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Sep. 6, 2013 -- "Should I say something or not?" Human beings are not alone in
pondering this dilemma -- animals also face decisions when they communicate by
voice. University of Tübingen neurobiologists Dr. Steffen Hage and Professor
Andreas Nieder have now demonstrated that nerve cells in the brain signal the
targeted initiation of calls -- forming the basis of voluntary vocal expression.
When we speak, we use the sounds we make for a specific purpose -- we
intentionally say what we think, or consciously withhold information. Animals,
however, usually make sounds according to what they feel at that moment. Even
our closest relations among the primates make sounds as a reflex based on their
mood. Now, Tübingen neuroscientists have shown that rhesus monkeys are able to
call (or be silent) on command. They can instrumentalize the sounds they make in
a targeted way, an important behavioral ability which we also use to put
language to a purpose.
To find out how the neural cells in the brain catalyse the production of
controled vocal noises, the researchers taught rhesus monkeys to call out
quickly when a spot appeared on a computer screen. While the monkeys solved
puzzles, measurements taken in their prefrontal cortex revealed astonishing
reactions in the cells there. The nerve cells became active whenever the monkey
saw the spot of light which was the instruction to call out. But if the monkey
simply called out spontaneously, these nerve cells were not activated. The cells
therefore did not signaled for just any vocalisation -- only for calls that the
monkey actively decided to make.
The results published in Nature Communications provide valuable insights into
the neurobiological foundations of vocalization. "We want to understand the
physiological mechanisms in the brain which lead to the voluntary production of
calls," says Dr. Steffen Hage of the Institute for Neurobiology, "because it
played a key role in the evolution of human ability to use speech." The study
offers important indicators of the function of part of the brain which in humans
has developed into one of the central locations for controlling speech.
"Disorders in this part of the human brain lead to severe speech disorders or
even complete loss of speech in the patient," Professor Andreas Nieder explains.
The results -- giving insights into how the production of sound is initiated --
may help us better understand speech disorders.