This confocal microscope image depicts a human neuronal organoid — a minute assembly of human brain cells — growing on a patterned substrate. The axons (green and yellow strands), which conduct electrical impulses throughout the body, primarily grow within the dark channels, avoiding boundaries established by an inhibitory protein (red stripes). At top, beyond the guidance of the protein stripe pattern, the axons extend randomly.

The image was produced by Timothy Catlett, who graduated in 2019 with a PhD in cellular and molecular biology, and Timothy Gomez, a professor of neuroscience in the UW School of Medicine and Public Health, as part of a study testing the effects of autism-causing mutations on axon growth and guidance. It also appeared in the Spring 2022 issue of Grow magazine. Another image from the study was selected as a winner of UW’s Cool Science Image Contest.