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Amplitude response and stimulus presentation frequency response of human primary visual cortex using BOLD EPI at 4 T

Detailed measurement of the neural response to flicker frequency using functional MRI (fMRI) were made. The fMRl signal peaks at a flicker frequency of 8 Hz in human V1, in agreement with previous positron emission tomography (PET) and fMRl experiments. The modulation amplitude of the hemodynamic response to varying continuous periods of flicker stimulation was measured. The hemodynamic response was not observed to be modulated by neural modulation for periods shorter than 6.7 s. The resemblance between the BOLD response to the stimulus presentation frequency and the base‐line power spectra at the same frequencies suggests that the same underlying mechanism could be responsible for both curves and that the base‐line fMRl power spectrum is probably due to base‐line electrical activity in the brain. The integrals of the resting base‐line power spectrum, the background power spectrum, the respiration component, and the cardiac component were found to be linearly dependent on TE.