Single nerve cells react to different vowel sounds, Israeli scientists discover
The researchers found that certain nerve cells responded with increased activity to vocalizations of certain vowels, while ignoring others.
Israeli scientists have discovered that individual nerve cells react to the vocalization of specific vowels. In the study, recently published in the online journal Nature Communications, certain nerve cells responded with increased activity to certain vowels and "ignored" others.
The study was led by Prof. Shy Shoham and Dr. Ariel Tankus of the biomedical engineering department at the Technion - Israel Institute of Technology, Haifa, in cooperation with Itzhak Fried, professor of neurosurgery at the University of California, Los Angeles, and the Tel Aviv Sourasky Medical Center.
The researchers wanted to map the electrical activity of the brain when a subject articulates different vowels, and they turned to volunteers with epilepsy who already had electrodes placed in their brains as part of their treatment.
The electrodes were located in two areas of the brain connected to speech, and in these areas the researchers examined a group of hundreds of nerve cells. As they mapped the brain activity, the scientists discovered certain nerve cells that reacted only when specific vowels were articulated.
"We discovered that when you say 'i', for example, a specific nerve cell reacts, and when you say 'a,' another cell reacts," Shoham said. The cells' selectiveness was outstanding, he added, explaining that one cell reacted only to 'ah,' but not consistently. "It was very strange so we returned to the recording, and it turned out that those times the cell didn't react, the vowel was actually 'aaaah.' It's possible that the selectiveness is at that level, too."
The new findings support two central, and often contradictory, approaches to brain research. "There are currently two parallel paradigms in brain research, and each has its supporting evidence," Shoham said. "The amazing thing about this research is that we found examples of both leading paradigms. One paradigm claims that cells are very selective and react to very specific things. Fried discovered what can be called 'concept' cells, such as 'Jennifer Aniston cells.' These cells reacted to [American actress] Jennifer Aniston, whether it was her photo or her name. The selective paradigm has been the central paradigm in brain research for the past 50 years or more," Shoham added.
According to the second paradigm, he continued, "different nerve cells react in a graded manner to many different things." A concept or certain image can elicit a different response than another concept or image, but both concepts or images influence some of the same nerve cells. The researchers discovered examples of the first approach in one area of the brain, and examples of the second approach in another area.
The scientists noticed another interesting phenomenon. Language scholars map relations between different vowels according to the similarity in their articulation, as presented in the International Phonetic Alphabet vowel chart. The researchers discovered a correlation between the chart and patterns of brain activity.
Shoham believes the research has practical applications, which were the primary motivation for the research. Mapping brain activity while a subject articulates certain syllables enables a computer program to learn and recreate the exact articulation by identifying the brain activity.
Shoham believes this process has the potential to enable paralyzed people to develop speech capabilities. "Instead of teaching the computer program to identify brain activity related to 200 words, the system identifies one syllable after the other. The second part of such a system could translate this flow of syllables into words."