Gender differences in color processing in mice as revealed with functional PET

OBJECTIVES: Color processing is a central component of mammalian vision. Noninvasive functional transcranial Doppler ultrasound has recently revealed gender-related differences of color processing which include right hemisphere pattern for Blue/Yellow chromatic opponency by men while a left hemisphere pattern was found for women. In the present study, 18F-FDG was used to investigate a similar paradigm in mice with functional PET.
METHODS: Ten anaesthetized CD-1 mice were repeatedly injected on different days with 12 MBq 18F-FDG and subjected in random order to separate monocular stimulation of the left and right eye with white, blue and yellow lights, respectively, for 20 min. A gelatin-(Wratten)-filters-containing chromatoscope was specially designed for that purpose. Subsequently a whole body T1 weighted MR (gradient echo sequence) was performed for anatomical orientation. The SUV of 18F-FDG was determined at 27.5, 32.5, 37.5 and 42.5 min p.i. in the whole cortex and in the left and right visual cortex. Data were analyzed with MANOVA and t-test.
RESULTS: Male mice have significantly higher SUV than female mice in the cortical area, right and left visual cortex in dark baseline condition and during stimulation with white, blue and yellow lights through the right eye but not left (Table). In male mice, the change in SUV was responsive to Blue/Yellow pairs, while in female mice, the response was only to Blue. In male mice, the SUV was highest during Blue stimulation in the left visual cortex through the right eye compared to right visual cortex. Similarly, the SUV was highest during Yellow stimulation in the left visual cortex through the right eye compared to the right visual cortex. Conversely, in female mice, the SUV was highest during Blue stimulation in the right visual cortex through the left eye compared to left visual cortex (Figure). In female mice, there was no change during stimulation with Yellow.
CONCLUSION: The observation in mice is opposite to that in humans where right hemisphere cognitive style for Blue/Yellow opponency was found in men, but a left hemisphere style in women. It is postulated, that the ontogenetic and phylogenetic evolutionary trends for cerebral dominance for color underwent a change during mammalian evolution to humans, perhaps related to left hemisphere dominance for language in most subjects.