News Alerts  May 2, 2013--------News Archive

The experiments with rats imply that even though many neurons in the auditory cortex are "tuned" to low or high frequencies, most do not transmit their information directly to the striatum. Rather, their information is transmitted by a much smaller number of neurons in their vicinity, which convey their "votes" to the striatum.

How brain's auditory center transmits information for decisions and actions

Specialized neurons in the auditory cortex 'represent' and transmit the 'votes' of other neurons to the striatum

When a pedestrian hears the screech of a car's brakes, she has to decide if and how she should move in response. Is the action taking place blocks away, or 20 feet to the left? One of the truly primal mechanisms that we depend on every day of our lives — acting on the basis of our sense of hearing — is yielding its secrets to modern neuroscience.

A team of researchers from Cold Spring Harbor Laboratory (CSHL) has published their experimental results in the journal Nature, which they describe as surprising, even as they fill in a key piece of the puzzle of how mammals act on the basis of sound cues.

It's well known that sounds detected by the ears wind up in a part of the brain called the auditory cortex. There they are translated, or transduced, into information known as representations. Representations, in turn, become the basis upon which other parts of the brain make decisions and issue commands that generate specific muscle responses.

What scientists have not understood is what happens between the auditory cortex and portions of the brain that ultimately issue commands evoking a response to the sound of that car's screeching brakes. To find out, CSHL Professor Anthony Zador and Dr. Petr Znamenskiy trained rats to respond to sounds in a specific manner. When a high-frequency sound is played, the animals are rewarded if they move to the left. When the sound is low-pitched, the reward is given if the animal moves to the right.

To the striatum

On the simplest level, says Zador, "we know that sound is coming into the ear, and we know what's coming out in the end – a decision," in the form of a muscle movement. The surprise is the route the sound information used to perform the task in his experiments. "It turns out the information passes through a particular subset of neurons in the auditory cortex whose axons wind up in another part of the brain, called the striatum," said Zador.

A classic series of experiments provided inspiration for this work. Performed at Stanford University by William Newsome and colleagues, it involved the visual system of primates. Zador expected by analogy that representations formed in the auditory cortex would lead to end locations within the cortex.

Zador's experiments with rats imply that even though many neurons in the auditory cortex are "tuned" to low or high frequencies, most do not transmit their information directly to the striatum. Rather, their information is transmitted by a much smaller number of neurons in their vicinity, which convey their "votes" to the striatum.

Zador: "This is similar to the difference between a direct democracy and a representative democracy— the type we have in the United States. In a direct democracy model, every neuron activated by either a low or high pitched sound would have an equal 'vote.'  The information sent to the striatum for further action would be the equivalent of a simple sum of all these votes.

In reality, the neurons registering 'high' and 'low' are represented by a subset of neurons in their local area—which we might liken to members of Congress or the Electoral College—these in turn transmit the larger population votes to the auditory striatum where decisions are made and actions are taken."

"Corticostriatal neurones in auditory cortex drive decisions during auditory discrimination" appears online ahead of print in Nature on May 1, 2013. the authors are: Petr Znamenskiy and Anthony M. Zador. the paper can be obtained online at http://www.nature.com

About Cold Spring Harbor Laboratory
Founded in 1890, Cold Spring Harbor Laboratory (CSHL) has shaped contemporary biomedical research and education with programs in cancer, neuroscience, plant biology and quantitative biology. CSHL is ranked number one in the world by Thomson Reuters for impact of its research in molecular biology and genetics. The Laboratory has been home to eight Nobel Prize winners. Today, CSHL's multidisciplinary scientific community is more than 360 scientists strong and its Meetings & Courses program hosts more than 12,500 scientists from around the world each year to its Long Island campus and its China center. Tens of thousands more benefit from the research, reviews, and ideas published in journals and books distributed internationally by CSHL Press. The Laboratory's education arm also includes a graduate school and programs for undergraduates as well as middle and high school students and teachers. CSHL is a private, not-for-profit institution on the north shore of Long Island. For more information, visit http://www.cshl.edu.

Original article: http://www.uea.ac.uk/mac/comm/media/press/2013/May/rival-competition