The blind, the lame, and the poor signals of brain function--a comment on Sirotin and Das (2009).
Last year, a study appeared that questioned the generally held assumption of a generic coupling between electrical and hemodynamic signs of neural activity (Sirotin and Das, 2009). Although the findings of that study can barely surprise the specialists in the field, it has caused a considerable confusion in the nonspecialist community due to the unwarranted claim of having discovered a "hitherto unknown signal." According to this claim, functional magnetic resonance imaging (fMRI) would pick up not only signals that reflect electrical brain activity but also purely hemodynamic signals that are not linked to neural activity. Here, we show that that study's failure to obtain significant electrophysiological responses to task structure is easily understood on the basis of findings reported for related functional paradigms. Ironically and counter its intention, the study by Sirotin and Das reminds us of the exquisite sensitivity of spatially pooled hemodynamic signals and the limitations of recording only very local samples of electrical activity by microelectrodes. We suggest that this sensitivity of hemodynamic signals should be converted into spatial resolution. In other words, hemodynamic signals should be used to create maps. Further, we suggest that electrical recordings should be obtained at systematically varying functional positions across these maps. And we speculate that under such appropriate experimental and analytical circumstances correspondence between the two modalities would be retrieved-at the expense of a novel signal lost in oblivion.
Kleinschmidt
Andreas
A
INSERM Unité 562, 91190 Gif sur Yvette, France. andreas.kleinschmidt@cea.fr
Müller
Notger G
NG
D001921:Brain / Q000098:blood supply* / Q000502:physiology*; D001931:Brain Mapping / Q000379:methods*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging