Why are standard medical MRIs less useful in neuroscience than FMRIs?

Listen to part of a lecture in a psychology class.
P: Today, I want to talk about the application of FMRIs for studying personality. FMRIs produce images of the brain while it’s processing information or stimuli. I guess you are familiar with MRI, which is a medical imaging technique used for diagnostic purposes. However, FMRIs are mainly used in the research world. Standard medical MRIs only visualize internal brain structures, but FMRIs show what’s actually happening inside the brain. They tell a story of how the brain is actually functioning at a given time. That makes FMRIs a more useful research tool than medical MRIs.
    As for how FMRIs work, well, basically, they use magnetic fields to measure brain activity in different parts by detecting associated changes in blood flow and oxygen levels. So in a sense, this information allows you to produce detailed pictures of the brain, a map with different parts of the brain, with different actions or emotions, or even thoughts.
    And now, by using this technology, psychologists have been seeking for answers for some questions about human personality. Personality is a set of psychological characteristics that remain stable over time. The questions were about, for example, the types of personality and the existence of itself. Does this sound familiar to anyone?
S: Well, as for those questions you’ve mentioned, I read the chapter and it says that questionnaires aren’t very reliable.
P: Right, well, there are some weaknesses using psychological questionnaires. After all, the information conducted from questionnaires can be inaccurate. That’s simply because they rely on what people say about themselves. And that can be subjective with lots of influences caused by many extraneous factors such as memory, or desire to present themselves in the best possible light. So, questionnaires can be somewhat unreliable. But you cannot neglect them entirely. I mean, questionnaires and other traditional methods are still relevant today. Isn’t that right, Paula?
S: Yes, but from what I read, FMRIs study seemed really good on the amygdala study?
P: Well, yes, let’s talk about that. The amygdala study done with FMRIs had its conclusion well supported. The amygdala, so named because it resembles an almond, is a set of nuclei in the brain, and it’s responsible for regulating the emotions of fear and anxiety. You might recall, in this study, subjects were shown pictures of angry, and fearful faces, and the researchers examined how their brain responded to it. Well, in some of the subjects, the amygdala was activated when they saw the picture. You could see changes in the FMRIs. On the other hand, in other subjects, there were no changes observed.
    And then, what’s interesting was a year later, the same group of people was tested again with the same procedure, and their responses remained the same. For people whose amygdala lit up the first time, it lit up again a year later. What this study suggests is that the reaction to fearful stimuli, one aspect of personality, is stable over time. So it might be a partial counterargument to the claim that personality does not remain stable over time.
S: So what about other FMRIs studies? Are there any other potential problems?
P: Well, in general, a lot of people misunderstand personality neuroscience with the surge of excitement. The problem is over-interpretation. Researchers who use FMRIs place significance on where there aren’t any really. I think our brains are incredibly complicated, you know? Measuring blood flow can’t possibly tell you about the sophisticated processes at the neurobiological level.
S: What about those brain maps in our book? Does anyone remember which part of the brain is associated with various thoughts?
P: I have to say how I see it. The brain maps you get from the FMRIs studies are like ... sort of... geographical maps. They’re useful, but you cannot get everything out of it. They’re limited. They’re not going to tell you much about the people of the country, for instance. The same goes for brain maps. That’s how you heighten activity in a region of the brain. But they don’t tell you, for example, why people behave as they do. Therefore, you still need the support of traditional research methods. So, you shouldn’t throw those away and take them into account.