Figure 1. Recording from geniculate afferents in the muscimol-silenced cortex.

a. Cortical recordings showing a radial alignment of a single electrode penetration within a cortical orientation domain, determined before application of muscimol. Cortical layers reconstructed from histology are indicated by Roman numerals I-VI (WM: white matter). The preferred orientations of cortical neurons recorded along the course of the electrode penetration are indicated by lines. Muscimol was applied to the surface of the cortex to silence cortical activity, and after two hours, afferent receptive fields were plotted in layer IV between the two letter Ls, which show centers of lesions made at the end of the experiment. b. Four representative vertical penetrations through layer 4, two dominated by off-center afferents (A, B), one dominated by on-center afferents (D) and another one mixed (C). c. Table showing all electrode penetrations, the number of afferents recorded in each (left) and the category assigned to each penetration. d. Map showing the segregation of on- and off-center afferents obtained in two different experiments by making multiple single-electrode penetrations. Left, actual maps, luminance-coded by the fraction of off afferents. Right, identical maps smoothed by a 2-D Gaussian in order to highlight the clustering of penetrations of like type.