I have just been going through a thought provoking new article by Hughes Duffau (2011), and thought I would provide a brief synopsis of the methods, and highlight a result or two. For those of you who are not very familiar with Direct Electrical Stimulation (DES) work, this would be one of the better places to start, as it is very well written and the reference section covers nearly the entire literature.
The first strength of the paper lies in the methods. Whereas the vast majority of human neuroimaging (MRI, EEG, MEG) attempts to measure cortical activity through the scalp, skull, and meninges, DES goes straight to the source: In patients undergoing brain surgery (awake patients to be specific), bipolar electrode tips deliver biphasic current pulses to the cortex and white matter of the human brain. While the current is being delivered, a patient’s performance on some task is being monitored. When the patient’s performance changes due to the stimulation, you have successfully mapped an “eloquent region.” In other words, that region’s neuronal activity plays a direct role in producing that behaviour.
Dr. Duffau's results using DES support a view of the brain that is very dynamic, and do not adhere to the localization hypothesis. To put it another way, complex human behaviours such as language rely on many different brain regions operating in concert. If one of the regions is damaged, it is possible to re-organize the circuit and preserve the function (as long as the white matter connections are left intact). Bear in mind that this is in relation to so-called frontal/executive functions (cognitive processing, language, emotion, etc), and basic sensory systems might operate far differently (not surprisingly, Dr. Duffau has published on this as well).
Below are a few references... I am including two other intriguing articles for those who want to know more about DES, and how the brain might be wired. As always, email me with any questions or just follow up with a comment.
Duffau H (2011) The “frontal syndrome” revisited: Lessons from electrostimulation mapping studies. Cortex (In Press).
Mandonnet E, Winler PA, Duffau H (2010) Direct electrical stimulation as an input gate into brain functional networks: principles, advantages, and limitations. Acta Neurochirurgica 152: 185-193.
Mandonnet E, Jbabdi S, Taillandier L, Galanaud D, Benali H, Capelle L, Duffau H (2006) Preoperative estimation of residual volume for WHO grade II glioma resected with intraoperative functional mapping. Neuro-Oncology 9: 63-69.
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ReplyDeleteI just wanted to follow up on this post by recommending a brand-new article that just came out in Nature Reviews Neuroscience. It is quite a concise article (i.e., a short read), and promotes a degree of skepticism with respect to DES.
ReplyDeleteBorchers, Himmelbach, Logothesis, and Karnath propose that while DES has many merits (especially in the clinical realm), several uncertainties inherent to the method should preclude it from being viewed as a "gold standard" for cortical mapping (at the moment). In other words, because the physical mechanisms behind DES are not perfectly understood, it ought to be considered another imaging tool in the arsenal... not the only one.
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