Distinguished Lecture Series: “Has brain imaging discovered anything new?”
Speaker Richard E. Passingham (Oxford)
Date 22 March 2012, 18:30
Berlin School of Mind and Brain
Luisenstraße 56, Haus 1
Festsaal, 2nd floor
Contact Annette Winkelmann
The basis for PET was established in 1975 and for fMRI in 1993, and there have now been 293.489 papers using fMRI. Yet it is not clear that the way in which we view the brain has been changed in any fundamental way. Of course, we can image the human brain while people imagine objects or while they judge whether they are or are not perceptually aware, and we cannot do that with animals. But what new principles have been established? By fundamental principle I mean, for example, the principle of hierarchical processing within the visual system. It is true that one can use fMRI to show this, but we already knew it from anatomical and physiological experiments in animals.
One candidate for a new principle comes out of the work on the so called ‘default system’. Areas in this system covary in their activity in the resting state, and this is also true for areas in other anatomical systems. I will take this as my starting point, and go on to show that area A covaries with area B during task 1 but with area C during task 2. I will demonstrate that this is not an artefact of the increase in activity in areas A and B during task 1 and in areas A and C during task 2. I will also show that area A needs to covary with areas B or C in a task-dependent manner to be effective. Finally I will demonstrate that the covariance reflects the influence of area A on areas B or C. The underlying mechanism for that influence is probably the coherence in phase between the oscillation of cell activity in the two areas.
There could be two objections. The first is that the principle has to hold because it is not possible for circuits for task 1 to be active at the same time as circuits for task 2 if the two tasks are mutually incompatible. But that does not mean that it is not important to study the mechanisms. The second objection is that one could demonstrate the principle in experiments on animals. However, the advantage of brain imaging is that it is a whole brain method, and this makes it feasible to study long distance interactions between a variety of areas.