lead to mental disorders.
Biological psychology as a scientific discipline later emerged from a variety of scientific and philosophical traditions in the 18th and 19th centuries.  In philosophy, men like Rene Descartes proposed physical models to explain animal and human behavior. Descartes, for example, suggested that the pineal gland, a midline unpaired structure in the brain of many organisms, was the point of contact between mind and body.  Descartes also elaborated on a theory in which the pneumatics of bodily fluids could explain reflexes and other motor behavior. This theory was inspired by moving statues in a garden in Paris.
Other philosophers also helped give birth to psychology.  One of the earliest textbooks in the new field, The Principles of Psychology by William James (1890), argues that the scientific study of psychology should be grounded in an understanding of biology:
James, like many early psychologists, had considerable training in physiology.  The emergence of both psychology and biological psychology as legitimate sciences can be traced from the emergence of physiology from anatomy, particularly neuroanatomy.  Physiologists conducted experiments on living organisms, a practice that was distrusted by the dominant anatomists of the 18th and 19th centuries. The influential work of Claude Bernard, Charles Bell, and William Harvey helped to convince the scientific community that reliable data could be obtained from living subjects.
The term "psychobiology" has been used in a variety of contexts, but was likely first used in its modern sense by Knight Dunlap in his book An Outline of Psychobiology (1914).  Dunlap also founded the journal Psychobiology.  In the announcement of that journal, Dunlap writes that the journal will publish research "...bearing on the interconnection of mental and physiological functions", which describes the field of biological psychology even in its modern sense.

# Relationship to other fields of psychology and biology
In many cases, humans may serve as experimental subjects in biological psychology experiments; however, a great deal of the experimental literature in biological psychology comes from the study of non-human species, most frequently rats, mice, and monkeys.  As a result, a critical assumption in biological psychology is that organisms share biological and behavioral similarities, enough to permit extrapolations across species.  This allies biological psychology closely with comparative psychology, evolutionary psychology, and evolutionary  biology.  Biological psychology also has paradigmatic and methodological similarities to neuropsychology, which relies heavily on the study of the behavior of humans with nervous system dysfunction (i.e., a non-experimentally based biological manipulation).
Synonyms for biological psychology include biopsychology, behavioral neuroscience, and psychobiology .  Physiological psychology is another term often used synonymously with biological psychology, though some authors would make physiological psychology a subfield of biological psychology, with an appropriately more narrow definition.

# Research methods
The distinguishing characteristic of a biological psychology experiment is that either the independent variable of the experiment is biological, or some dependent variable is biological.  In other words, the nervous system of the organism under study is permanently or temporarily altered, or some aspect of the nervous system is measured (usually to be related to a behavioral variable).

## Disabling or decreasing neural function
- Lesions - A classic method in which a brain-region of interest is enabled.  Lesions can be placed with relatively high accuracy thanks to a variety of brain 'atlases' which provide a map of brain regions in 3-dimensional stereotactic coordinates.
Electrolytic lesions - Neural tissue is destroyed by the use of electric run through.
Chemical lesions - Neural tissue is destroyed by the infusion of a neurotoxin.
Temporary lesions - Neural tissue is temporarily disabled by cooling or by the use of anesthetics such as tetrodotoxin.
Transcranial magnetic stimulation - A new technique usually used with human subjects in which a magnetic coil applied to the scalp causes unsystematic electrical activity in nearby cortical neurons which can be experimentally analyzed as a functional lesion.
- Electrolytic lesions - Neural tissue is destroyed by the use of electric run through.
- Chemical lesions - Neural tissue is destroyed by the infusion of a neurotoxin.
- Temporary lesions - Neural tissue is temporarily disabled by cooling or by the use of anesthetics such as tetrodotoxin.
- Transcranial magnetic stimulation - A new technique usually used with human subjects in which a magnetic coil applied to the scalp causes unsystematic electrical activity in nearby cortical neurons which can be experimentally analyzed as a functional lesion.
- Psychopharmacological manipulations - A chemical receptor antagonist enduces neural activity by interfering with neurotransmission.  Antagonists can be delivered systemically (such as by intravenous injection) or locally (intracebrally) during a surgical procedure.

## Enhancing neural function
- Electrical Stimulation - A classic method in which neural activity is enhanced by application of a small electrical current (too small to cause significant cell death).
- Psychopharmacological manipulations - A chemical receptor agonist facilitates neural activity by enhancing or replacing endogenous neurotransmitters.  Agonists can be delivered systemically (such as by intravenous injection) or locally (intracebrally) during a surgical procedure.
- Transcranial magnetic stimulation - In some cases (for example, studies of motor cortex), this technique can be analyzed as having a stimulatory effect (rather than as a functional lesion) .

## Measuring neural activity
- Single unit recording - The measurement of the electrical activity of one neuron, often in the context of an ongoing behavioral (psychological) task.
- Multielectrode recording - The use of a bundle of fine electrodes to record the simultaneous activity of up to hundreds of neurons.
- fMRI - Functional magnetic resonance imaging, a technique most frequently applied on human subjects, in which changes in cerebral blood flow can be detected in an MRI apparatus and are taken to indicate relative activity of larger scale brain regions (i.e., on the order of hundreds of thousands of neurons).
- Electroencephalography - Or EEG; and the derivative technique of event-related potentials, in which scalp electrodes monitor the average activity of neurons in the cortex (again, used most frequently with human subjects).
- Functional neuroanatomy - In which the expression of some anatomical marker is taken to reflect neural activity.  For example, the expression of immediate early genes is thought to be caused by vigorous neural activity.  Likewise, the injection of 2-deoxyglucose prior to some behavioral task can be followed by anatomical localization of that chemical; it is taken up by neurons that are electrically active.

## Genetic manipulations
- QTL mapping - The influence of a gene in some behavior can be statistically inferred by studying inbred strains of some species, most commonly mice.  The recent sequencing of the genome of many species, most notably mice, has facilitated this technique.
- Selective breeding - Organisms, often mice, may be bred selectively among inbred strains to create a recombinant congenic strain.  This might be done to isolate an experimentally interesting stretch of DNA derived from one strain on the background genome of another strain to allow stronger inferences about the role of that stretch of DNA.
- Genetic engineering - The genome may also be experimentally-manipulated; for example, knockout mice can be engineered to lack a particular gene, or a gene may be expressed in a strain which does not normally do so (the 'knock in').  Advanced techniques may also permit the expression or suppression of a gene to occur by injection of some regulating chemical.

# Topic areas in biological psychology
In general, biological psychologists study the same issues as academic psychologists, though limited by the need to use nonhuman species.  As a result, the bulk of literature in biological psychology deals with mental processes and behaviors that are shared across mammalian species, such as:
- Sensation and perception
- Motivated behavior (hunger, thirst, sex)
- Control of movement
- Learning and memory
- Sleep and biological rhythms
- Emotion
However, with increasing technical sophistication and with the development of more precise noninvasive methods that can be applied to human subjects, biological psychologists are beginning to contribute to other classical topic areas of psychology, such as:
- Language
- Reasoning and decision making
- Consciousness
Biological psychology has also had a strong history of contributing to the understanding of medical disorders, including those that fall under the purview of clinical psychology and psychopathology (also known as abnormal psychology).  Although animal models for all mental illnesses do not exist, the field has contributed important therapeutic data on a variety of conditions, including:
- Parkinson's Disease, a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills and speech.
- Huntington's Disease, a rare inherited neurological  disorder whose most obvious symptoms are abnormal body movements and a lack of coordination. It also affects a number of mental abilities and some aspects of personality.
- Alzheimer's Disease, a neurodegenerative disease that, in its most common form, is found in people over the age of 65 and is characterized by progressive cognitive deterioration, together with declining activities of daily living and by neuropsychiatric symptoms or behavioral changes.
- Clinical depression, a common psychiatric disorder, characterized by a persistent lowering of mood, loss of interest in usual activities and diminished ability to experience pleasure.
- Schizophrenia, a psychiatric diagnosis that describes a mental illness characterized by impairments in the perception or expression of reality, most commonly manifesting as auditory hallucinations, paranoid or bizarre delusions or disorganized speech and thinking in the context of significant social or occupational dysfunction.
- Autism, a brain development disorder that impairs social interaction and communication, and causes restricted and repetitive behavior, all starting before a child is three years old.
- Anxiety, a physiological state characterized by cognitive, somatic, emotional, and behavioral components. These components combine to create the feelings that are typically recognized as fear, apprehension, or worry.
- Drug abuse, including alcoholism

# Nobel Laureates
The following Nobel Prize winners could reasonably be considered biological psychologists.  (This list omits winners who were almost exclusively neuroanatomists or neurophysiologists; i.e., those that did not measure behavioral or psychological variables.)
- Charles Sherrington (1932)
- Edgar Adrian (1932)
- Walter Hess (1949)
- Egas Moniz (1949)
- Georg von Bekesy (1961)
- George Wald (1967)
- Ragnar Granit (1967)
- Konrad Lorenz (1973)
- Niko Tinbergen (1973)
- Karl von Frisch (1973)
- Roger W. Sperry (1981)
- David H. Hubel (1981)
- Torsten N. Wiesel (1981)
- Eric R. Kandel (2000)
- Arvid Carlsson (2000)
- Richard Axel (2004)
- Linda B. Buck (2004)