? The spatiotemporal dynamics of human brain activation can be non-invasively imaged by combining functional Magnetic Resonance Imaging (fMRI) with magneto- and electro-encephalography (M/EEG). fMRI locates altered cerebral hemodynamics with good spatial accuracy but poor temporal resolution. Conversely, M/EEG are instantaneous measures of population synaptic activity, but are hard to localize because of spatiotemporal cancellation. Furthermore, the transfer functions from cortical neuronal synaptic currents and cell-firing, to extracranial hemodynamic and electromagnetic signals, are unknown. The potential variability of the relationships of hemodynamic and electromagnetic signals to each other, and to their underlying neural substrates, make it necessary to explore and define these relations in behaving humans. We propose to measure neuronal activity using linear arrays of micro-electrodes. Optical measurements will quantify hemodynamics using cortical point spectroscopy and laser Doppler. Simultaneous measures within the same cortical micro-domain will be made during spontaneous activity, calibration states, and a variety of cognitive tasks. If successful, this research will reveal, at an unprecedented level of quantification and certainty, the relations between hemodynamic and electromagnetic measures, and the underlying activity of neuronal populations, during cognition in humans. ? ?
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