Physiological and Comparative Psychology share a great deal in common. As such, it is offered as a field of specialization in many educational institutions. Experiments conducted in physiology influenced the development of scientific psychology.

Mental activities are influenced by physiological structures and functions. Physiological psychology primarily emphasizes the study of biological structures and functions, and their role in shaping behaviors. The physiological psychologists study how the brain, the nervous system, the glands, and the sense organs influence mental activities.

The comparative psychology deals with the similarities and differences in the behaviors of animals belonging to different species. The major issues in these two areas include neural basis of behavior, heredity and instincts, behavior genetics, evolution of behavior, sleeping, eating, and drinking behaviors, states of consciousness, the functions of nervous and glandular systems, neuropsychology, and the effects of drugs. Experimental and observational methods are used to gain knowledge about different physiological subsystems and the behaviors of different species.