Plasticity of the contralateral pathway in the binocular zone. A: strength of cortical response after each manipulation. The strength is measured as the average pixel value at each threshold. The strength at threshold 1 is the peak pixel value; the strength at threshold 0.5, for example, is the average strength of each pixel whose magnitude is >50% of the peak pixel value. Each line is the average across all mice in that group. The numbers of mice in each group are reported below, and in each figure legend hereafter. Error bars are omitted for clarity but are presented as SD at 0.4 threshold in C. B: example magnitude maps from contralateral eye visual stimulation in each paradigm. Abbreviations in the upper right of each image are as in Fig. 1. Scale bar is 500 μm. C: mean ± SD of the response magnitude for each condition measured at the 60% threshold (0.4 in A). P values for the appropriate comparisons are presented in the text. D: mean ± SD of the response area in square millimeters. P values for the appropriate comparisons are presented in the text. ND, n = 8; cMD, n = 8; BD, n = 9; iMD, n = 8.

Plasticity of the ipsilateral pathway in the binocular zone. A: strength of cortical response after each manipulation. Graph is as in Fig. 2A. The number of mice in each group is given below. B, E, and H: example ipsilateral eye magnitude maps from each visual manipulation. Abbreviations in the upper right of each image are defined below. Scale bar is 500 μm. C and F: mean ± SD of the response magnitude for each condition measured at the 60% threshold (0.4 in A). *, significance. P values for the appropriate comparisons are presented in the text. D and G: mean ± SD of the response area in square millimeters. *, significance. P values for the appropriate comparisons are presented in the text. ND, n = 8; cMD, n = 8; BD, n = 9; iMD, n = 9; cE, n = 6, cE+iMD, n = 8.

Effect of monocular deprivation on contralateral eye maps –examination of all orientations with a spatial frequency cutoff of 0.04 cycle/°. A: representative visual stimulus over 4 s period. Mice viewed a contrast-modulated stochastic noise stimulus. B: example magnitude maps from contralateral eye visual stimulation using the contrast-modulated stochastic noise stimulus. Abbreviations in the upper right of each image are as in Fig. 1. Scale bar is 500 μm. C: mean ± SD of the response magnitude for deprived and nondeprived mice. Note the significant decay in cortical responsiveness following prolonged deprivation. ND, n = 5; cMD, n = 5.

Experimental overview. A: schematic of the mouse visual system. The medial, monocular portion of primary visual cortex receives input solely from the contralateral eye. The lateral, binocular zone receives input from both eyes and maps the central 30° of visual space. B: illustration of the stimulus used to map binocular visual cortex. Mice viewed a drifting bar of light subtending 20° in the center of their visual field. For each mouse, an image of cortical vasculature was acquired and then maps of magnitude and phase were generated. The magnitude map shows the strength and area of responsiveness. Its scale bar indicates change in reflectance over baseline reflectance (ΔR/R). The phase map shows isoelevation retinotopy. The color scale next to the monitor and the coloration of the phase map indicate the vertical position of the stimulus, and the area of cortex responding to each position, respectively. C: summary of experimental manipulations. In all mice, the right hemisphere was imaged. Deprived eyes are 50% gray instead of black to emphasize residual light impinging on the retina (see Fig. 5). All manipulations began on postnatal day 28, the age of peak sensitivity to monocular deprivation. Mice were imaged following 2 wk of altered visual experience. ND, nondeprived; BD, binocular deprivation; cMD, contralateral monocular deprivation; iMD, ipsilateral monocular deprivation; cE, contralateral enucleation; cE+iMD, contralateral enucleation and ipsilateral monocular deprivation.

Deprivation degrades the strength of monocular zone maps. A: example maps of the monocular zone from a nondeprived mouse (left) and a mouse that experienced 2 wk of vision through a sutured eyelid (right). Scale bar is 500 μm. B: plot of average responsiveness at all thresholds for nondeprived and deprived mice. Error bars are SD. *, significance at P < 0.02. ND, n = 6; D (deprived), n = 6.

How lid suture affects the cortical response to visual stimulation. A: the strength of evoked cortical responses before and after lid suture. Four mice viewed a drifting full-screen bar through the contralateral eye. The eyelids were then sutured and another set of maps was acquired using the same stimulus. Finally, the mouse was imaged with no stimulus to establish a noise floor. The range of this baseline noise is indicated by the gray horizontal bar. In these experiments, cortical response was measured as the peak pixel value within a user-defined region of interest. Due to a small number of random, high-intensity pixels in the no stimulus maps, the horizontal bar slightly overestimates the noise level. Lid suture attenuates cortical responsiveness by a mean of 63%. For comparison, we conducted another set of experiments in which mice viewed a similar bar at 5% contrast through open contralateral eyes. Notably, these mice had cortical responses that were roughly half as strong as those produced by 100% contrast bars through sutured lids. B: magnitude and phase maps after each imaging condition. The 1st 3 sets of maps are from the same mouse. Open eye magnitude maps show a robust, clearly defined area of cortical responsiveness. Open eye phase maps show smooth, continuous phase transitions, indicating the eye's discrimination of fine differences in stimulus bar elevation. After lid suture, the strength of magnitude maps diminishes, but an area of responsiveness is still evident. The more dramatic effect of lid suture is the loss of spatial resolution, evident in the phase maps. Note the complete absence of retinotopic organization. Instead, large areas of coherent phase likely represent areas of cortex co-activated by diffuse retinal illumination. Magnitude maps generated without a stimulus reveal no area of response while phase maps show no organization. Phase maps from a mouse viewing a 5% contrast bar are almost as well organized as those generated from a 100% contrast bar although the responsiveness is diminished. Scale bars are 500 μm.