Greetings everyone,

First, I am not a native English speaker, so apologize my strange expressions sometimes.

I have a question dealing with fMRI. I thought about it and I wanted to ask some people familiar with this topic:

There are excitatory as well as inhibitory neurons in the cortex and their activity comes along with increased metabolsim, which you can see at the fMRI.
So what now if there is a task at which neurons are rendered to inhibit otheres, they would be active now and need more oxygen while the activity of the others goes down and they need then less oxygen. So if these neurons are spatial segregated, can you see the inhibtion at all?
( I am not talking about this “little inhibiton� which always takes place in the cortex, Mexican-Hat curve in the Cortical Columns etc.) Because, at all the fMRI-pics I have never seen an area with decreased activity or heard about it. Is it common that other areas lower their activity in order to make the computation in other ones more effective?
Or lets assume the case that a person has a little neuronal degenerative disease in a small area, which could not be detected via fMRI, so that neurons in this area are always relative inactive and blood flow in this area is always low. Would you see anything uncommon on the fMRI pic? Because you measure only the change in blood flow and not the absolute neuronal activity.

I hope you got my point and can answer my questions. Thanks so far.

PS: Do you know some links or a website with some more fMRI pics, I mean pictures where you can see a persons scan while the person is executing differnet tasks, for example reading or observing a film or doing higher cognitive functions? So I could get a better feeling for the differenmt brain areas.

I'm not too familiar with MRI, but I think that it could be possible to see one area decrease in activity in response to another area's increase. This would be correlatory evidence if you could see it. I don't know if MRI would have the temporal precision necessary and great care would be needed in devising suitable tasks to detect this. There would most likely be too many confounds.
Like allocating attentional resources?

Live MRI's? I'm not sure. Maybe try finding papers on what you're interested in and see if the authors have a website where they might put up small movies of their scans. I don't know if they would, but it would be worth a try.

task-related decreases in BOLD signal have only recently come into vogue, and seem to be related to a "default-mode" or "resting state" network involving posterior cingulate cortex (precuneus), anterior cingulate, and dorsolateral prefrontal cortex. Try Pubmed'ing for "resting state and mri", or try looking up Marcus Raichle's work, to find additional info.

Thanks for the answers so far.



Maybe that, I had no special idea, but it sounds reasonable that the brain allocates the limited resources and turns down the "background" activity in order to accomplish the current task in a fast way, in fast past this task was maybe crucial for survival, so it had obtained priority.
But my question was just if this phenomenon has been observed yet.

usually interneurons are interspersed among pyramidals, so it's quite impossible to segregate inhibitory from excitatory neurons with fmri. Also, keep in mind that fmri is strongly correlated with the input to an area rather than the output electrical activity, so it's possible that the results of such segregation would be misleading.

Usually, fmri images are obtained by subtracting the control from the executing task, so I assume that most people disregard the negative activation values as noise. I guess that's the reason you don't see de-activation results in fmri studies.

but some people have looked at task-induced deactivations in fMRI studies. For example, see the following:

A parametric manipulation of factors affecting task-induced deactivation in functional neuroimaging

Okay, when I try to summarize: The very local inhibiton can never observed (pretty clear when you look at the operating mode of the fMRI). Other inhibitions can take place, but only at certain tasks which demand a kind of attention, like these "differenciation-tasks", I hope you know what I try to say, however it's not a common phenomenon.
My thought was rather like this: You lie in the MRI and you are asked to listen to a complicated structured sentence and later you have to explain the meaning of the sentence. My idea was that you see then on the fMRI-pic an increased activity in the primary, secondary auditory cortex and in Wernicke's area and other related areas, but a decrease in areas which are never related to this kind of task in order to fulfill this task fast and efficient and allocating the limited resources in a better way.
I ask again: Was that kind of decrease ever observed in the fMRI? Or do you think fMRI is improper for that on principle?
I apologize for these, maybe noobish, maybe boring, questions, but I know just the basics of fMRI and have no real clue how accurate it really is. The pics I have seen so far are all these "picture-book " pics where everythings fits and which are very edited, so I have no ideo how much information from the scanning to the pic, which is shown me, is actually lost. Therefore I asked if you have some more explames at the beginning.