Mapping phonemic processing zones along human perisylvian cortex: an electro-corticographic investigation

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Speech Processing

Background:

• The hierarchical organization of the auditory system processes complex features across cortical stages.
• The precise location and timing of phoneme processing in this hierarchy are debated.
• Previous non-invasive studies on phonemic representation yielded equivocal results, implicating different regions of the superior temporal gyrus (STG).

Purpose of the Study:

• To clarify the cortical regions involved in phoneme processing.
• To map phonemic representation across the left perisylvian cortex using high-density intracranial recordings.
• To investigate whether distinct divisions of the STG are sensitive to phonemic transitions.

Main Methods:

• Utilized intracranial recordings in humans for high signal-to-noise analysis at the individual participant level.
• Employed the mismatch negativity (MMN) as the primary electrophysiological measure.
• Presented oddball stimuli including phoneme pairs, spectro-temporally matched non-phonemes, and simple tones.

Main Results:

• The location of the mismatch negativity (MMN) response varied significantly with stimulus type.
• Phoneme representation was most prominent in the middle/anterior STG/STS.
• Phoneme representation was also detected in the posterior STG/SMG.

Conclusions:

• Phonemic processing occurs in multiple zones within the perisylvian cortex, extending beyond primary auditory areas.
• Both anterior and posterior regions of the STG contribute to phoneme representation.
• Findings support a dual-stream model of auditory processing, suggesting distinct ventral and dorsal pathways are engaged by speech stimuli.