Özet:
The aim of this study is to investigate the effects of different stimulation frequencies on post stimulus undershoot of the blood oxygen level dependent functional magnetic resonance imaging signal. A fiber optic light delivery system connected to a black opaque sunglass is constructed to deliver visual stimuli to subjects during fMRI scans. One static visual stimulus and eleven flashing stimuli with frequencies ranging from 4 to14Hz and 30 to 46Hz are applied one subject in one fMRI scan session. The acquired data is analysed to obtain the BOLD fMRI parameters. Positive blood oxygen level dependent and post stimulus undershoot signal changes in the primary visual cortex are determined for each frequency. The results suggest that the post stimulus undershoot has a frequency dependency independent of cerebral blood volume changes. Requirement of more data and additional measures for following possibly related phenomena such as cerebral blood flow are discussed which might be investigated in further studies.|Keywords: fMRI, BOLD, PSU, visual cortex.
