Decoding inner language to treat speech disorders

Date:
January 12, 2022
Source:
Universite' de Gene`ve
Summary:
What if it were possible to decode the internal
language of individuals deprived of the ability to express
themselves? Researchers have now managed to identify promising
neural signals to capture our internal monologues. They were also
able to identify the brain areas to be observed to try to decipher
them in the future.



FULL STORY ==========================================================================
When human beings speak, different areas of their brain must be activated.

However, the function of these regions can be seriously impaired
after damage to the nervous system. For example, amyotrophic lateral
sclerosis (or Charcot's disease) can completely paralyze the muscles
used to speak. In other cases, following a stroke for example, areas
of the brain responsible for language can be affected: this is called
aphasia. However, in many of those cases, the ability of patients to
imagine words and sentences remains partly functional.


========================================================================== Decoding our internal speech is therefore of great interest to
neuroscience researchers. But the task is far from easy, as Timothe'e
Proix, scientist in the Department of Basic Neuroscience at the UNIGE
Faculty of Medicine, explains: "Several studies have been conducted
on the decoding of spoken language, but much less on the decoding of
imagined speech. This is because, in the latter case, the associated
neural signals are weak and variable compared to explicit speech. They
are therefore difficult to decode by learning algorithms." That is,
through computer programmes.

A well-hidden speech When a person speaks aloud, he or she produces
sounds that are emitted at certain precise moments. Researchers can
thus relate these tangible elements to the brain regions involved. In
the case of imagined speech, the process is much less easy. Scientists
have no obvious information on the sequencing and tempo of the words or sentences formulated internally by the individual. The areas recruited
in the brain are also less numerous and less active.

In order to perceive the neural signals of this very particular type of
speech, the UNIGE team used a panel of thirteen hospitalized patients,
in collaboration with two American hospitals. They collected data through electrodes implanted directly into patients' brains in order to assess
their epileptic disorders.

"We asked these people to say words and then to imagine them. Each
time, we reviewed several frequency bands of brain activity known to
be involved in language," explains Anne-Lise Giraud, a professor in
the Department of Basic Neuroscience at the UNIGE Faculty of Medicine,
and newly appointed director of the Institut de l'Audition in Paris.

Tapping into the right frequency The researchers observed several types
of frequencies produced by different brain areas when these patients
spoke, either orally or internally. "First of all, the oscillations
called theta (4-8Hz), which correspond to the average rhythm of syllable elocution. Then the gamma frequencies (25-35Hz), observed in the areas of
the brain where speech sounds are formed. Thirdly, beta waves (12- 18Hz) related to the cognitively more efficient regions solicited, for example
to anticipate and predict the evolution of a conversation. Finally,
the high frequencies (80-150Hz) that are observed when a person speaks
out" explains Pierre Me'gevand, assistant professor in the Department
of Clinical Neurosciences at the Faculty of Medicine of the UNIGE and
associate physician at the HUG.

Thanks to these observations, the scientists were able to show that the
low frequencies and the coupling between certain frequencies (beta and
gamma in particular) contain essential information for the decoding of
imagined speech.

Their research also reveals that the temporal cortex is an important
area for the eventual decoding of internal speech. Located in the left
lateral part of the brain, this specific cerebral region is involved
in the processing of information related to hearing and memory, but it
also houses a part of Wernicke's area, responsible for the perception
of words and language symbols.

These results are a major advance in the reconstruction of speech from
neural activity. "But we are still a long way from being able to decode imagined language," concludes the research team.

special promotion Explore the latest scientific research on sleep and
dreams in this free online course from New Scientist -- Sign_up_now_>>> academy.newscientist.com/courses/science-of-sleep-and-dreams ========================================================================== Story Source: Materials provided by Universite'_de_Gene`ve. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Timothe'e Proix, Jaime Delgado Saa, Andy Christen, Stephanie Martin,
Brian N. Pasley, Robert T. Knight, Xing Tian, David Poeppel,
Werner K.

Doyle, Orrin Devinsky, Luc H. Arnal, Pierre Me'gevand, Anne-Lise
Giraud.

Imagined speech can be decoded from low- and cross-frequency
intracranial EEG features. Nature Communications, 2022; 13 (1)
DOI: 10.1038/s41467- 021-27725-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220112093712.htm
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