Discovery leads to schizophrenia questions

UC Irvine researchers have discovered that an unfamiliar link between auditory brain cells plays a vital role in sound cognition, a finding that could have widespread implications in the way scientists study sensory information processing in the brain.

Raju Metherate, the author of the study, published Sunday in Nature Neuroscience magazine, and fellow researchers Hideki Kawai and Ronit Lazar, found that the axon, the insulated hair-like fibers transmitting impulses from one cell to another, not only serves as a connection, but also as a regulator for information going through.

“This discovery was huge,” Metherate said. “This is a part of the brain that was thought did not do cognitive processes.”

The idea of the axon doing more than transporting information between brain cells is a novel one and could lead to more research on what role it may play in psychological disorders such as schizophrenia.

For those not familiar with neurobiology jargon, Metherate put it this way:

Imagine speaking into a landline telephone. When a person speaks into the handset, the sound waves are transferred into electrical energy, which flow through the phone cords to the handset the other person is listening to. When the electrical signal gets there, it is converted into the sound we hear coming through the earpiece.

Metherate’s team discovered that besides the volume controls on either party’s phone, the brain also has a volume control on the phone cord itself, or the axon.

“The result of our study suggests that we must consider the axons as sites of information processing — and of potential problems when things go wrong,” Metherate said.

Brain cells have dozens of dendrites and one axon which branches off, all sending and receiving information at the same time. What you get is one immensely complex network of electrical impulses and chemical reactions. Any kind of irregularity can be a symptom of a psychological disorder.

Schizophrenics, for example, sometimes have trouble hearing a person’s voice inflection, making it hard for them to tell if someone is happy or mad.

A part of that could be because schizophrenics generally have less “white matter” in the brain, Kawai suggested. White matter is a major axons crossroads in the brain. There are no brain cells there, only the white-colored, crisscrossing axons sending their information from the thalamus, where sensory information is received, to the cerebral cortex, where the information is interpreted.

Kawai points out that smoking has been known to regulate auditory function in schizophrenics, the nicotine making up chemical ground their brain cannot. Confirming nicotine’s role in auditory processing in 2004 led to this year’s discovery.

In 2004, Metherate’s team was using the brains of mice to confirm that the drug nicotine alters enhances cognition. Cognitive function occurs when millions of brain cells (there are about 100 billion of them) communicate with each other at the same time. This is the case in adult humans as well.

While the scientists were searching for answers in the cell body or in its receiving terminal called a dendrite, the nicotine was attaching itself to receptors along the early part of the axon — where information flows before it meets another cell’s dendrites.

“Nobody thought receptors would be there,” Kawai said. “That’s the biggest part of this discovery.”

When processing thought, a chemical called acetycholine latches onto the axon, among other things, enabling the information to run smoothly between brain cells. For schizophrenics the question becomes, are there not enough axon receptors, or simply not enough axons?

The team, in conjunction with fellow UCI neurobiologists, is already on the first task of answering that question — locating the receptors on the axon.

“We’re trying to find them as we speak,” Kawai said.

 UC Irvine scientists discovered cognitive processes on axons, fibers linking brain cells, opening the door for deeper exploration into sensory processing and psychological disorders such as schizophrenia.

 The discovery, three years in the making, confirms why researchers were previously unable to explain nicotine’s positive effects on cognition.

 Scientists will now move to locating the axon’s chemical receptors — the key to information processing — and seeing what role they may play in how schizophrenics process sound.

JOSEPH SERNA may be reached at (714) 966-4619 or at joseph.serna@latimes.com.