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Salk scientists map the frontiers of vision

Marina Garrett, Ed Callaway and James Marshel

Marina Garrett, Ed Callaway and James Marshel

To understand the extraordinarily complex computations of the human brain, scientists have mostly relied on studies of primates, our closest relatives in the animal kingdom. Powerful new scientific tools are now emerging, that could allow scientists to complement primate studies by studying the relatively simpler brains of mice.

In a study published in Neuron, a team led by Edward Callaway produced for the first time neuron-by-neuron maps of the regions of the mouse brain that process different kinds of visual information, laying the groundwork for decoding the circuitry of the brain using cutting-edge genetic research techniques only possible in mice.

Although such genetic engineering techniques in mice offer huge potential, little was known about what areas of the mouse visual cortex were responsible for processing different elements of the visual information. To remedy this, Callaway and his colleagues set out to chart a map of the mouse's visual processing system. They first mapped the representations of the mouse's visual field, the area of three-dimensional space visible through its eyes, to identify distinct cortical areas each containing full neuronal "maps" of the visible outside world. They then injected seven of these areas with a calcium-sensitive fluorescent dye that glows when exposed to a certain color of light. The amount of calcium in nerve cells varies depending on the activity level of the neurons, so the scientists could measure the activity of brain cells based on how brightly they glowed. Callaway's team then displayed different visual stimuli on a television monitor and recorded what stimuli were preferred by neurons in each area. They found that each area has a specialized role in processing visual information, such as the direction objects move in space or distinguishing fine detail.

Ultimately, Callaway says, understanding in detail how the mouse brain works will illuminate the workings of the human mind.

"This gives us new ways to explore the neural underpinnings of consciousness and to identify what goes wrong in neural circuits in the case of diseases such as schizophrenia and autism," he says.