Final answer:
The likely explanation for a greater number of neurons correlating with higher performance on the Mental Rotations Test (MRT) is that individuals with higher spatial ability naturally develop more neurons.
Step-by-step explanation:
The question at hand revolves around the relationship between neuron count and performance on the Mental Rotations Test (MRT), which is a standard measure of spatial ability. Looking into the options provided, the most plausible explanation, considering current understanding of neuroscience, would be (a) Individuals with higher spatial ability naturally develop more neurons. This suggests that those with a higher spatial ability might develop more neurons through neural plasticity, which is the brain's ability to change and adapt as a result of experience. It is known that neural connections can be strengthened through repeated use, which could infer that engaging in tasks that require spatial abilities might enhance and increase neural networks over time. However, it's important to note that correlation does not imply causation, and more research would be needed to establish a definitive causative relationship.