Friday, 6 January 2012
fMRI relies on oxygenated changes in the blood which are a result of blood flow and/or blood volume in the body and brain. Caffeine apparently acts as a cerebral vasoconstrictor and has positive effects on the quality of data gained from fMRI studies. This is accomplished by decreasing the baseline BOLD signal (blood oxygen level dependent) which then creates a greater percent change when a task is completed.
This plus side of this interesting find is that it will increase the detection of activation in the brain whilst investigating models or paradigms.
The figure above shows fMRI data from a participant who performed a task before having caffeine exposure and then again after. The top row of data is prior and the bottom is post. As you can see, due to the lower baseline, there was a greater percent change in the participant post caffeine which shows us greater activation.It is important to note here that the same statistical model and analysis was used for both.
This method is great but probably only if it is done along side non-caffeinated imaging studies. This would be because doing it on it's own runs the risk of showing us activated areas which are irrelevant.
However it does have the possibility to increase the sensitivity of our imaging studies without the need for expensive machinery or complex statistical models.
This then poses a more interesting question of; Are any fMRI studies investigating caffeine accurate?
If caffeine lowers the baseline BOLD signal and thus increases the percent change of blood flow when neural activation is observed - are any results accurate?
I suppose this poses a rather phenomenological question of what is really being observed - since the signal change is the natural effect caffeine has on the human brain then you could argue that yes it is. On the other hand you could see that the results of any caffeine fMRI study to be "extreme" as a result of the signal change and should be analysed with care. The obvious way around this is to give participants caffeine supplements after testing the baseline after all, the baseline should be as neutral as possible.
But then again, have you ever tried to have a drink whilst laying down in an fMRI machine? I would imagine it's rather difficult.
Full Text : http://www.radiology.northwestern.edu/research/brain/neuroimaging/using-caffeine-as-a-contrast-booster-in-fmri
This then lead me to think about the effects of caffeine on other forms of imaging tools - with a focus on EEG. Since EEG relies on the neural activation of observed regions of the outer cortex it could also be affected by caffeine.