Neurophysiological investigation of the basis of the fMRI signal

N. K. Logothetis, J. Pauls, M. Augath, T. Trinath, A. Oeltermann

    Research output: Contribution to journalArticlepeer-review


    Functional magnetic resonance imaging (fMRI) is widely used to study the operational organization of the human brain, but the exact relationship between the measured fMRI signal and the underlying neural activity is unclear. Here we present simultaneous intracortical recordings of neural signals and fMRI responses. We compared local field potentials (LFPs), single- and multi-unit spiking activity with highly spatio-temporally resolved blood-oxygen-level-dependent (BOLD) fMRI responses from the visual cortex of monkeys. The largest magnitude changes were observed in LFPs, which at recording sites characterized by transient responses were the only signal that significantly correlated with the haemodynamic response. Linear systems analysis on a trial-by-trial basis showed that the impulse response of the neurovascular system is both animal- and site-specific, and that LFPs yield a better estimate of BOLD responses than the multi-unit responses. These findings suggest that the BOLD contrast mechanism reflects the input and intracortical processing of a given area rather than its spiking output.
    Original languageEnglish
    Pages (from-to)150-157
    Number of pages7
    Issue number6843
    Publication statusPublished - 12 Jul 2001


    • Action Potentials
    • Animals
    • Contrast Sensitivity
    • Electrodes
    • Electrophysiology
    • Hemodynamic Processes
    • Macaca mulatta
    • Magnetic Resonance Imaging
    • physiology: Neurons
    • blood: Oxygen
    • Photic Stimulation
    • Signal Processing, Computer-Assisted
    • Synaptic Transmission
    • physiology: Visual Cortex


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