Language and Humor Blog

A recent study using positron emission tomography (PET) with macaques/rhesus monkeys shows evidence that they process their species’ oral signals differently from other sounds (as humans do with language) and in brain regions analogous to those used by humans for processing language.

In sum:

Although the coo of a monkey is acoustically very different from a high-pitched [monkey] scream, the researchers found that both of these meaningful species-specific sounds elicited significantly more activity than the non-biological control stimuli in the same three regions of the macaque’s brain. Moreover, these regions correspond to the key language centers in humans, with the ventral premotor cortex (PMv) corresponding to Broca’s area, and the temporoparietal area (Tpt) and posterior parietal cortex (PPC) corresponding to Wernicke’s area. In contrast, the non-biological sounds — which were acoustically similar to the coos and screams but had no meaning for the animals — elicited significantly less activity in these regions; rather, they were associated with greater activation of the brain’s primary auditory areas.

[Here's the full press release from America's National Institute on Deafness and Other Communication Disorders and its National Institute of Mental Health about their joint research published in Nature Neuroscience.]

Another recent study focuses on how and when human babies start to connect listening to language with producing it.

This quote is similar to the macaque-study quote above:

“The brain is going into its environment and selectively grabbing out sounds that have to do with speech and processing them in a completely different way from the way that other sounds are being processed,” says Bill Greenough, a neuroscientist with the University of Illinois at Urbana-Champaign.

However, this is not new. What is new about this study is the methodology of using magnetoencephalography (MEG) to measure the millisecond-by-millisecond electrical activity of newborn, six-month-old and one-year-old babies’ brains to see when both the chiefly listening-related and the chiefly speaking-related parts of the brain get activated.

This press release gives more information about the baby research (by the University of Washington’s Institute for Brain and Learning Sciences, published in NeuroReport.

Conclusion:

At all three ages the infants showed activation in the temporal part of the brain, Broca’s [sic] area, that is responsible for listening and understanding speech, showing they were able to detect sound changes for all three stimuli. But the pure perception of sound did not activate the areas of the brain responsible for speaking. However, researchers began seeing some activation in Broca’s area when the 6-month-old infants heard the syllables or harmonic chords. By the time the infants were one-year old, the speech stimuli activated Broca’s area simultaneously with the auditory areas, indicating “cross-talk” between the area of the brain that hears language and the area that produces language, according to [neuroscientist Patricia] Kuhl.

Unfortunately, there’s an error in there. The press release should say: “the infants showed activation in the temporal part of the brain, Wernicke’s area, that is responsible for listening and understanding speech.” The second mention of Broca’s area implies correctly that Broca’s area is the main area involved in speaking (and the article earlier says this explicitly) not listening. Broca’s area is also in the frontal lobe not the temporal lobe, where Wernicke’s area is located.

I’m curious what a larger study of babies, with a greater number of test subjects and a greater range of ages (and nationalities beyond just Finnish), would show. At or soon after twelve months of age, a lot of babies are speaking some single words with the purpose of communicating whole ideas (holophrastic speech), so I think the brain connection between reception and production is probably (typically) earlier than twelve months. Having newborn, six months, and twelve months for subject ages is understandable for an early study, but at that period there are huge developmental leaps. Let’s await further research.