Fix It Extensive Evidence Indicates Exercise Improves Hippocampally Mediated Learning and Memory

Fix It
Extensive evidence indicates exercise improves hippocampally mediated learning and memory. Dr. Smith knows that exercise not only increases blood vessel density in the hippocampus, but also increases the rate of neurogenesis in the hippocampus, and wants to know which is involved in the exercise-induced memory improvements. To that end, 30 rats were divided into three groups. Group 1 consisted of males only. Group 2 consisted of females only. Group 3 consisted of males and females. In the first condition rats received a drug to block the formation of new neurons via IV injection. In the second condition rats received a drug to block the formation of new blood vessels via oral administration. In the third condition, which was the control condition, rats received nothing. All animals were permitted to exercise at will for two weeks on a running wheel located in their home cage. Dr. Smith examines how well the rats perform a spatial learning task. He finds that rats in the antineurogenesis condition perform much more poorly on the task than the rats in the anti-angiogenesis and control conditions. Dr. Smith concludes new neurons are important for spatial learning, but new blood vessels are not.
How is this study confounded? Fix it!