The human metathalamus is extremely important for relaying auditory and visual signals to the rest of the brain. However, a detailed, three-dimensional map of the cellular structure of the area was still missing. Using the BigBrain dataset, an integral part of the HBP, the researchers focused on the two distinct parts of the metathalamus: the medial geniculate body (MGB) with its subdivisions; and lateral geniculate body (LGB) with its six layers.