Shattered Nerves: How Science Is Solving Modern Medicine's Most Perplexing Problem

15 A Hole in the Center of the Brain

∑ 15 A Hole in the Center of the Brain The eventual answer to Alzheimer’s disease may be a chip in the brain. The same chip may also restore the lost capability to form and recover memories in those who have su√ered brain damage from stroke or disease. At least that will be the case if Theodore W. Berger, director of the Center for Neural Engineering and a professor of biomedical engineering and neuroscience at the University of Southern California, has his way. Berger has been aiming one way or another at the creation of such a cognitive chip since his graduate days at Harvard, where he earned a Ph.D. in neurobiology in 1976. Putting his goal in real-world vernacular, Berger said its purpose is to reverse ‘‘neurological conditions that result from some unfortunate event that produces a hole in the center of the brain.’’ The primary focus of his work is the hippocampus, which is many synapses removed from the sensory input and motor output portions of the brain where other neural prosthetic researchers are working. Shaped like a banana and the size of a thumb, the hippocampi—each of us has two of them—are located deep within each hemisphere. They are involved in the formation of new memories and in the conversion of short-term to longterm memories. Berger has chosen to work first in the hippocampus before tackling the restoration of functions performed by other parts of the brain, such as those responsible for the processing of language, because the hippo- A Hole in the Center of the Brain 245 campus is an evolutionarily primitive portion of the brain with a relatively simple cell structure. If one takes three slices of the hippocampus, the cells in each slice from top to bottom connect with each other. Other segments of the brain have a more complex cellular alignment structure, with cells connecting in a maze, much like a hodgepodge of wires plugged into an oldfashioned telephone switchboard. The memory implant that Berger is devising uses the hippocampus’s neat cellular alignment by acting as a bridge over damaged cells to reconnect the healthy cells on either side. It is Berger’s hypothesis that it is not necessary to know specifically what the damaged cells did in the memory-forming process in order to replace them. Nor is it necessary to understand what the action potentials, or pulse codes, that had been created by the damaged neurons mean in order to create a chip that replaces them. All one must do is provide a processing bridge to let the healthy cells on either side of the damaged area talk to each other through an implanted chip. The chip’s assigned task will be to do what neurons anywhere in the brain do, that is translate incoming pulse codes into di√erent outgoing pulse codes and then pass them on to neighboring neurons. Every time a neuron is activated by a pulse from a neighboring neuron, a variety of molecular changes begin to take place. The pulses fire o√ at anywhere from ten to thousands of times per second, and it is the di√erence in timing between the firings that essentially creates and carries information among neurons throughout the brain. The impact of an action potential on a receiving neuron generally lasts longer than the pulse itself. While the state of the neuron is changing in response to the first pulse it received, along comes another pulse from another nearby neuron, causing additional changes. This process continues until the neuron is altered to the point that it is ready to send o√ signals to its neighbors. This highly complex, and little understood, process going on virtually simultaneously in the billions of neurons that make up the brain gives us consciousness, memory, and the ability to contemplate our own being, which translates into mind. If a part of the brain—in this case the hippocampus—is damaged, the result is the hole in the brain to which Berger referred. The cells providing output to the now empty space have nowhere to send their signals, while the 246 Shattered Nerves cells on the other side of the gap receive nothing. Berger believes he can replace this hole with an implant by applying statistical analysis to the workings of the brain. He acknowledges, however, that developing a complete mathematical model of how the brain forms new...