CFC performance of 18 month old mice. (a,b) Freezing (seconds) during 3 min of shock-context test (SC-t, black bars) and context-shock test (CS-t, grey bars). C, control; Tr, trisomic. F, female; M, male. Difference between CS-t and SC-t within sex and DS line: ns, not significant. Error bars represent the SEM. Number of animals, SC and CS, respectively (from Table 1): (a) FC, 7,8; FTr, 7.6; MC, 9,6; MTr, 10,11; (b) FC, 10,11; FTr, 10,10; MC, 8,10; MTr, 9,13, (c,d) Freezing during CS-t 30 second intervals for the same sex and DS lines as in (a,b). Filled circles, female control; open circles, female trisomic; filled squares, male controls; open squares, male trisomics. *, significant difference between females and males of corresponding genotypes, p < 0.008–0.04.