Frequency dependence and gender effects in visual cortical regions involved in temporal frequency dependent pattern processing

Neural response to flickering stimuli has been shown to be frequency depend ent in the primary visual cortex. Controversial gender differences in blood oxygen level dependent (BOLD) amplitude upon 6 and 8 Hz visual stimulation have been reported. In order to analyze frequency and gender effects in ea rly visual processing we employed a passive graded task paradigm with a dar tboard stimulus combining eight temporal frequencies from 0 to 22 Hz in one run. Activation maps were calculated within Statistical Parametric Mapping , and BOLD amplitudes were estimated for each frequency within the striate and extrastriate visual cortex. The BOLD amplitude was found to steadily ri se up to 8 Hz in BA 17 and 18 with an activation plateau at higher frequenc ies. In addition, we observed a laterality effect in the striate cortex wit h higher BOLD contrasts in the right hemisphere in men and in women. BOLD r esponse rises similarly in men and women up to 8 Hz but with lower amplitud es in women at 4, 8, and 12 Hz (30% lower). No frequency effect above 1 Hz was found in the extrastriate visual cortex. There was also a regional spec ific gender difference. Men activated more in the right lingual gyrus (BA 1 8) and the right cerebellum compared with women, whereas women showed more activation in the right inferior temporal gyrus (BA 17). The study indicate s that frequency dependent processing at the cortical level is limited to t he striate cortex and may be associated with a more global information proc essing (right hemisphere dominance), particularly in men. The finding of si gnificantly lower BOLD amplitudes in women despite previously shown larger VEP (visual evoked potential) amplitudes might suggest gender 0 differences in cerebral hemodynamics (baseline rCBV, rCBF, or neurovascular coupling). The regional distinction points at additional differences in psychological processing even when using a simple visual stimulus. Hum. Brain Mapping 14 :28-38,2001 (C) 2001 Wiley-Liss, Inc.