Defect in MD-induced expansion of nondeprived eye response territory in Ts65Dn mice. A–D, Coronal sections of the visual cortex demonstrating the pattern of Arc mRNA induction following stimulation of the ipsilateral eye in nontrisomic (A, C) and Ts65Dn (B, D) mice. In normally-reared mice, nontrisomic (A) and Ts65Dn (B) responses are similar. Following 4–6 d (from P27–P29 to P31–P35) of MD, nontrisomic mice demonstrate the expected expansion in width of the domain responsive to the nondeprived eye (C). Ts65Dn mice do not demonstrate this expansion (D). E, Quantitation of results. Arrowheads denote medial and lateral edges of responsive domains. Cortical layers are labeled in B. Error bars denote SD. Scale bar, 500 μm; ***p < 1.24 × 10−6; n.s., not significant; t test. Two-way ANOVA for interaction between genotype and MD, p < 0.0001.