Precise spatial tuning of visually driven alpha oscillations in human visual cortex

Area of Science:

• Neuroscience
• Visual Neuroscience
• Human Electrophysiology

Background:

• Alpha oscillations (8-12 Hz) in the occipital cortex are traditionally associated with cortical inactivity.
• Recent studies show conflicting evidence, suggesting alpha power may increase with visual stimulation.
• This discrepancy highlights a need to better understand the relationship between alpha oscillations and visual processing.

Purpose of the Study:

• To investigate the relationship between alpha oscillations and visual stimulation using intracranial recordings in humans.
• To differentiate between alpha oscillatory power and broadband power changes in response to visual stimuli.
• To model population receptive fields (pRFs) for both alpha and broadband power to understand their spatial properties.

Main Methods:

• Intracranial electroencephalography (iEEG) was used in human patients undergoing epilepsy monitoring.
• Visual stimuli were presented at varying locations across the visual field.
• A computational model was developed to separate alpha oscillatory power from broadband power.
• Population receptive field (pRF) models were fitted to both separated components.

Main Results:

• Alpha pRFs were found to be larger and have an inverse relationship with stimuli compared to broadband pRFs.
• Alpha oscillatory power decreased (suppressed) in response to visual stimuli within the receptive field.
• Broadband power increased in response to visual stimuli.
• The findings confirm alpha oscillations are linked to cortical inactivity, with suppression indicating activity.

Conclusions:

• Alpha power suppression in the human visual cortex is precisely tuned and indicates neural activity.
• Separating alpha oscillatory power from broadband power is essential for accurate analysis of visual responses.
• The characteristics of alpha pRFs, including their size and negative valence, help explain mechanisms of exogenous visual attention.