The researchers in the current study designed a test called the Montreal Imaging Stress Tast (MIST). They wanted to be able to directly measure stress by "inducing and measuring in functional imaging environments." PET and fMRI are utilized in 3 independent studies. For the first study, ten healthy people were tracked for dopamine release, which is indicated by the ventral striatum, by a PET scan. In the second study, ten males were investigated under PET on the "effects of acute stress perception in the human brain on cerebral blood flow." Finally, the third study investigated 22 males on "the effects of acute stress perception" using the fMRI. In each study, there were 3 conditions: rest, control, and experimental. The MIST is a computer program that evaluates a mental math task based on time it took to answer the question, whether it was right or wrong, and it also indicates how the subject is doing compared to the overall average score of all subjects participating in the study. At first, participants are given a five minute run testing session, which provides an average baseline of how long it takes for them to do a mental math task in general. After that, the participant undergoes the experimental condition, where a time limit is set at 10 percent lower than their baseline, to induce stress. Also, the researcher tells the subject they are required to get a certain percentage of problems correct for them to be included in the study. Futhermore, the researcher tells them their performance is being watched by other researchers. This is the experimental stress condtion. The control group is required to do the same thing, only there are not stressors, such as time limit, evaluated performance, and the requirment of a certain percentage being correct. This group was matched with the experimental group in cerebral activation. The rest condition provided a cerebral activation baseline and the subjects were asked to sit still and look at an empty screen or close their eyes, depending on which study was being performed. This rest lasted approximately one to three minutes. Throughout the recordings of fMRI and PET scans, the subject was asked to saturate a salivette for two minutes in order to check for cortisol levels.
Study 1: They used a PET scan to track "dopamine release from the basal ganglia." They performed the 5 minute testing session, repeated the MIST five times for six minutes, and then was scanned for dopamine release. Saliva samples were taken every twelve minutes throughout the experiment. During the rest condition, they were asked to keep their eyes closed. In order for cortisol levels to be similar each day, the subjects were tested at the same time each day.
Study 2: They used a PET scan to investigate the "cerebral blood flow tracer, OH2O." They repeated each condtion three times in a row. The rest condition required subjects to lie still and look at the blank screen. The tracer was injected every ten minutes and saliva samples were obtained before and after the rest, the control, and the experimental condtions.
Study 3: They used fMRI for each of the three conditions. The investigator would give the subject negative feedback about their performance on the MIST. Saliva samples were taken before the fMRI runs.
To analyze the data in both PET and fMRI studies, the researchers made three comparisons between the experimental and control, experimental and rest, and control and rest to "determine task-specific changes in regional cerebral blood flow." They utilized mixed design ANOVA to test for studies one and two, but used a repeated measure ANOVA for study three.
In conclusion, the researchers reported their MIST test raised cortisol levels, which determined the task was indeed stressful. They also concluded that their test was "consistent with previous studies involving mental arithmentic, including activation of the visual association cortex for the processing of visual stimuli, activation of the motor cortex....activation of the angular cortex as a result of mental arithmetic and activation of the cerebellum."
I found this study interesting because it helped me alot when designing our stress lab. I believe our conditions will be somewhat similar, though not exact, and we will also be measuring cortisol levels.
Dedovic, K., Renwick, R., Mahani, N.K., Engert, V., Lupien, S.J., & Pruessner, J.C. (2005).
The Montreal Imaging Stress Task: using functional imaging to investigate the effects of perceiving and
processing psychosocial stress in the human brain. Journal of Psychiatry & Neuroscience, 30(5), 319-325. Retrieved from EbscoHost. doi: not found.http://ezproxy.utm.edu/login?url=http://search.ebscohost.com/login.aspx?direct=true&db=aph&AN=17998027&site=ehost-live
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