Single-trial speech suppression of auditory cortex activity in humans

Area of Science:

• Neuroscience
• Auditory Neuroscience
• Speech Processing

Background:

• The human auditory cortex processes both external speech and self-vocalizations.
• Auditory cortex activity is typically suppressed during vocalization, attributed to motor cortex efference copy.
• Previous human studies using noninvasive methods showed only averaged suppression of auditory responses to self-speech.

Purpose of the Study:

• To investigate the discrepancy between primate single-unit and human noninvasive findings on auditory cortex responses to self-generated speech.
• To characterize the dynamic range of single-trial auditory responses in the human auditory cortex during vocalization.

Main Methods:

• Electrocorticography (ECoG) was used to record brain activity from neurosurgical subjects.
• Subjects performed auditory repetition tasks involving self-generated speech.
• High-gamma power (70-150 Hz) was analyzed to track single-trial auditory events.

Main Results:

• Auditory cortex suppression during vocalization varied across different cortical regions.
• Both suppressed and nonsuppressed auditory neuron responses to self-speech were observed.
• Single-trial high-gamma power reliably tracked auditory events and showed stable responses in both suppressed and nonsuppressed regions.

Conclusions:

• Human auditory cortex exhibits a diverse range of responses to self-generated speech, including both suppression and excitation.
• Electrocorticography reveals a richer dynamic of auditory processing during vocalization than previously shown by noninvasive methods.
• High-gamma activity provides a robust marker for tracking auditory events across trials, irrespective of suppression levels.