Spoken language coding neurons in the Visual Word Form Area: Evidence from a TMS adaptation paradigm

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• The left ventral occipito-temporal cortex (left-vOT), or Visual Word Form Area, is crucial for reading.
• This area also responds to speech, leading to debate about how it processes different language forms.

Purpose of the Study:

• To investigate whether the left-vOT contains modality-specific neurons, multimodal neurons, or top-down processing for speech.
• To differentiate between competing hypotheses explaining cross-modal activation in the left-vOT.

Main Methods:

• Utilized a transcranial magnetic stimulation (TMS)-adaptation protocol.
• Adapted left-vOT neurons using either spoken or written words.
• Assessed lexical decisions on spoken and written targets after adaptation, with TMS applied to the left-vOT.

Main Results:

• TMS adaptation selectively facilitated lexical decisions when the initial adaptation modality matched the target stimulus modality.
• Within-modal adaptation effects were observed for both spoken and written words.
• No evidence of cross-modal adaptation was found, indicating modality-specific processing.

Conclusions:

• Findings suggest the left-vOT contains functionally segregated neuronal populations for spoken and written language.
• This challenges hypotheses of purely visual word form neurons or multimodal neurons in this area.
• Supports a model where distinct neural populations within the left-vOT encode different language modalities.