In 1489 Leonardo was able to obtain one or more human skulls. He sectioned them to investigate their structure and recorded his findings on the pages of a notebook, three sheets of which are displayed in the centre of the gallery.

Leonardo attempted to infer the paths of the sensory nerves and the form of the brain. He regarded this knowledge as key to some of the topics that he wished to investigate, such as the emotions and the nature of the senses. But without an actual brain to dissect, the skulls alone could not provide that information.

The notebook was therefore to languish, mostly empty, for almost twenty years.