I'm sorry if this question is vague: I don't yet understand stats terminology very well.
Let's say I am interested in a measurement X. Imagine it is neuron diameter. I want to know if brain regions A, and B differ in average neuron diameter. I have 100s of measurements of neuron diameters sampled from regions A and B from different individuals of the same species: animals U, V, and W.
What is an appropriate way to check if the differences between regions A and B are statistically significant? Can I just lump all the individuals together for each region, so I compare 2 distributions? Or is there some multi-level approach that I should do?