Inverse Inference in fMRI

I attended a nice talk by UCLA's Russel Poldrack yesterday, on the topic of inverse inference in fMRI studies.

A bit of background for those unfamiliar with fMRI: it's a technique which measures oxygenation in the blood via MRI. The idea behind fMRI studies is that we can assign participants a task, which should require them to perform particular cognitive operations, which are going to be at least somewhat localized in the brain, the neurons of which will require more oxygen, depleting the surrounding blood of oxygen, a fact which can be measured by fMRI. So from this we can associate the performance of certain tasks with blood oxygen depletion in particular areas of the brain. And it's not too far of a step to roughly equate blood oxygen depletion with increased neuron activity and thus associate the performance of particular tasks with increased use of particular brain areas.

Now, the inference gets a little fuzzier when we try to map task performance to cognitive operations. So, while we might notice increased activity in a particular area of the brain while a subject is singing a song, it would be an unfounded assertion to say that that area of the brain is responsible for song recall, or song production, or anything that specific. Further evidence can help us narrow in on statements like these, but it's tricky business because of our dim understanding of the brain.

The first half of the talk was about the inverse of these--often illfounded--inferences. That is, the idea that because a certain task or stimulus activates a particular part of the brain, the subject must be undergoing cognitive operations that have been previously associated with that area. Prof. Poldrack used this NY Times article as an example of this type of flawed inverse inference. Here's a good example from that article:

6. In Rudy Giuliani versus Fred Thompson, the latter evokes more empathy.

There is much discussion this year about “authenticity,” as politicians strive to be credible and real. On this front, Mr. Thompson may have an advantage over Mr. Giuliani. When our subjects viewed photos of Mr. Thompson, we saw activity in the superior temporal sulcus and the inferior frontal cortex, both areas involved in empathy. When subjects viewed photos of Mr. Giuliani, these areas were relatively quiet.

Notably, a group of neuroscientists, psychologists, etc., wrote in to complain about the flawed logic in the article. Their letter was published by the NY Times. And apparently the group that conducted this research is a commercial outfit.

The second half of the talk was about establishing an ontology of cognitive processes. Using such an ontology--as well as a centralized database of fMRI data and metadata--Poldrack suggested we might be able to form more conclusive ties between areas in the brain and cognitive processes. He's heading up a project called the Cognitive Atlas, in an effort to form such an ontology in a wiki sort of effort. A few people raised concerns about how accurate a collaborative effort could be, but he suggested that the value would be in reaching either a consensus or well founded competing theories, which could then be tested using machine learning techniques against the previously mentioned fMRI database.

Cheers.