Final answer:
Cajal identified unidirectional flow of information in neurons through his observations of the structure of neurons, particularly unipolar cells.
Step-by-step explanation:
Unipolar cells, also known as pseudo-unipolar cells in humans, have a single process emerging from the cell body. Unipolar cells are sensory neurons and their dendrites receive sensory information, sometimes directly from the stimulus itself. Santiago Ramón y Cajal, a Nobel Prize-winner, identified unidirectional flow of information in neurons through his observations of the structure of neurons more than 100 years ago. Cajal noticed that the axon of a unipolar cell splits, with one end having dendrites for receiving sensory information and the other end forming synaptic connections with a target. This observation led him to conclude that the flow of information in neurons is unidirectional