College of Optometry Faculty Proceedings, Presentations, Posters, Speeches, Lectures, etc.


Effects of RF surround stimulation on the orientation tuning of V1 and V2 neurons



Conference Title

Society of Neuroscience Annual Meeting


Society of Neuroscience


Washington, DC / November 12-16, 2005

Publication Date / Copyright Date



There is considerable debate on how the orientation tuning of individual V1 neurons emerges. Although the alignment of feed-forward geniculate inputs is an important factor, there is enough evidence to support the idea that the sharpening of orientation tuning depends on suppressive and/or facilitatory signals coming from other neurons with similar orientation preference via the intracortical connections and/or the feedback connections from higher order visual areas. In this study we determined whether or not stimulation of RF surrounds, which are known to depend on similar intrinsic and/or long-range connections, improve the orientation selectivity of V1 and V2 neurons. Microelectrode recording experiments were conducted in anesthetized and paralyzed monkeys. After optimizing the spatial frequency and orientation of sine wave gratings (diameter = 4.5°, TF = 3.1 Hz, contrast = 80%) for each unit, we obtained area summation functions to determine the unit's RF center and surround. The orientation/direction tuning functions were obtained for individual V1 and V2 neurons by drifting the gratings in 12 directions over the RF center with or without the RF surround. The orientation selectivity of each unit was determined by using a vector summation method and a traditional method of calculating bandwidths of tuning functions. Surround stimulation significantly improved the orientation tuning for the majority of V1 and V2 units. The magnitude of this improvement was similar in each unit for the two analysis methods employed in this study. These results indicate that the orientation tuning was narrower with surround stimulation primarily because the unit’s responses to non-optimal orientations near the unit’s preferred orientation were suppressed by long-range signals.



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