Vision Research Lab, Center for Brain Science Research, School of Life Sciences, Fudan University, China
Wednesday 4 October 2006, 16:00
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Visual cross-stream modulation of feedback projections from high-order areas to lower-order areas in the visual cortex of the cat
The dorsal stream and the ventral stream are two the major parallel streams carrying and processing distinctly different types of motion and form information along the visual pathways in the cat’s and monkey’ brain. To study the influences of higher-order visual cortical area on the lower-order area in the visual information processing, we examined the influence of signals descending from areas of 21a and the posteromedial lateral suprasylvian (PMLS) in the visual cortex on the orientation and direction selectivity and their functional organization in cat area 17 revealed by intrinsic signal optical imaging combined with local inactivation in 21a and PMLS by GABA or lesion.
A spatial frequency-dependent decrease in response amplitude of orientation maps to grating stimuli was observed in areas 17 and 18 when area 21a in the cat, known as a dominant form-processing region like V4 in the monkey, was inactivated by local injection of GABA, or by a lesion induced by liquid nitrogen freezing. The decrease in response amplitude of orientation maps of areas 17 and 18 after the area 21a inactivation paralleled the normal response without the inactivation. Application in area 21a of bicuculline, a GABAa receptor antagonist caused an increase in responses amplitude of orientation maps of area 17. The results indicate a positive feedback from high-order visual cortical area 21a to lower-order areas, underlying a spatial frequency-dependent mechanism that enhances the global orientation selectivity of lower-order cortex.
The dominant motion-processing region of the PMLS cortex was deactivated by local injection of GABA and the optically recorded orientation/direction maps visually evoked by moving gratings was assayed in area 17. Feedback deactivation of the PMLS significantly decreased signal strength of direction maps and virtually abolished the global layout of direction maps of area 17, however, the basic structure of the orientation maps was preserved. Our data suggest that signals feedback from the PMLS cortex strongly contribute to the emergence of direction, but not orientation selectivity in primary visual cortex.
Overall, our results indicate that higher-order cortical areas along one information processing stream may exert cross-stream modulatory effects on fundamental properties of neurons located in the lower-order areas along another information processing stream.
The work was supported to T. Shou by a grant of the National Natural Science Foundation of China, No.90208013
Collaborators: Luoxiu Huang, Wei Shen, Zhiyin Liang