IN PHILOSOPHY OF MIND, a “cerebroscope” is a fictitious device, a brain–computer interface in today’s language, which reads out the content of somebody’s brain. An autocerebroscope is a device applied to one’s own brain. You would be able to see your own brain in action, observing the fleeting bioelectric activity of all its nerve cells and thus of your own conscious mind. There is a strange loopiness about this idea. The mind observing its own brain gives rise to the very mind observing this brain. How will this weirdness affect the brain? Neuroscience has answered this question more quickly than many thought possible. But first, a bit of background.
Epileptic seizures—hypersynchronized, self-maintained neural discharges that can sometimes engulf the entire brain—are a common neurological disorder. These recurring and episodic brain spasms are kept in check with drugs that dampen excitation and boost inhibition in the underlying circuits. Medication does not always work, however. When a localized abnormality, such as scar tissue or developmental miswiring, is suspected of triggering the seizure, neurosurgeons may remove the offending tissue.
To minimize side effects, it is vital to pinpoint the location from which the seizures originate; neuropsychological testing, brain scans and EEGs aid this determination. But if no structural pathologies are apparent from the outside, doctors begin with an invasive procedure. The neurosurgeon inserts a dozen or so electrodes into the soft tissue of the brain, via small holes drilled through the skull, and leaves them in place for a week or so. During this time, the patient lives and sleeps in the hospital ward, and the signals from the wires are monitored continuously. When a seizure occurs, doctors triangulate the origin of the aberrant electrical activity. Subsequent destruction or removal of the offending chunk of tissue reduces the number of seizures—sometimes eliminating them entirely.
Neurosurgeon and neuroscientist Itzhak Fried of the David Geffen School of Medicine at U.C.L.A. is one of the world’s foremost specialists in this demanding trade, which requires great technical finesse. Fried and his colleagues perfected a variant of epilepsy monitoring in which the electrodes are hollowed out. This alteration permits them to insert tiny wires straight into the gray matter. Using appropriate electronics and fancy signal-detection algorithms, these miniaturized electrodes pick up the faint chattering of a bevy of just 10 to 50 neurons from the ceaseless background cacophony of the electrical activity of billions of cells.
From Senses to Memories
Under Fried’s supervision, a group from my laboratory—Rodrigo Quian Quiroga, Gabriel Kreiman and Leila Reddy—discovered a remarkable set of neurons in the jungles of the medial temporal lobe, the source of many epileptic seizures. This region, deep inside the brain, which includes the hippocampus, turns visual and other sensory percepts into memories.
We enlisted the help of several epileptic patients. While they waited for their seizures, we showed them about 100 pictures of familiar people, animals, landmark buildings and objects. We hoped one or more of the photographs would prompt some of the monitored neurons to fire a burst of action potentials. Most of the time the search turned up empty-handed, although sometimes we would come upon neurons that responded to categories of objects, such as animals, outdoor scenes or faces in general. But a few neurons were much more discerning. One hippocampal neuron responded only to photos of actress Jennifer Aniston but not to pictures of other blonde women or actresses; moreover, the cell fired in response to seven very different pictures of Jennifer Aniston. We found cells that responded to images of Mother Teresa, to cute little animals and to the Pythagorean theorem, a2 + b2 = c2.