Magnetic Resonance Imaging and Time of the Day

Paper Summary:

In this article, the writer maintains that developers of research designs need to take all relevant processes into account if their results are to have validity. The writer notes that many researchers conducting functional magnetic resonance imaging (MRI) tests fail to take the time of day into consideration. The writer points out that this can lead to error given that cortisol levels are different throughout the course of a day. This is important because cortisol can cross the blood-brain barrier and bind to receptors in the hippocampus and frontal lobe. The writer explains that this can then have an impact on the neural activation/deactivation process, meaning the BOLD (blood oxygen level dependent) in the MRI study and produce results that will not be properly interpreted unless the time of day is included as a variable.

From the Paper:

"Higher levels of cortisol are associated with stress, and cortisol levels vary throughout the day just as levels of stress will vary throughout the day. Because cortisol can cross the blood-brfain barrier and bind to the hippocampus, levles of cortisol can have an effect on the neural activation and deactivation of the BOLD levels and so alter the results of the MRI. Time of day thus becomes an element in the process so that the clinician knows what time of day the examination was made and how high the levels of cortisol might be at different tiemns of the day."

Sample of Sources Used:

• "Blood Pressure Levels Influenced by Time of Day and Year." Medical News Today (16 May 2005). January 29, 2007. http://www.medicalnewstoday.com/medicalnews.php?newsid=24429.
• Shaw, Phyllis. "Gadolinium: Highlighting MRI: Key to Revelation?" Inside MS (Summer, 1990). January 29, 2007. http://findarticles.com/p/articles/mi_m0850/is_n3_v8/ai_9369099.
• Silcox, D.H., W.C. Horton, and A.M. Silverstein. "MRI of lumbar intervertebral discs." Spine (1 April 1995), 807-811. January 29, 2007. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=7701395&dopt=Abstract.
• Stonestreet, Barbara S. Grazyna B. Sadowska, Amanda J. McKnight, Clifford Patlak, and Katherine H. Petersson. "Exogenous and Endogenous Corticosteroids Modulate Blood-brain Barrier Development in the Ovine Fetus. American Journal of Physiology 279. January 29, 2007. http://ajpregu.physiology.org/cgi/content/full/279/2/R468.
• Tessner, K.D., Elaine F. Walker, Karen Hochman, and Stephan Hamann. "Cortisol Responses of Healthy

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