For example, psychologists are interested in why we may fear spiders and physiologists may be interested in the input/output system of the amygdala. A psychophysiologist will attempt to link the two. He might, for example, try to explain arachnophobia in terms of impulses coming in and out of the amygdala. However, psychophysiologists almost always study the psychological/physiological link in intact human subjects. While early psychophysiologists almost always examined the impact of psychological states on physiological system responses, since the 1970s, psychophysiologists also study the impact of physiological states and systems on psychological states. It is this perspective of studying the interface of mind and body that makes psychophysiologists most distinct.
Psychophysiology is different from physiological psychology in that psychophysiology looks at the way psychological activities produce physiological responses, while physiological psychology looks at the physiological mechanisms which lead to psychological activity. Historically, most psychophysiologists tended to examine the physiological responses and organ systems innervated by the autonomic nervous system. More recently, psychophysiologists have been equally, or potentially more, interested in the central nervous system, exploring cortical brain potentials such as the many types of event-related potentials (ERPs), brain waves, functional neuroimaging (fMRI), PET, MEG, etc.
A psychophysiologist may look at how exposure to a stressful situation will produce a result in the cardiovascular system such as a change in heart rate (HR), vasodilation/vasoconstriction, myocardial contractility, or stroke volume. A physiological psychologist may look at how one cardiovascular event may influence another cardiovascular or endocrine event, or how activation of one neural brain structure exerts excitatory activity in another neural structure which then induces an inhibitory effect in some other system. Often, physiological psychologists examine the effects that they study in infrahuman subjects using surgical or invasive techniques and processes.
Psychophysiology is closely related to the field of Neuroscience and Social neuroscience, which primarily concerns itself with relationships between psychological events and brain responses. Psychophysiology is also related to the medical discipline known as psychosomatics.
While psychophysiology was a discipline off the mainstream of psychological and medical science prior to roughly the 1960 and 1970s, more recently, psychophysiology has found itself positioned at the intersection of psychological and medical science, and its popularity and importance have expanded commensurately with the realization of the inter-relatedness of mind and body.