Cat Orientation Plasticity Figure 3. Comparison of orientation selectivity before and after GR. (a): single-orientation maps representing responses to 0u and 90u, constructed at P28 in a normally reared kitten (NR) and at P38 immediately after 1-week vertical-GR in the same animal (1-w GR). Darkness in the maps indicates the strength of responses to stimulus orientations. Horizontal lines drawn inside functionally defined area 17 are superimposed on the maps and placed on the corresponding cortical position. Length of the lines, 7.2 mm. (b): profiles of response strengths for 0u before and after GR along the horizontal lines (blue: before; red: after). (c): those for 90u. (d): profiles of changes in response strengths through GR (differences between the two curves in b and c). Orange: 90u; sky blue: 0u. We carefully calibrated the baseline level of responses so that the response strength averaged over the range of the 2.4-mm extension of the horizontal lines into functionally defined area 18, either before or after GR. Stimulus gratings of a 0.5 c.p.d. spatial frequency presently used do not evoke area 18 (see Materials and Methods). doi:10.1371/journal.pone.0005380.g003 Figure 4. Sensitivity profiles for orientation plasticity. Ordinate: orientation sensitivity defined by (x-y)/(1-y), where x represents the relative size of cortical domains for the exposed orientation in a goggle- reared kitten, and y represents the value of the smoothed curves for normal kittens (Fig. 1g) for the same orientation. Red dots: vertical orientation; blue squares: horizontal orientation. Abscissa: postnatal day of 2-week GR onset. doi:10.1371/journal.pone.0005380.g004 Orientation selectivity modification under short- and long-term GR In Fig. 7, we illustrate how the once-induced over-representa- tion of the exposed orientation changes afterwards. On the left half of the diagram, the normalized relative sizes of cortical domains representing exposed vertical (circles) or horizontal (squares) orientations are plotted at the end of 2-week GR (solid symbols) and also at the end of the succeeding normal rearing (hollow symbols), respectively. Plotted points for identical kittens are linked by the lines. In 4 kittens for which 2-week GR started at P29, 32, 37 and 39, 3-day normal vision immediately before the second optical imaging eliminated the over-representation; the normal- ized relative domain sizes returned to 0 (level of normal kittens). However, in 4 kittens in which 2-week GR started relatively earlier at P16, P21 and P25, recovery during the succeeding 3-days of normal vision was partial. On the right half of the diagram, triangles plot for 4–6 week GR. In 4 kittens with long-term vertical GR started at P21–P25 (triangles), the over-representation of the exposed orientation was retained at moderate levels between 0.39 and 0.64 in the first optical imaging. As tested in two of these kittens (P24–P73; P25– P74), the over-representation was preserved even after 3 weeks of normal rearing. A similar tendency was observed in another kitten in which horizontal GR started at P23 and switched to normal rearing at P51. To summarize, recovery of GR-induced changes are time-dependent in threefold: 1) when 2-week GR covers the relatively late phase of the critical period (at P29–39), normal rearing quickly eliminates the over-representation; 2) when 2-week GR covers the relatively early phase of the critical period (earlier than P29), the diminution of the over-representation is moderate; and 3) GR for 4 weeks or more outlasting the critical period acts to PLoS ONE | www.plosone.org 4 April 2009 | Volume 4 | Issue 4 | e5380