Retinotopic and Orientation Tuning of Healthy Human Scalp EEG Alpha and Gamma Rhythms
Poster No:
1923
Submission Type:
Abstract Submission
Authors:
Sanaz Ghaffari Sarvarmaleki1, Russell Butler2
Institutions:
1Bishops university, Sherbrooke, QUEBEC, 2Bishop's University, Sherbrooke, Quebec
First Author:
Co-Author:
Introduction:
This study investigates the neural mechanisms underlying visual processing through the analysis of gamma and alpha brainwave responses. The methodology involved the selection of subjects based on their gamma response to a visual stimulus, followed by preprocessing and independent component analysis (ICA) to isolate relevant brainwave components. The study focused on examining the orientation tuning characteristics of gamma and alpha waves, discovering that gamma amplitude was significantly greater for oblique over cardinal orientations and exhibited specific preferences in terms of directionality. Notably, the gamma band showed strong retinotopic tuning, indicating a spatial correlation with visual field stimuli. The results also highlighted differences in orientation tuning between gamma and alpha responses, with gamma exhibiting a clearer preference and stronger retinotopic tuning than alpha. Furthermore, the study explored the spatial distribution of brainwave responses, revealing variations in gamma power across different visual field quadrants. The analysis was supported by data from 30 subjects, with 14 selected for in-depth analysis based on their gamma band response. This research contributes to our understanding of the spatial and orientation-specific processing of visual information in the brain, emphasizing the distinct roles of gamma and alpha waves in visual perception.
Methods:
1. Subjects were removed based on their gamma response to a full-field visual annulus. Subjects who did not respond to the grating were not considered for further analysis.
2. Preprocessing and ICA. Component selection was based on weight map and time-frequency gamma response. Components localized to the back of the head presenting narrow-band gamma responses were retained, all other components were discarded.
3. For peak frequency analysis, gamma and alpha were computed using separate window length. Peak frequency was calculated for each subject's alpha and gamma band separately. For scalp-space analysis a bandwidth was defined around each subject's alpha and gamma peak, and scalp-space power was filtered in those two separate bands to give alpha and gamma power at each electrode.
2. Preprocessing and ICA. Component selection was based on weight map and time-frequency gamma response. Components localized to the back of the head presenting narrow-band gamma responses were retained, all other components were discarded.
3. For peak frequency analysis, gamma and alpha were computed using separate window length. Peak frequency was calculated for each subject's alpha and gamma band separately. For scalp-space analysis a bandwidth was defined around each subject's alpha and gamma peak, and scalp-space power was filtered in those two separate bands to give alpha and gamma power at each electrode.
Results:
Orientation tuning: Gamma and alpha orientation tuning. Gamma orientation tuning (figure 1a) gamma amplitude was significantly greater (p=) at oblique over cardinal orientations. Gamma amplitude was larger for vertical over horizontal (p=) and also for left drifting vs right drifting orientations. The strongest gamma band response was for a left drifting grating at 45 degrees, the weakest for downward drifting horizontal grating (figure 1c) (full ERSP). Alpha orientation tuning was less consistent, the strongest alpha desynchronization was again for left drifting oblique, but there was no clear preference between oblique and cardinal (p=) or vertical vs horizontal. The most orientation sensitive frequency was the gamma peak and there was no significant difference in orientation selectivity across time points. There was no clear relationship between the alpha and gamma orientation tuning preferences (r=, p=). Peak frequency was not significantly different across orientations. Differences in spatial configuration of oblique vs cardinal.
·Orientations and directions
·All tuning
Conclusions:
This study reveals the functional organization of the human primary visual cortex using non-invasive EEG, focusing on retinotopic mapping and orientation tuning in alpha (8–15 Hz) and gamma (40–60 Hz) bands. Gamma rhythms showed strong orientation and spatial tuning, while alpha rhythms exhibited broader responses. Gamma activity was spatially specific and summated linearly across retinotopic regions, whereas alpha activity was widespread and less specific. These findings highlight distinct roles for alpha and gamma rhythms in visual processing, offering a non-invasive approach to study cortical organization in humans.
Modeling and Analysis Methods:
EEG/MEG Modeling and Analysis 2
Novel Imaging Acquisition Methods:
EEG 1
Keywords:
Attention Deficit Disorder
Cortex
Cortical Columns
Data analysis
Electroencephaolography (EEG)
ELECTROPHYSIOLOGY
Vision
1|2Indicates the priority used for review