Comparison of learning curves of WT mice from the MWM4 versus the MWM2 protocol. Data show the mean degree of search error ± SEM. The MWM2 protocol is more challenging than the MWM4 protocol for WT and CREB^αδ- deficient mice regardless of age and sex. An example of this protocol difference is shown by WT mice in the MWM2 that exhibit a significantly different learning curve with a greater degree of search error on day two than their counterparts in the MWM4. * p<0.05.

Learning curves of male and female WT and CREB^αδ- deficient mice in the MWM2 protocol split by age. Data show the mean degree of search error ± SEM. Solid lines with squares depict the WT mice. Dotted lines with circles depict the CREB^αδ- deficient mice. Males and Females are designated as M and F, respectively. (A-C) Young and middle-aged male CREB^αδ- deficient mice learned as well as their WT counterparts, but the aged are impaired. Aged male CREB^αδ- deficient mice exhibited a significantly greater degree of search error than their WT counterparts on three of the four test days. (D) In the MWM2, young female CREB^αδ- deficient mice showed a greater degree of search error than their WT counterparts that is approaching significance (p=0.09) on days two and three. (E) and (F) Middle-aged and aged female CREB^αδ- deficient mice were impaired in the MWM2 as shown by a significantly greater degree of search error on two and three of the test days, respectively. * p<0.05.

Number of platform crossings during the probe trial for WT and CREB^αδ- deficient mice in the MWM4 and MWM2 protocols. WT and CREB^αδ- deficient mice are designated as +/+ and -/-, respectively. Young, middle-aged, and aged mice are designated as Y, M, and A, respectively. Males and Females are designated as M and F, respectively. (A) All WT mice from the MWM4 protocol showed a preference for the goal quadrant during the probe trial, as shown by a significantly higher number of crossings over the platform location in the goal quadrant compared to hypothetical platform crossings in the other quadrants, with one exception. The preference for the goal quadrant in aged WT males did not reach significance. (B) In contrast, only young female and middle-aged male CREB^αδ- deficient mice in the MWM4 showed a preference for the goal quadrant during the probe trial. (C) Among WT mice from the harder MWM2, only young and middle-aged male WT mice showed a significant preference for the goal quadrant. (D) None of the CREB^αδ- deficient mice from the MWM2 showed a significant preference for the goal quadrant in the probe trial. * p<0.05, ** p<0.01, *** p<0.001.

Learning curves of male and female WT and CREB^αδ- deficient mice in the MWM4 protocol split by age. Data show the mean degree of search error ± SEM. Solid lines with squares depict the WT mice. Dotted lines with circles depict the CREB^αδ- deficient mice. Males and Females are designated as M and F, respectively. (A-C) Male CREB^αδ- deficient mice of all three ages performed as well as their WT counterparts in the MWM4, with one exception. Middle-aged male CREB^αδ- deficient mice showed an early learning impairment as exhibited by a significantly greater degree of search error on day two. They showed no improvement in the degree of search error from day one to day two, but with more testing they eventually learned to the same extent as their WT counterparts. (D) Young female CREB^αδ- deficient mice performed as well, or better (on day three) as their WT counterparts in the MWM4. (E) Middle-aged female CREB^αδ- deficient mice showed an early learning impairment as exhibited by a significantly greater degree of search error on day two, but with more testing they eventually learned to the same extent as their WT counterparts. (F) Aged female CREB^αδ- deficient mice were impaired as shown by a significantly greater degree of search error than their WT counterparts on test days three and four. * p<0.05.

Sex differences in the extent of learning among CREB^αδ- deficient mice in the MWM4 and MWM2 protocols. Data show the mean degree of search error on test day four ± SEM. WT and CREB^αδ- deficient mice are designated as +/+ and -/-, respectively. Males and Females are designated as M and F, respectively. Young, middle-aged, and aged mice are designated as Y, MA, and A, respectively. (A) WT mice had achieved a similar amount of learning by the fourth MWM4 test day, as exhibited by a lack of significant sex or age differences in the degree of search error. Among CREB^αδ- deficient mice, females but not males showed a clear impairment in the oldest age group, as shown by a significantly greater degree of search error on the fourth MWM4 test day compared to the other mice. (B) In the MWM2, all WT mice showed a similar degree of search error. Among CREB^αδ- deficient mice, females showed a learning deficit at a younger age than the males: middle-aged and aged females, while only aged males exhibited a significantly greater degree of search error. * p<0.05.