Figure 7.

dLGN neurons can detect spatial structure in natural movies presented through closed eyelids. A, Structured movies were identical to the movie stimuli described above (Fig. 1). In unstructured movies, each frame was a structureless blank with luminance equal to the mean luminance of the corresponding frame of the structured movie. Three pairs of structured and unstructured movies were used. B, Rasters show responses of three cells to corresponding structured (top row) and unstructured movies (middle row). Each raster shows spiking activity during the movie period (see Materials and Methods and Fig. 1). Histograms (bottom row) compare structured (s) and unstructured (u) movie responses. All three example cells were deemed structure sensitive. Cell 1, recorded at P26, exhibited a significantly higher firing rate during presentation of the entire structured movie and was, therefore, deemed structure sensitive (Mann-Whitney p < 0.05). Cells 2 and 3, recorded at P29, showed significant differences in their responses to corresponding frames of the structured and unstructured movies (p < 0.05; Dunn post test after Kruskal-Wallis nonparametric ANOVA). Of 44 neonatal dLGN neurons that responded to movies, 28 (64%) were classified as structure sensitive. In the histograms, the asterisks denote bins in which responses differed between the two movie types (p < 0.05; Dunn post test after Kruskal-Wallis ANOVA), and the structure sensitivity index is stated on the left. C, The structure sensitivity index was used to compare the degree to which the responses of different cells were modulated by spatial structure in the movies (higher values indicate greater modulation by spatial structure; see Materials and Methods). The scatter plot shows that during this developmental window, there was a positive, but not statistically significant, correlation between structure sensitivity and age (Spearman r = 0.10; p = 0.55). Other conventions are as shown in Figure 2.