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 fMRI signal peaks at a flicker f requency of 8 Hz in human V1, in agreement with previous positron emis sion tomography (PET) and fMRI experiments, The modulation amplitude o f the hemodynamic response to varying continuous periods of flicker st imulation was measured. The hemodynamic response was not observed to b e modulated by neural modulation for periods shorter than 6.7 s. The r esemblance between the BOLD response to the stimulus presentation freq uency and the base-line power spectra at the same frequencies suggests that the same underlying mechanism could be responsible for both curv es and that the base-line fMRI power spectrum is probably due to base- line electrical activity in the brain, The integrals of the resting ba se-line power spectrum, the background power spectrum, the respiration component, and the cardiac component were found to be linearly depend ent on TE.