Their findings could eventually lead to new ways to control a computer using the mind alone, although the researchers do not see any immediate applications. More interesting to them is what their experiment reveals about how the brain works.
The brain can “choose” to notice one image over another by stepping up the activity of one brain cell and stopping the activity of another, the team at the California Institute of Technology reported in the journal Nature.
The Caltech researchers took advantage of a completely unrelated medical trial for treating severe epilepsy. They recruited patients whose brain tremors could not be treated well by drugs, who had signed up for surgery.
The dysfunction for these particular patients was in a part of the brain called the medial temporal lobe, which is involved in the higher processing of information. “The medial temporal lobe is pretty much in the centre of the brain,” Moran Cerf, who led the research, said in a telephone interview.
This part of the brain has a backup, Cerf said. “You can take part of the brain out but the patient doesn’t lose any function,” he said. The patients had volunteered for this procedure, but in order to take out the right part, the doctors had to see an epileptic seizure in real time. So each patient had electrodes implanted in the brain and then waited for a seizure.
Cerf and colleagues recruited them for their own experiment in the meantime.
Caltech’s Itzhak Fried, who oversaw the research, led a team that found out in 2005 that people have a “Halle Berry neuron”—a brain cell responsible for recognising a particular movie star.
The epilepsy patients were tested to see just what stimulus would activate the particular neurons they had hooked up to the electrodes. One patient, for instance, liked singer Johnny Cash and one of her electrodes activated strongly when she viewed pictures of the country music star.
They designed a computer that could recognise these signals and control a programme to fade pictures in and out on a screen. “It is kind of like a thought projector, we call it,” Cerf said.
The researchers super-imposed two images — say singer-musician Johnny Cash superimposed over the actress Marilyn Monroe. The 12 volunteers were asked to fade one image up and the other down, using only their thoughts.
They were able to do so 69 per cent of the time, as the computer recognised the firing of the “Johnny Cash” neuron or the “Marilyn Monroe” neuron, Cerf said.
It was a highly individualised process, based on each patient's preferences.
Cerf is unsure about real-world applications of the technology, because the neurons involved are fickle, he says.
“They change their properties often. On day one they might fire for Marilyn Monroe, on day two they fire for something else,” he said. “They are not the best neurons for a brain-machine interface.”
Researchers trying to make mind-controlled machines have helped a boy with epilepsy play computer games using a brain implant, and have used electroencephalography or EEG signals to help patients control computer cursors.