The findings also help confirm one of the basic assumptions of functional MRI. The technology measures changes in blood flow to brain cells, which neuroscientists use as a proxy for neural activity. Finding a population of cells that respond specifically to faces within the face-processing region highlighted by MRI "shows that the assumption everyone operates under is correct," says Christof Koch, a neuroscientist at the California Institute of Technology, in Pasadena.

Tsao is now studying the different properties of each face-processing region in more detail. One face patch, for example, appears to be involved in detecting the overall shape of the face. "Our hypothesis is that it measures ratios [between facial features], but that it hasn't made the identity of the face explicit yet," she says. "I think the three anterior regions are encoding other aspects of faces--expression, movement, memory, identity."

To truly understand how the brain processes visual information, scientists must figure out how disparate pieces of information--the shape of the face and a sense of recognition of the face, for example--are bound together to create our perception of the face. Using dyes detectable with MRI to trace connections between different neurons, Tsao will record activity from multiple connected cells to determine how visual information is summed and shaped as it travels through the brain. "I think that seeing how this information is transformed will clarify a lot of what the brain is doing," she says.

Ultimately, Tsao's work could shed light on how neural activity leads to conscious visual perception. "It's a step toward answering the age-old question, how does visual conscious perception arise from the underlying neural activity?" says Koch. "What is the relation between the mind and the brain?"