Scientists discover how brain's auditory center transmits information for decisions, actions

May 1, 2013, Cold Spring Harbor Laboratory

When a pedestrian hears the screech of a car's brakes, she has to decide whether, and if so, how, to 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 information gathered by our —is yielding its secrets to modern neuroscience. A team of researchers from Cold Spring Harbor Laboratory (CSHL) today publishes in the journal Nature which they describe as surprising. The results fill in a key piece of the puzzle about 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, where they are translated – transduced – into information that scientists call representations. These representations, in turn, form the informational basis upon which other can make decisions and issue commands for specific actions.

What scientists have not understood is what happens between the auditory cortex and portions of the brain that ultimately issue commands, say, for muscles to move in response to the sound of that car's screeching brakes. To find out, CSHL Professor Anthony Zador and Dr. Petr Znamenskiy trained rats to listen to sounds and to make decisions based on those sounds. 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 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 . The surprise, he says, is the destination of the information used by the animal to perform this task of discriminating between sounds of high and low frequency, as revealed in his team's 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 ," says Zador. The classic series of experiments that provided inspiration and a model for this work, performed at Stanford University by William Newsome and colleagues, involved the visual system of primates, and had led Zador to expect by analogy that representations formed in the auditory cortex would lead to other locations within the cortex.

These experiments in rats have implications for how neural circuits make decisions, according to Zador. Even though many neurons in 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" directly to the striatum.

"This is like the difference between a direct democracy and a representative democracy, of the type we have in the United States," Zador explains. "In a direct democracy model of how the auditory cortex conveys information to the rest of the brain, every neuron activated by a low- or high-pitched sound would have a 'vote.' Since there is noise in every perception, some minority of neurons will indicate 'low' when the sound is in fact 'high,' and vice-versa. In the direct democracy model, the information sent to the striatum for further action would be the equivalent of a simple sum of all these votes.

"In contrast – and this is what we found to be the case – the neurons registering 'high' and 'low' are represented by a specialized subset of neurons in their local area, which we might liken to members of Congress or the Electoral College: these in turn transmit the votes of the larger population to the place—in this case the auditory striatum—in which decisions are made and actions are taken."

"Corticostriatal neurones in drive decisions during auditory discrimination" appears online ahead of print in Nature on May 1, 2013.

Explore further: Rewired visual input to sound-processing part of the brain leads to compromised hearing

More information: Corticostriatal neurons in auditory cortex drive decisions during auditory discrimination, www.nature.com/nature/journal/ … ull/nature12077.html

Related Stories

Rewired visual input to sound-processing part of the brain leads to compromised hearing

August 22, 2012
Scientists at Georgia State University have found that the ability to hear is lessened when, as a result of injury, a region of the brain responsible for processing sounds receives both visual and auditory inputs.

Researchers pinpoint brain mechanisms that make the auditory system sensitive to behaviorally relevant sounds

April 2, 2013
(Medical Xpress)—How do we hear? More specifically, how does the auditory center of the brain discern important sounds – such as communication from members of the same species – from relatively irrelevant background ...

Interaction between auditory cortex and amygdala responsible for our response to unpleasant sounds, research finds

October 10, 2012
(Medical Xpress)—Heightened activity between the emotional and auditory parts of the brain explains why the sound of chalk on a blackboard or a knife on a bottle is so unpleasant.

Recommended for you

Research reveals atomic-level changes in ALS-linked protein

January 18, 2018
For the first time, researchers have described atom-by-atom changes in a family of proteins linked to amyotrophic lateral sclerosis (ALS), a group of brain disorders known as frontotemporal dementia and degenerative diseases ...

Fragile X finding shows normal neurons that interact poorly

January 18, 2018
Neurons in mice afflicted with the genetic defect that causes Fragile X syndrome (FXS) appear similar to those in healthy mice, but these neurons fail to interact normally, resulting in the long-known cognitive impairments, ...

How your brain remembers what you had for dinner last night

January 17, 2018
Confirming earlier computational models, researchers at University of California San Diego and UC San Diego School of Medicine, with colleagues in Arizona and Louisiana, report that episodic memories are encoded in the hippocampus ...

Recording a thought's fleeting trip through the brain

January 17, 2018
University of California, Berkeley neuroscientists have tracked the progress of a thought through the brain, showing clearly how the prefrontal cortex at the front of the brain coordinates activity to help us act in response ...

Midbrain 'start neurons' control whether we walk or run

January 17, 2018
Locomotion comprises the most fundamental movements we perform. It is a complex sequence from initiating the first step, to stopping when we reach our goal. At the same time, locomotion is executed at different speeds to ...

Miles Davis is not Mozart: The brains of jazz and classical pianists work differently

January 16, 2018
Keith Jarret, world-famous jazz pianist, once answered in an interview when asked if he would ever be interested in doing a concert where he would play both jazz and classical music: "No, that's hilarious. [...] It's like ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.