Brain sets sights on mind’s eye

Like a private movie screen showing personalized films, each person’s mind’s eye generates

a flow of imaginary visual scenes. These internal performances are inspired by a variety of

sources, from a riveting mystery novel to memories of last summer’s Olympics.

A new study by neuroscientists lends support to the notion that at least some of the brain

regions involved in visual perception of the external world animate the mind’s eye as well.

California researchers probed the neural roots of the mind’s eye in four men and five

women suffering from severe, uncontrollable brain seizures. So that the scientists could identify

the neural epicenter of the seizures for possible surgical removal, each patient had electrodes

implanted in the same general area of his or her brain for 1 to 2 weeks.

During that time, volunteers viewed pairs of pictures that included faces, objects, and

scenes. After looking at two images, they closed their eyes and imagined one of them, as specified

by the experimenters. As the trial proceeded for each participant, the implanted electrodes

recorded the rate of electrical bursts from nearly 300 individual nerve cells, or neurons.

Fourteen of these neurons exhibited matching rises and falls in electrical output when volunteers

viewed a picture and imagined the same picture. Some of these cells were in a visual-perception

area of the brain’s outer layer, or cortex, and others in inner structures linked to

memory and emotion. Gabriel Kreiman and Christof Koch of the California Institute of

Technology in Pasadena and Itzhak Fried of the University of California, Los Angeles School of

Medicine report their results in the Nov. 16 Nature.

They theorize that these brain cells belong to a neural system that orchestrates both the

storage of visual information and its recall during imagination. Earlier brain-scan studies of

healthy adults support this possibility (SN: 3/9/96, p. 155).

Another 28 neurons boosted their activity only when patients viewed pictures, and 7 neurons

responded only when patients imagined pictures. This fits with evidence that some forms

of brain damage impair the ability either to identify visually perceived objects or to form mental

images of them.