After excluding experiments in which the age of the animal was not stated the mature group had the largest (2.14 SMD, 95% CI, 0.91 to 3.37) and the adult group had the smallest (1.66 SMD, 95% CI, 1.06 to 2.25: χ2 for difference = 304.26, Τ2 = 1.07, I2 = 81.9%, d.f. = 55, p<0.0005) change in the cognition-related NBS (Fig 3A).