Modality-Specific and Amodal Language Processing by Single Neurons

Area of Science:

• Neuroscience
• Psycholinguistics
• Computational Linguistics

Background:

• Psycholinguistic theories propose separate processing for spoken (phonological) and written (orthographic) language, converging into unified semantic and syntactic codes.
• Previous brain imaging studies identified regions but lacked the resolution to pinpoint specific neural codes for language processing stages.

Purpose of the Study:

• To investigate the neural codes underlying spoken and written language comprehension at the single-neuron and mesoscale levels.
• To determine which sensory and abstract linguistic dimensions are encoded by neural activity in different brain regions.

Main Methods:

• Recorded neuronal firing and mesoscale field potentials from over 1000 neurons and 1400+ microwires/iEEG contacts in 21 awake neurosurgical patients.
• Utilized forward modeling of temporal receptive fields to analyze neural responses during written and spoken sentence comprehension.

Main Results:

• Discovered a double dissociation: superior temporal neurons responded to phonemes/phonological features, while ventral occipito-temporal neurons responded to letters/orthographic features.
• Identified novel, modality-independent neurons in middle temporal and inferior frontal areas responsive to higher-level linguistic features.

Conclusions:

• Language processing involves distinct neural dynamics across multiple brain regions, from sensory features to abstract linguistic information.
• Findings link neural activity at various resolutions, down to the single-neuron level, to specific stages of language comprehension.