Complex sentence: Einstein's corpus callosum was compared to two sample groups: 15 elderly brains and 52 brains Einstein's age (26) in 1905 or his Annus Mirabilis (Miracle Year).
Split into simpler sentences: Einstein's corpus callosum was compared to two sample groups: 15 brains of elderly people and 52 brains from people aged 26. Einstein was 26 in 1905, his Annus Mirabilis (Miracle Year).