By Alison Abbott

People have used mind control to change images on a video screen, a study reports. The volunteers, whose brains were wired up to a computer, enhanced one of two competing images of famous people or objects by changing firing rates in individual brain cells.

[See a video on this finding here.]

The research, by Moran Cerf from the California Institute of Technology in Pasadena and his colleagues, demonstrates how our brains, which are constantly bombarded with images, noise and smells, can, through conscious thought, select what stimuli to notice and what to ignore.

The research is particularly exciting, says neuroengineer John Donoghue of Brown University, "because it shows how we can now peer into the process of thinking at a level we have not been able to get at before." Donoghue was responsible for the first successful transplantation of a chip into the motor cortex of a tetraplegic man, enabling him to move a computer cursor and manipulate a robotic arm with his mind.

The 12 patients involved in the study, published in the October 28 issue of Nature, suffered severe, treatment-resistant epilepsy, and were awaiting neurosurgery at the UCLA Ronald Reagan Medical Center in Los Angeles to remove the brain tissue responsible for initiating seizures. (Scientific American is part of Nature Publishing Group.) Neurosurgeon Itzhak Fried, an author on the new paper, wanted to identify the precise region responsible by implanting an array of 64 tiny electrodes into their brains around an area called the medial temporal lobe (MTL) and record from them constantly until a spontaneous seizure happened.

This area, which includes the hippocampus and is associated with memory, is a frequent source of epileptic seizures.

Neuroscientists have collaborated with Fried for many years, exploiting the waiting time of patients to do simple experiments to probe how the human mind works while listening in to the recording from the electrodes. Thanks to improved data analysis, they can now extract from noisy electrical background the firing of single neurons.

In the last six years or so they have shown that single neurons can fire when subjects recognize--or even imagine--just one particular person or object. They propose that activity in these neurons reflect the choices the brain is making about what sensory information it will consider further and what information it will neglect.

Mind reading

In this experiment, the scientists flashed a series of 110 familiar images--such as pictures of Marilyn Monroe or Michael Jackson--on a screen in front of each of the 12 patients and identified individual neurons which uniquely and reliably responded to one of the images. They selected four images for which they had found responsive neurons in different parts of a subject's MTL.

Then they showed the subject two images superimposed on each other. Each was 50 percent faded out.

The subjects were told to think about one of the images and enhance it. They were given ten seconds, during which time the scientists ran the firing of the relevant neurons through a decoder. They fed the decoded information back into the superimposed images, fading the image whose neuron was firing more slowly and enhancing the image whose neuron was firing more quickly.

Watching this on-line feedback, the subjects were able to make their targeted image completely visible, and entirely eliminate the distracting image, in more than two thirds of trials, and they learnt to do so very quickly.

Afterwards, they reported that they had used different cognitive strategies. Some tried to enhance the target image, while others tried to fade the distracting images. Both had worked. But feedback on the computer screens was vital. When this "brain-machine interface" wasn't provided, their success rates plummeted below one third.

The experiment shows how humans can use thinking to alter perception of competing visual images, says Cerf. "The environment offers some reality," he says, "but your own brain can shape it and override it with its internal deliberations."

In the future, he adds, this type of brain-machine interface may be exploited to read some thoughts of "locked-in" patients--who are awake but cannot communicate because they are paralyzed--by monitoring firing of neurons which respond to concepts such as "water" or "mother." That's science fiction at the moment though, he cautions.