One way to decipher a complex biological problem, such as understanding how the brain works, is by using a simpler system that enables greater experimental or computational access. Hydra is a small, transparent relative of the jellyfish, and represents the first animals to have evolved a nervous system. Correspondingly, the nervous system of Hydra is very simple, with a few hundred neurons forming a net which tiles the body of the animal, without ganglia or brain. In spite of this simplicity, Hydra's nerve net generates a rich range of nimble behaviors, including contracting, elongating, bending, searching and somersaulting. Recently, the investigators of this project developed genetically altered Hydra strains in which the activity of neurons and muscles causes them to generate a light signal. Thus, the investigators can directly observe the activation of every neuron and muscle cells in an animal while it is behaving. Because of this, they can use statistical methods to analyze how neural activity drives movements. They discover basic principles of how simple nervous systems control muscles to produce behaviors. Given that Hydra has no brain, this project may reveal how complex movement can be organized without any central coordination. Further, Hydra has an extraordinary ability to regrow: its cells are constantly being replaced, and a complete Hydra body can reform from even very small pieces of the animal. Understanding how the nerve net of Hydra continues to produce stable behavior in the face of rapid turnover may advance understanding of how nervous systems can repair themselves. The study of Hydra with an integrated imaging/computational approach serves as an appealing platform for outreach opportunities. The research introduces members of the general public to neuroimaging and essential biology and mathematical neuroscience. It also provides training opportunities for researchers at all levels. The Hydra system is deeply integrated into summer courses at the Marine Biological Laboratory and provides cross-cutting projects for students from diverse backgrounds.
This project aims to decipher the relation between the activity of a nervous system, the muscles it controls and the behavior the muscles generate using the cnidarian Hydra. The investigators focus on decoding the neural basis of a few elementary behaviors that can be rigorously identified and that are generated by the endodermal and ectodermal nerve nets. The investigators use calcium imaging of every neuron and every muscle cell in mounted Hydra preparations during contractile behaviors. To analyze the required data sets, the investigators develop algorithms to track cells in the moving, deforming animal and apply dimensionality reduction methods to discover spatiotemporal patterns of movement corresponding to muscle activation patterns. The end product is a quantitative model that explains how contractile behaviors are generated. As another deliverable, the techniques developed to track neurons and discover spatiotemporal patterns are made widely available in an open source platform and may be of use in other systems. This proposed work will help establish Hydra as a model neural system for which a complete accounting of neural activity and behavior may be rigorously approached.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
