Ninth Edition CoverGraziano & Raulin
Research Methods (9th edition)

The Impact of Other Disciplines

Developments in related disciplines can have a significant positive impact on the discipline of psychology. One of the best examples is the study of neurological influences on human behavior.

Developments in the field of biochemistry, which permitted much finer analyses of organic chemicals, made possible the discovery that there are many more neurotransmitters involved in the functioning of the central nervous system than previously believed. This explosion in the number of known chemical transmission agents required scientists to rethink the role of neurotransmitters. The concept of specific transmitter influences in precise locations within the brain and other parts of the central nervous system became a much more intellectually appealing theory. But how do we study specific influences of specific neurotransmitters in specific locations in the brain? Much of the previous research on neurotransmitters operated under the assumption that there are general levels of the chemicals in the system, and the procedures used for measuring the chemicals were usually nonspecific with respect to the location of the action of each transmitter. There was a need to develop techniques to sample from specific locations within the brain. Because brain-functioning processes are part of the living organism and not only a matter of the organism’s structure, it was necessary to accomplish the sampling without damaging the organism. A sampling of brain tissue at autopsy would provide little useful information. It would also be enormously helpful to be able to experimentally manipulate specific neurotransmitters at specific locations. A procedure known as micro-iontophoresis (Curtis & Crawford, 1969) was developed, which allowed the researcher to inject specific amounts of certain substances into the synapses of neurons while the animal was awake and functioning. For the first time, this new technology offered the possibility of using experimental methods to investigate the relationship between neurotransmitters functioning at specific locations of the brain and their effect on the behavior of living organisms.

The research of Elaine Hull and her students illustrates some of these techniques as well as even newer technologies. Dr. Hull has been studying the neuromechanisms controlling the sexual behavior of rats. Presumably similar mechanisms control the sexual behavior of humans. She and her students have refined techniques to implant surgically microcannulae (tiny tubes) into specific locations of a rat’s brain. With such an implant the animal is able to function normally without discomfort, but the researcher is able to influence the functioning of specific regions of the brain by injecting substances through the cannula. It is important to note that the techniques must not cause pain to the animal, because even a rat is less likely to engage in sex if it has a headache. Her research (e.g., Hull et al., 1991; Warner et al., 1991) systematically identified the brain mechanisms that control sexual motivation, motor behavior related to sexual activity, and sexual reflexes. Her work is now incorporating a new, even more amazing technique. Being able to inject specific neurotransmitter agonists (substances that enhance the action of specific neurotransmitters) or antagonists (substances that block the action of specific neurotransmitters) gives considerable information about the functional mechanisms of a system. However, it is useful to observe the normal functioning of a system. Crude methods sampled specific locations of a rat’s brain at key points in sexual behavior, but the techniques involved immediate removal of the section of the brain and a chemical fixing of that section for analysis. An alternative is to sample the chemical composition in an alert and active animal using a technique called microdialysis. This technique implants a cannula in a specific location; but the cannula has a tube within a tube, with the outer tube having a chemically porous tip. Neurotransmitters diffuse across this tip into the fluid that is pumped slowly through the cannula. The levels of neurotransmitters in the fluid can then be measured. Also, drugs can be added to the fluid and diffused into the brain. This technique will not only verify earlier findings, but can also give clues about the temporal sequence of brain actions involved in sexual activity. As is always the case in science, these new techniques are providing the answers to some important questions, and in the process are raising yet more questions that demand still newer techniques. Using these and other techniques, Hull and her colleagues have confirmed through a series of studies (Hull et al., 1995, 1999) an earlier theory that a specific brain region (the medial preoptic area) seems to control sexual motivation. Here the developments in other scientific disciplines—biochemistry and neuroscience—have affected research in another science, psychology.


Curtis, D. R., & Crawford, J. M. (1969). Central synaptic transmission--microelectrophoretic studies. Annual Review of Pharmacology, 9, 209-240.

Hull, E. M., Du, J., Lorrain, D. S., & Matuszewich, L. (1995). Extracellular dopamine in the medial preoptic area: Implications for sexual motivation and hormonal control of copulation. Journal of Neuroscience, 15, 7465-7471.

Hull, E. M., Lorrain, D. S., Du. J., Matuszewich, L., Lumley, L. A., Putnam, S. K., & Moses, J. (1999). Hormone-neurotransmitter interactions in the control of sexual behavior. Behavioural Brain Research, 105, 105-116.

Hull, E. M., Weber, M. S., Eaton, R. C., Dua, R., Markowski, V. P., Lumley, L., & Moses, J. (1991). Dopamine receptors in the ventral tegmental area affect motor, but not motivational or reflexive, components of copulation in male rats. Brain Research, 554, 72–76.

Warner, R. K., Thompson, J. T., Markowski, V. P., Loucks, J. A., Bazzett, T. J., Eaton, R. C., & Hull, E. M. (1991). Microinjection of the dopamine antagonist cis-flupenthixol into the MPOA impairs copulation, penile reflexes and sexual motivation in male rats. Brain Research, 540, 177–182.