The zebrafish (Danio rerio) has been used by researchers as a model organism for human disease for decades. In recent years, however, the zebrafish has gained considerable...

More than 30 years after the adult nervous system and cell lineage of the roundworm Caenorhabditis elegans were first mapped,¹ that map of neuron connectivity (i.e., the connectome) still enables scientists to better understand diverse neurobiological mechanisms. Today, C. elegans remains a widely used model for neuroscience research because of its short life cycle, transparent body, and homology to human genes expressed in neurodevelopment.

Alzheimer’s disease (AD) affects more than 5.5 million Americans per year. The earliest symptoms of AD, however, often occur after decades of undetectable damage to the intricate synaptic connections within the brain. Many mechanisms of the disease’s progression remain a mystery for researchers, and effective therapeutics for AD have not been developed yet.

For more than 50 years, scientists have used the roundworm Caenorhabditis elegans (C. elegans)—a hermaphroditic nematode that is widely recognized as an important tool for genetics, cell biology, and neuroscience research. The entire adult nervous system and cell lineage of C. elegans was mapped in 19861 and since then, scientists have used this map of neuron connectivity to help elucidate diverse neurobiological mechanisms. Compared to the 100 billion neurons in the human brain, C.