Figure 3.

Aging decreases learning-induced spine formation in the motor cortex. (A) In vivo time-lapse imaging of the same dendritic segments over 2 days in the primary motor cortex of young and old mice, with or without motor training. Empty and filled arrowheads indicate individual spines that were eliminated or newly formed, respectively. Scale bar, 2 μm. (B) Percentages of dendritic spines formed over 2 days in young and old mice. (C) Percentages of dendritic spines eliminated over 2 days in young and old mice. (D) The density of dendritic spines on the apical tuft dendrites of L5 pyramidal neurons in young adult and old mice. (E) Rotarod performance in young and old mice (n = 8 mice per group). After 2-day training, old mice showed less performance improvement than young mice (Day 1: t = 2.065; P = 0.0580; Day 2: t = 6.230; P < 0.0001). (F,G) Following 2-day training, animals’ performance on the rotarod strongly correlated with the number of new spines formed but not with the number of spines eliminated (Pearson correlation). Throughout, individual circles represent data from a single mouse. Summary data are presented as mean ± SEM. *P < 0.05, ****P < 0.0001 by two-tailed Mann–Whitney test in panels (B–D) and two-tailed Student’s t-test in panel (E).