Last year he wrote a review for Nature entitled “What we can do and what we cannot do with fMRI” which should be required reading for anyone interested in the technology.

http://www.nature.com/nature/journal/v453/n7197/full/nature06976.html

Having discussed the current state of fMRI technology in detail, including the contribution of electrophysiological and fMRI experiments in animals to our ability to interperet fMRI data, Prof. Logothetis concludes that:

“This having been said, and despite its shortcomings, fMRI is currently the best tool we have for gaining insights into brain function and formulating interesting and eventually testable hypotheses, even though the plausibility of these hypotheses critically depends on used magnetic resonance technology, experimental protocol, statistical analysis and insightful modelling. Theories on the brain’s functional organization (not just modelling of data) will probably be the best strategy for optimizing all of the above. Hypotheses formulated on the basis of fMRI experiments are unlikely to be analytically tested with fMRI itself in terms of neural mechanisms, and this is unlikely to change any time in the near future.

Of course, fMRI is not the only methodology that has clear and serious limitations. Electrical measurements of brain activity, including invasive techniques with single or multiple electrodes, also fall short of affording real answers about network activity. Single-unit recordings and firing rates are better suited to the study of cellular properties than of neuronal assemblies, and field potentials share much of the ambiguity discussed in the context of the fMRI signal. None of the above techniques is a substitute for the others. Today, a multimodal approach is more necessary than ever for the study of the brain’s function and dysfunction. Such an approach must include further improvements to MRI technology and its combination with other non-invasive techniques that directly assess the brain’s electrical activity, but it also requires a profound understanding of the neural basis of haemodynamic responses and a tight coupling of human and animal experimentation that will allow us to fathom the homologies between humans and other primates that are amenable to invasive electrophysiological and pharmacological testing. Claims that computational methods and non-invasive neuroimaging (that is, excluding animal experimentation) should be sufficient to understand brain function and disorders are, in my opinion, naive and utterly incorrect. If we really wish to understand how our brain functions, we cannot afford to discard any relevant methodology, much less one providing direct information from the actual neural elements that underlie all our cognitive capacities.”

And that’s the key thing to remember, it is not a case of either non-invasive studies in humans or electrophysiological studies in animals, both (and more) are necessary if we are to understand how the brain works, what happens when it is damaged or diseased, and what we can do to help.

p.s For those wishing to know more Dario wrote an excelent introduction to this topic a few months ago http://speakingofresearch.com/2009/07/31/the-limits-of-fmri/