In pixels and in health: Computer modeling pushes the threshold of medical research

Instead, each immune cell is a computer simulation, programmed to fight virtual tuberculosis bacteria on a square of simulated lung tissue. In their computer-generated environment, these warrior cells spontaneously build a structure similar to the granulomas that medical I researchers have noted in human lungs fighting tuberculosis. The simulation, created by Denise Kirschner of the University of Michigan in Ann Arbor. is an examnle of an emerging technique called agent-based modeling. This newtool in the world of medical research relies on computing power instead of tissues and test tubes. A growing cadre of researchers, including Kirschner, predicts that agent-based modeling will usher in a broadened understanding of complex interactions within the human body. The agents in the models are individual players-immune cells in the tuberculosis example. Each player is programmed with rules that govern its behavior. Computersavvy researchers then set the agents free to cooperate with, compete with, or kill each other. Meanwhile, the agents must navimate the suirrmindinjv environmpnt. whose properties can vary over space and time. Scientists can manipulate disease progression within the models by changing the agents or their environment and then watching what happens. As opposed to traditional, biologically based in vivo or in vitro experiments, these computer trials are dubbed "in silico." The results can suggest biological experiments to test the models'findings and may eventually lead to new medical treatments. Even simple rules assigned to agents can give rise to surprisingly complex behaviors. When many independent agents interact, they create phenomena-such as the granulomas-that can't necessarily be predicted by breaking down the system into its separate components, says complex-systems specialist John Holland of the University of Michigan. You've got to study the interactions as ~~.* X Z . well as the parts," Holland says. In-silico modeling differs from traditional mathematical modeling, which uses differential equations to understand how molecules or cells behave in an averaged, continuous way. Instead, the agents of in-silico modeling make independent decisions in response to situations that