Spatial frequency modulates the human visual cortical response to temporal frequency variation: an fMRI study

The brain response to temporal frequencies (TF) has been already reported, but with no study for different TFs with respect to various spatial frequencies (SF). Functional Magnetic Resonance Imaging (fMRI) was performed by 1.5 Tesla General Electric-system in 14 volunteers (9 males and 5 females, range 19–26 years) during square-wave reversal checkerboard visual stimulation with different temporal frequencies of 4, 6, 8 and 10 Hz in two states of low SF of 0.5 and high SF of 8 cpd (cycles/degree). The activation map was created using the data obtained from the block designed fMRI study. Pixels whose correlation coefficient value was above a threshold of 0.33, in significant level P <0.01 were considered activated. The average percentage BOLD (blood oxygenation level dependent) signal change for all activated pixels within the occipital lobe, multiplied by the total number of activated pixels within the occipital lobe, was used as the criterion for the strength of the fMRI signal at each state of TF& SF. The results demonstrated that the strength of the fMRI signal in response to different TFs was maximum in 6Hz for high SF of 8cpd, while it was maximum at TF of 8Hz for low SF of 0.5cpd. The results of this study agree with the results of animal invasive neurophysiological studies showing spatial and temporal frequency selectivity of neurons in visual cortical areas. These results can be useful for vision therapy (such as the treatment of Amblyopia) and selecting visual task in fMRI studies.