BY EAVESDROPPING on neurons in the brains of cats, scientists have made
videos of what the cats actually see. It confirms that scientists鈥� understanding
of the language of certain visual neurons is bang on target.
Most neuroscientists study vision from the way neurons respond to different
images. This strategy has provided the foundations of our understanding of
perception. But the ultimate test is to apply the opposite approach鈥攖o
reconstruct videos of the ouside world from measurements of the neurons鈥�
behaviour.
To do this, Yang Dan and her colleagues from the University of California at
Berkeley anaesthetised cats and used electrodes to measure the activity of 177
neurons in their lateral geniculate nuclei鈥攖he first stop in the brain for
incoming signals from the eyes. The cats were shown pictures such as the view
from a camera panning across a forest.
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The team reconstructed scenes the cats saw from measurements of neuron
activity, via mathematical equations describing the responses of each cell and
their interactions with other cells. Results from earlier studies suggested 20
to 30 neurons respond to each point in the field of vision. And sure enough, the
reconstructed scenes were clearest when each point was recreated from a similar
number of neurons (The Journal of Neuroscience, vol 19, p 8036).
鈥淭he majority of what we know about vision has been determined by looking at
what a single neuron does,鈥� says team leader Garrett Stanley of Harvard
University. 鈥淭his work looks at groups of neurons and how they might encode
information about the outside world.鈥�
Ehud Kaplan, a neuroscientist at the Mount Sinai School of Medicine in New
York, says the experiment is technically impressive. 鈥淭hey crossed all the t鈥檚
and dotted all the i鈥檚.鈥� He hopes that future studies will shed light on how the
brain makes sense of these scenes. 鈥淥ur ultimate goal is to comprehend how we
understand the world, how we know that this is grandmother and the other is
Marilyn Monroe.鈥�