Brain development and aging. The brain is a complex organ -- a network of nerve cells, or neurons, producing thought, memory, action, and feeling. How does this complex system change from childhood to adulthood to late life in order to maintain optimal behavioral responses? These questions were put to the test by psychologists who studied hundreds of fMRI brain scans, from two separate datasets, to see how the variability of brain signals changes or remains the same during a human lifespan. Source 5v.