The Zombie Within

A diagnostic cranial implant will typically contain 64 electrodes, each one a microthin wire that can potentially record the output of a single neuron. In practice, however, signals from neighboring neurons often blur together, and Reddy says she is lucky to get more than a couple of useful signals from each run. Moreover, patients awaiting brain surgery can’t be expected to endlessly look at pictures, so while most are very receptive to the research, time constraints are critical. Yet even under these conditions, Reddy and her predecessor Gabriel Kreiman have made some startling discoveries.

It turns out that in the medial temporal lobe many neurons respond only to specific categories of images. Fifteen percent seem to respond exclusively to faces or animals. It’s as if we are hard-wired to see them. That’s not surprising, Koch says, when you consider that “For most of human history, animals would have been either predators or lunch.” But how specific is our visual machinery? Kreiman, who is now at MIT, discovered that it can be highly specific. One neuron he recorded fired only when the patient was shown pictures of the Three Stooges’ Curly. In another patient, Kreiman found a neuron that responded only to images of Bill Clinton. “We don’t know how it would have reacted to Monica Lewinsky,” Reddy notes slyly.

At this early stage, it’s important not to make too grandiose claims, Reddy cautions, but the research bolsters Koch’s thesis that within the brain, consciousness is a local phenomenon. Kreiman showed that many neurons will respond only when we are consciously aware of the image we’re looking at. Reddy is now embarking on a series of experiments to determine if there are also neurons that fire when the patient isn’t aware. According to Koch’s new theory of mind, most of our brain is not involved in the state of conscious awareness. What Reddy is hoping to find is the empirical signature of this “zombie self.”

—M.W.