When we listen to speech sounds, the information coming into our left and right ears is not the same. This may be because acoustic information reaches one ear before the other, or because one of the ears sees the louder sound. Information about speech sounds also reaches different parts of our brain, and both hemispheres specialize in processing different types of acoustic information. But how does the brain absorb research information from different fields?
To investigate this question, lead researcher Basil Preisig from the University of Zurich collaborated with an international team of scientists. In an earlier study, the team found that the brain absorbs information about speech sounds by ‘balancing the rhythm of gamma waves across the hemispheres – a process known as’ oscillatory synchronization’. Preisig and his colleagues also found that they could affect the integration of speech sounds by altering the balancing process between the hemispheres. However, it was not yet clear where in the brain this process took place.
Did you hear ‘ga’ or ‘da’?
The researchers decided to apply electrical brain stimulation (routine high-density transcranial cellular stimulation or HD-TACS) to 28 healthy volunteers while their brains were scanned (by fMRI) at Center Donders for Cognitive Neuroimaging in Nijmegen. They created a syllable that was somewhere between ‘ga’ and ‘da’, and played this syllable to the participants’ right ear. At the same time, the mismatched information was played to the left ear. Participants were asked to indicate whether they heard ‘ga’ or ‘da’ at the push of a button. Would changing the connection between the two hemispheres also change the way the integrated information participants played to the left and right ear?
The scientists disturbed the ‘balance’ of gamma waves between the two hemispheres, which affected what the participants reported hearing (‘ga’ or ‘da’).
“This is the first demonstration in the field of research that intersex connections are important for the integration of speech-language information,” says Preisig. “This work paves the way for the study of other sensory processes and more complex auditory stimuli.” coordination, and how we can use experimental methods to handle this “adds senior author Alexis-Hervais Adelman.
The findings, to be published in PNAS, can also have clinical implications. “We know that disturbances of interrogative connection occur in phantom study ideas, such as tinnitus and verbal hallucinations,” Preisig explains. “Thus, by stimulating both hemispheres with (HD-) TACS can offer therapeutic benefits. I will continue this research by applying TACS in patients with hearing loss and tinnitus, to improve our understanding of cloud mind control and promote speech comprehension for this group. “
Max Planck Institute for Linguistics
Preisig, BC, et al. (2021) Selective alteration of interstitial connection with normal transcranial alternating stimulation affects binaural integration. PNAS. doi.org/10.1073/pnas.2015488118.