New research funded by the National Institutes of Health shows that people can manipulate complex visual images on a computer screen using only the mind.
The study found that when research subjects had their brains connected to a computer displaying two merged images, they could force the computer to display one of the images and discard the other.
The process was controlled by just four brain cells.
"The subjects were able to use their thoughts to override the images they saw on the computer screen," said the study's lead author, Itzhak Fried, of the University of California, Los Angeles.
Previous experiments have shown that it's possible to control a computer cursor with just a few brain cells. However, the task here was more complex, and might have been expected to involve cells in the various brain areas needed for vision, attention, memory and decision-making.
The study involved 12 people with epilepsy who had fine wires implanted in their medial temporal lobe to detect seizures. This region of the brain is important for memory and the ability to recognize complex images, including faces.
While the brain recordings were transmitted to a computer, the research subjects viewed two pictures superimposed on a computer screen, each showing a familiar object, place, animal or person.
They were told to select one image as a target and to focus their thoughts on it until that image was fully visible and the other image faded away. The monitor was updated every one-tenth of one second based on the input from the brain recordings.
The subjects attempted this nearly 900 times in total, and were able to force the monitor to display the target image in 70 percent of these attempts. Subjects tended to learn the task very quickly, and often were successful on the first try.
Dr Fried's team first identified four brain cells with preferences for celebrities or familiar objects, animals or landmarks, and then targeted the recording electrodes to those cells.
They found that when subjects played the image-switching game, their success appeared to depend on their ability to power up cells that preferred the target image and suppress cells that preferred the non-target image.
"The remarkable aspects of this study are that we can concentrate our attention to make a choice by modulating so few brain cells and that we can learn to control those cells very quickly," said Debra Babcock, a program director at the National Institute of Neurological Disorders and Stroke.
"This is a novel and elegant use of a brain-computer interface to explore how the brain directs attention and makes choices."