Scientists reaching consensus on how brain processes speech

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Scientists reaching consensus on how brain processes speech

May 26, 2009

Source: town University Medical Center

Neuroscientists feel they are much closer to an accepted unified theory about

how the brain processes speech and language, according to a scientist at

town University Medical Center who first laid the concepts a decade ago

and who has now published a review article confirming the theory.

In the June issue of Nature Neuroscience, the investigator, f Rauschecker,

PhD, and his co-author, Sophie , PhD, a neuroscientist at University

College, London, say that both human and non-human primate studies have

confirmed that speech, one important facet of language, is processed in the

brain along two parallel pathways, each of which run from lower- to

higher-functioning neural regions.

These pathways are dubbed the " what " and " where " streams and are roughly

analogous to how the brain processes sight, but are located in different

regions, says Rauschecker, a professor in the department of physiology and

biophysics and a member of the town Institute for Cognitive and

Computational Sciences.

Both pathways begin with the processing of signals in the auditory cortex,

located inside a deep fissure on the side of the brain underneath the temples -

the so-called " temporal lobe. " Information processed by the " what " pathway then

flows forward along the outside of the temporal lobe, and the job of that

pathway is to recognize complex auditory signals, which include communication

sounds and their meaning (semantics). The " where " pathway is mostly in the

parietal lobe, above the temporal lobe, and it processes spatial aspects of a

sound - its location and its motion in space - but is also involved in providing

feedback during the act of speaking.

Auditory perception - the processing and interpretation of sound information -

is tied to anatomical structures; signals move from lower to higher brain

regions, Rauschecker says. " Sound as a whole enters the ear canal and is first

broken down into single tone frequencies, then higher-up neurons respond only to

more complex sounds, including those used in the recognition of speech, as the

neural representation of the sound moves through the various brain regions, " he

says.

Both human and nonhuman primate studies were examined in this review.

In humans, researchers use functional magnetic resonance imaging (fMRI) to

" watch " activity move between brain regions in experiments testing speech

" (re)cognition, " Rauschecker says. In non-human primates, investigators use a

technique known as single-cell recording, which can measure changes within a

single neuron. To do this, anesthetized animals are equipped with

microelectrodes that can pick up activity in pinpointed brain areas, a technique

that can be used only rarely in human patients but provides much better

resolution.

" In both species, we are using species-specific communication sounds for

stimulation, such as speech in humans and rhesus-specific calls in rhesus

monkeys, " Rauschecker says. " We find that the structure of these communication

sounds is similar across species. "

What is so interesting to Rauschecker is that although speech and language are

considered to be uniquely human abilities, the emerging picture of brain

processing of language suggests " in evolution, language must have emerged from

neural mechanisms at least partially available in animals, " he says.

" Speech, or the early process of language, is well modeled by animal

communication systems, and these studies now demonstrate that primate auditory

cortex, across species, displays the same patterns of hierarchical structure,

topographic mapping, and streams of functional processing, " Rauschecker says.

" There appears to be a conservation of certain processing pathways through

evolution in humans and nonhuman primates. "

While this research is basic science trying to solve fundamental questions about

the brain, it may ultimately yield some valuable insights into disorders that

involve problems in comprehending auditory signals, such as autism and

schizophrenia, he says.

" Understanding speech is one of the major problems seen in autism, and a person

with schizophrenia hears sounds that are just hallucinations, " Rauschecker says.

" Eventually, this area of research will lead us to better treatment for these

issues.

" But mostly, we are fascinated by the fact that humans can make such exquisite

sense of the slight variation in sound waves that reach our ears, and only

lately have we been able to model how the brain knows how to attach meaning to

these sounds in terms of communication. " he says.

 

Love, Gabby. :0)

http://stemcellforautism.blogspot.com/

 

" I know of nobody who is purely Autistic or purely neurotypical. Even God had

some Autistic moments, which is why the planets all spin. " ~ Jerry Newport