Functional magnetic resonance (fMRI) imaging provides a powerful, non-invasive window on brain function. Blood oxygen-level depletion (BOLD) fMRI tracks changes in neural activity by measuring the decrease in deoxyhemoglobin, corresponding to gradually increased blood flow to active regions. The limited spatial resolution of this technique has prevented analysis of activity within the neural columns that provide the functional architecture of much of the cerebral cortex. Greater fMRI resolution can be obtained by measuring a highly localized, transient increase in deoxyhemoglobin corresponding to rapid oxygen uptake by active cells, but the correlation of this signal with neural activity has been in doubt. In the 14 February Science, Jeffrey K. Thompson and colleagues at the University of California, Berkeley, US, show that this signal does tightly correlate with neuronal firing activity, enabling sub-column analysis of brain function (Science 299:1070-1072, February 14, 2003).

Thompson et al. performed simultaneous recording...

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