Psychophysiology is the branch of psychology that studies the relationship between the physiological processes and behavior. It seeks to understand how biological processes and behavior are connected, and how they interact with each other. In particular, psychophysiology examines the relationship between the nervous system, the endocrine system, and behavior.

Examples of research in psychophysiology include studies on the brain waves that occur during different states of consciousness, such as sleep or meditation. Psychophysiology also investigates the relationship between physiological changes and emotions, such as the physiological changes that occur during anxiety or stress. Other areas of research in psychophysiology include the study of the autonomic nervous system, which controls many involuntary bodily functions, such as heart rate, blood pressure, and digestion.

One of the most widely used techniques in psychophysiology is electroencephalography (EEG), which records the electrical activity of the brain. EEG is used to study the brain waves that occur during different states of consciousness, such as sleep or meditation, and can be used to diagnose various neurological conditions.

Another commonly used technique in psychophysiology is electromyography (EMG), which records the electrical activity of muscles. EMG is used to study muscle tension and relaxation, and can be used to diagnose neuromuscular disorders.

Other techniques used in psychophysiology include electrocardiography (ECG), which records the electrical activity of the heart, and electrodermal activity (EDA), which measures changes in skin conductance in response to emotional or psychological stimuli.

Similar to psychophysiology, cognitive neuroscience is a branch of psychology that studies the relationship between the brain and behavior. However, while psychophysiology focuses on the relationship between the physiological processes and behavior, cognitive neuroscience focuses on the relationship between the brain and cognitive processes such as attention, memory, and language.

Another related field is psychoneuroimmunology, which studies the relationship between the nervous system, the immune system, and behavior. Psychoneuroimmunology examines how psychological and social factors can affect the immune system and influence the onset and progression of diseases.

In summary, psychophysiology is a field of psychology that examines the relationship between physiological processes and behavior. It uses a range of techniques to study the relationship between the nervous system, the endocrine system, and behavior, and has important applications in fields such as clinical psychology and neuroscience.