When ferrets watch the mind-bending movie The Matrix, brain activity is only slightly higher than when they stare at nothing. Scientists say this might mean something about how much of your brain is in use.
Ferret brain activity increased just 20 percent when looking at Keanu Reeves compared to looking at darkness, the study found.
When the lights were turned off, researchers expected that the activity would drop to zero, except for some random, "spontaneous" firing of neurons, explained study leader Michael Weliky from the University of Rochester. A brain region devoted to vision continued idling at 80 percent of full capacity.
Weliky likens this constant high level of activity to a radio station's carrier signal. "The [20 percent] riding on top of that is reality," he said.
At least for ferrets. But even in humans, it is known from electroencephalogram (EEG) readings that the brain is humming along even in sleep. Weliky and his colleagues were interested in the "microstucture" of the brain's spontaneous activity.
As described in a recent article in the journal Nature, they implanted electrodes along a stretch of the visual cortex in 10 ferrets of various ages. "The visual cortex is the first input stage of the brain for visual sensation," Weliky explained.
The electrodes recorded the brain activity in small clusters of 10 to 50 neurons - a precision not capable with an EEG. By showing the ferrets movie scenes, as well as random static and darkness, the research team was able to compare the change in the timing and spacing of neuron firings in response to visual input.
They found patterns in the neuron firings for adult ferrets that were largely missing in infant ferrets. Like human infants, the visual systems of infant ferrets are immature - their eyes do not track moving objects.
The researchers attributed the adult brain patterns to the development of visual perception. Interestingly, the majority of the patterns did not depend on the visual input.
"This actually makes sense," Weliky said. "The biggest part of perception is taking cues from the outside world and passing them through our recollection."
Weliky pondered the philosophical implications of having 80 percent of perception locked in our heads. This helps explain the film choice.
"The Matrix touched on issues of perception that we are working on," Weliky said. "It is a metaphor for questions about the nature of reality."