Digital SAT Reading and Writing Practice Question #783

In a neurobiological experiment investigating memory consolidation, laboratory mice were trained to navigate a complex spatial maze. Immediately afterward, half the mice received a dose of a novel compound known to completely inhibit the synthesis of CREB, a protein universally acknowledged as critical for forming long-term memories. The other half received a harmless saline placebo. When both groups were placed back in the maze 48 hours later, the CREB-inhibited mice demonstrated severe navigational deficits compared to the placebo group. Curiously, when researchers repeated the exact same training and injection protocol on a new cohort of mice, but tested their recall only 2 hours after training, both the CREB-inhibited group and the placebo group navigated the maze with equal, high proficiency. Which conclusion is most strongly supported by the results of the experiment?